JP2006088518A - Heat-shrinkable polylactic acid film - Google Patents

Abstract

An object of the present invention is to improve the fracture resistance of a fusing seal part without causing environmental problems, and to reduce the hardness of square portions generated at the four corners of a bag after shrinkage.
The composition ratio of biodegradable aromatic aliphatic polyester and D-lactic acid and L-lactic acid is 98.0: 2.0 to 85.0: 15.0 or 2.0: 98.0. It consists of a resin mixture with a polylactic acid polymer of ˜15.0: 85.0, and 50 to 90 mol% of the dicarboxylic acid component constituting the biodegradable aromatic aliphatic polyester is an aliphatic dicarboxylic acid. The layer in which the content of the biodegradable aromatic aliphatic polyester is 70 to 90% by weight of the resin mixture is a central layer, and the constituent ratio of D-lactic acid and L-lactic acid is 95.0: 5. A heat-shrinkable polylactic acid film having a polylactic acid polymer of 0 to 88.0: 12.0 or 5.0: 95.0 to 12.0: 88.0 as an outermost layer is used.
[Selection figure] None

Description

  The present invention relates to a heat-shrinkable polylactic acid film.

  Conventionally, in the packaging industry, heat-shrinkable films that shrink in the biaxial direction are used for packaging products, for example, for packaging cosmetic containers such as oval bottles, round bottles, and tubes, and for containers such as natto and pudding. About 2 to 4 pieces are used for collective packaging arranged on a paper mount and for collective packaging of dry batteries.

  As materials used for these heat-shrinkable films, polypropylene, electron-irradiated polyethylene, polyvinyl chloride (PVC), and the like are known, and are widely used and consumed in industry.

  However, these films have excellent properties as heat-shrinkable films, but when discarded in the natural environment after use, they remain undecomposed due to their stability and damage the landscape. It causes problems such as polluting the living environment such as fish and wild birds.

  On the other hand, various materials made of degradable resins that do not cause environmental problems have been studied. One of them is polylactic acid. It is known that polylactic acid is naturally hydrolyzed in the soil so that the original form does not remain in the soil and becomes a harmless decomposition product by microorganisms.

  However, the polylactic acid may have a problem in workability due to the inherent rigidity of the material.

  As an improvement method thereof, a method of blending polylactic acid with a soft biodegradable resin is known. For example, Patent Document 1 discloses blending an aliphatic polyester with polylactic acid, Patent Document 2 discloses blending polycaprolactone with polylactic acid, and Patent Document 3 discloses polylactic acid / polylactic acid. It has been disclosed to adjust the composition ratio of L-lactic acid and D-lactic acid of polylactic acid in a blend system of aliphatic polyester.

  Patent Document 4 discloses that a layer made of polylactic acid is laminated outside a layer made of a polylactic acid / aliphatic polyester blend system in order to ensure transparency. A laminated film of resins having different mechanical properties is disclosed.

JP-A-9-169896 JP-A-8-300481 JP 2001-11214 A JP 2001-47583 A JP 2003-72010 A

  However, in any of the above cases, when packaging a product as a heat-shrinkable film, it breaks from the melt-sealed seal portion, or the square portions that occur at the four corners of the bag after shrinkage become hard, causing damage to the human body. May be attached.

  Therefore, the present invention aims to improve the fracture resistance of the fusing seal part without causing environmental problems, and to reduce the hardness of the square portions generated at the four corners of the bag after shrinkage. .

  In the present invention, the constituent ratio of the biodegradable aromatic aliphatic polyester and D-lactic acid and L-lactic acid is 98.0: 2.0 to 85.0: 15.0 or 2.0: 98.0. It consists of a resin mixture with a polylactic acid polymer of ˜15.0: 85.0, and 50 to 90 mol% of the dicarboxylic acid component constituting the biodegradable aromatic aliphatic polyester is an aliphatic dicarboxylic acid. The layer in which the content of the biodegradable aromatic aliphatic polyester is 70 to 90% by weight of the resin mixture is a central layer, and the constituent ratio of D-lactic acid and L-lactic acid is 95.0: 5. By using a heat-shrinkable polylactic acid-based film having a polylactic acid-based polymer of 0-88.0: 12.0 or 5.0: 95.0-12.0: 88.0 as the outermost layer. The above problem has been solved.

  Since the heat-shrinkable polylactic acid-based film according to the present invention has a specific center layer having a polylactic acid-based polymer and a specific outermost layer having a polylactic acid-based polymer, without causing environmental problems, The fracturing resistance of the fusing seal can be improved, and the hardness of the square portions generated at the four corners of the bag after shrinkage can be reduced.

  The heat-shrinkable polylactic acid film according to the present invention has a layer composed of a predetermined polylactic acid polymer and a predetermined biodegradable aromatic aliphatic polyester as a central layer, and the predetermined polylactic acid polymer is the most preferred. It is a laminated film having an outer layer and these center layer and outermost layer.

First, the center layer will be described.
The polylactic acid-based polymer constituting the central layer is a polymer of lactic acid, specifically, a homopolymer having a structural unit of L-lactic acid or D-lactic acid, that is, poly (L-lactic acid) or poly ( D-lactic acid) or a copolymer having a structural unit having both L-lactic acid and D-lactic acid, that is, poly (DL-lactic acid) or a mixture thereof.

  As a polymerization method for the polylactic acid polymer, known methods such as a condensation polymerization method and 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.

  Further, in the ring-opening polymerization method (lactide method), lactide which is a cyclic dimer of lactic acid is subjected to ring-opening polymerization in the presence of a predetermined catalyst while using a polymerization regulator or the like as required. A polylactic acid polymer having a composition can be obtained.

  The lactide includes L-lactide, which is a dimer of L-lactic acid, D-lactide, which is a dimer of D-lactic acid, and DL-lactide, which is a dimer of D-lactic acid and L-lactic acid. These may be mixed and polymerized as necessary to obtain polylactic acid having an arbitrary composition and crystallinity.

  A polylactic acid polymer in which the constituent ratio of D-lactic acid and L-lactic acid is 100: 0 or 0: 100 becomes a very high crystalline resin, has a high melting point, and tends to have excellent heat resistance and mechanical properties. Become. However, when used as a heat-shrinkable film, if the crystallinity becomes very high, stretch orientation crystallization proceeds at the time of stretching, and it is difficult to adjust the heat shrinkage rate. Even when a film in an amorphous state is obtained under stretching conditions, crystallization proceeds due to heat during shrinkage, and shrinkage finish tends to decrease. On the other hand, in the case of a polylactic acid polymer having both D-lactic acid and L-lactic acid as constituent components, the crystallinity may decrease as the content ratio of the optical isomer with a small content increases. Are known.

  For this reason, when using as a heat-shrinkable film, it is preferable to adjust the mixing ratio of D-lactic acid and L-lactic acid used at the time of superposition | polymerization. Moreover, the mixing ratio of D-lactic acid and L-lactic acid can be adjusted by mixing two or more types of polylactic acid polymers having different mixing ratios of D-lactic acid and L-lactic acid.

  In this invention, the composition ratio of D-lactic acid and L-lactic acid in the polylactic acid polymer used in the resin constituting the intermediate layer is 98.0: 2.0 to 85.0: 15.0, Or 2.0: 98.0 to 15.0: 85.0, 97.0: 3.0 to 87.0: 13.0, or 3.0: 97.0 to 13.0: 87.0 is preferred. By making the constituent ratio of D-lactic acid and L-lactic acid within the above range, it becomes possible to appropriately adjust the orientation crystallization at the time of stretching, and the crystallization at the time of shrinkage is also reduced, which is favorable. It becomes possible to obtain shrink finish.

  The preferred range of the weight average molecular weight of the polylactic acid polymer is 50,000 to 400,000, more preferably 100,000 to 250,000. If the weight average molecular weight is too small, it tends to break. On the other hand, if the weight average molecular weight is too large, molding tends to be difficult.

  Examples of the polylactic acid-based polymer include: Lacty series manufactured by Shimadzu Corporation, Lacia series manufactured by Mitsui Chemicals, and Nature Works series manufactured by Cargill Dow.

  Next, the biodegradable aromatic aliphatic polyester constituting the central layer is a polyester obtained from a dicarboxylic acid component composed of an aromatic dicarboxylic acid component and an aliphatic dicarboxylic acid component, and an aliphatic diol component. .

  Examples of the aromatic dicarboxylic acid include isophthalic acid, terephthalic acid, and 2,6-naphthalenedicarboxylic acid. Examples of the aliphatic dicarboxylic acid include succinic acid, adipic acid, suberic acid, sebacic acid, and dodecanedioic acid. Examples include acids. Furthermore, examples of the aliphatic diol include ethylene glycol, 1,4-butanediol, 1,4-cyclohexanedimethanol and the like. Each of these aromatic dicarboxylic acid component, aliphatic dicarboxylic acid component, and aliphatic diol component may be used alone or in combination of two or more compounds. Among these, it is more preferable to use terephthalic acid as the aromatic dicarboxylic acid component, adipic acid as the aliphatic dicarboxylic acid component, and 1,4-butanediol as the aliphatic diol component.

  The content of the aliphatic dicarboxylic acid in the dicarboxylic acid component constituting the biodegradable aromatic aliphatic polyester needs to be 50 to 90 mol%, and preferably 50 to 70 mol%. If it is less than 50 mol%, it may be difficult to develop the biodegradability of the resulting biodegradable aromatic aliphatic polyester. On the other hand, when it is more than 90 mol%, the crystal acceleration becomes faster and the stretchability tends to decrease.

  Examples of such biodegradable aromatic aliphatic polyesters include copolymers of polybutylene adipate and terephthalate (BASF: Ecoflex), tetramethylene adipate, And a copolymer with terephthalate (Easman Chemicals: Easter Bio).

  The content of the biodegradable aromatic aliphatic polyester with respect to the resin mixture of the polylactic acid polymer constituting the biodegradable aromatic aliphatic polyester according to the present invention and the biodegradable aromatic aliphatic polyester is, 70 to 90% by weight is preferable, and 75 to 85% by weight is preferable. If it is less than 70% by weight, it may be insufficient to lower the rigidity of the resulting film. On the other hand, if it is more than 90% by weight, the natural shrinkage, that is, the shrinkage of the film that occurs during the period of standing at room temperature tends to increase.

Next, the outermost layer will be described.
The polylactic acid polymer constituting the outermost layer may be the same as the polylactic acid polymer constituting the central layer. However, the constituent ratio of D-lactic acid and L-lactic acid is preferably 95.0: 5.0 to 88.0: 12.0, or 5.0: 95.0 to 12.0: 88.0. 94.0: 6.0-90.0: 10.0 or 6.0: 94.0-10.0: 90.0.

  The polylactic acid polymer and the aliphatic aromatic polyester constituting the central layer have different deformation behaviors when stretched. Therefore, when the mixture of both resins is stretched, the surface becomes rough and the haze is greatly reduced. Tend to. This tendency increases as components other than the polylactic acid-based polymer increase and diffusion of transmitted light occurs, resulting in an increase in haze and a decrease in transparency. By suppressing this surface roughness, transparency can be maintained, but as this method, a layer having the above-mentioned proportion of D-lactic acid and L-lactic acid is provided in the outermost layer.

  When the amount of D-lactic acid or L-lactic acid in the polylactic acid polymer constituting the polylactic acid polymer constituting the outermost layer is less than 5.0%, the crystallinity becomes high, and during heat shrinkage It causes a defect. That is, since crystallization proceeds simultaneously at the time of heat shrinkage, if a hot air shrinker having a large temperature unevenness is used, the shrinkage rate becomes uneven at the film position, and the finish quality is lowered. On the other hand, when steam shrinker is used, the deterioration of finish due to uneven shrinkage is not particularly noticeable, but the film is whitened due to the effect of crystallization, which is not preferable for the recent film with an emphasis on appearance.

  On the other hand, if the amount of D-lactic acid or L-lactic acid in the polylactic acid polymer constituting the polylactic acid polymer constituting the outermost layer is more than 12.0%, the crystallinity is almost lost. If the products collide with each other immediately after heat shrinkage, the film is likely to be fused and a hole is easily opened.

  By the way, by using the above-mentioned polylactic acid polymer for the outermost layer, it becomes possible to improve the slipperiness of the obtained film. Further, inorganic particles may be added as a method for improving slipperiness. Examples of the inorganic particles include inorganic particles such as silica, talc and kaolin.

  The average particle size of the inorganic particles is preferably 0.5 to 5 μm. Moreover, 0.01-5 weight part is preferable with respect to 100 weight part of resin which comprises outermost layer, and, as for the addition amount, 0.05-3 weight part is more preferable.

  Since the surface of the inorganic particles is roughened by moving to the surface during stretching, slipperiness is imparted to the film. However, although the degree of transition to the surface depends on the stretching conditions, the maximum effect can be found with the minimum addition amount by adjusting the crystallinity of the outermost layer as in the present invention. .

  The content of the polylactic acid polymer in the outermost layer is preferably 90% by weight or more, more preferably 95% by weight or more, and particularly preferably 100% by weight. If it is less than 90% by weight, surface roughness becomes prominent when the film is stretched, and there is a tendency that it cannot serve as an outer layer.

  The thickness of the outermost layer needs to be greater than the size of the rough surface irregularities. Specifically, the transparency can be improved by setting the thickness to 1 μm or more, preferably 2 μm or more. Moreover, when providing slipperiness and heat-resistant fusion property, 3 micrometers or more are more preferable, and 4 micrometers or more are still more preferable. On the other hand, the upper limit of the thickness is preferably 25% or less, and preferably 20% or less of the entire film thickness. If it exceeds 25%, the film tends to become hard after shrinkage.

  By the way, it is preferable that the two outermost layers formed on the outer side of the film according to the present invention have the same thickness and the same composition from the viewpoints of shrinkage characteristics and curling prevention, but they are not necessarily the same.

  Furthermore, the film according to the present invention is not limited to the three-layer structure of the center layer and the two outermost layers, and has the center layer as one of the inner layers of the film, and as the outer layer on the surface. If it has the said outermost layer, unless the characteristic of this invention is inhibited, another inner layer may exist.

  Next, the film manufacturing method according to the present invention will be described. The method of forming a sheet from the resin mixture constituting the central layer and the polylactic acid polymer that is the resin constituting the outermost layer is to melt the resin mixture or resin with an extruder and, if necessary, extrusion A manufacturing method is generally used in which a predetermined amount of plasticizer is added by liquid addition from a vent groove or an injection groove in the middle of the machine and extruded. In extruding, existing methods such as a T-die method and a tubular method can be employed. At that time, it is necessary to set the temperature in consideration of a decrease in molecular weight due to decomposition.

  In addition, a plasticizer, a heat stabilizer, a light stabilizer, a light absorber, a lubricant, an inorganic filler, a colorant, a pigment, or the like may be added to the above resin mixture or resin for the purpose of adjusting various physical properties. Good.

  Examples of the plasticizer include dibutyl adipate, diisobutyl adipate, diisononyl adipate, diisodecyl adipate, di (2-ethylhexyl) adipate, di (n-octyl) adipate, di (n-decyl) adipate, dibutyl dicricol adipate, dibutyl Fatty acid ester plasticizers such as sebacate, di (2-ethylhexyl) sebacate, di (n-hexyl) azelate, di (2-ethylhexyl) azelate, di (2-ethylhexyl) dodecanedionate, diisononyl phthalate, diisodecyl phthalate, Examples thereof include phthalate ester plasticizers such as di (2-ethylhexyl) phthalate, and trimellitic acid ester plasticizers such as tri (2-ethylhexyl) trimellitate.

Next, the method for laminating the central layer and the outermost layer obtained by the above method is not particularly limited as long as the object of the present invention is not impaired, and examples thereof include the following four methods.
(1) A co-extrusion method in which two or three or more extruders are laminated with a multi-manifold or feed block type die and extruded as a molten sheet.
(2) A method of coating the other resin on one of the unrolled layers.
(3) A method of thermocompression bonding each layer at an appropriate temperature using a roll or a press.
(4) A method of bonding using an adhesive.

  The laminated film obtained by the above method is cooled with a cooling roll, air, water, etc., and then reheated by an appropriate method such as hot air, hot water, infrared rays, microwave, etc., and biaxially stretched. Examples of the biaxial stretching method include simultaneous biaxial stretching and sequential biaxial stretching. In terms of production equipment, simultaneous biaxial stretching is possible by the tubular method or tenter-type simultaneous biaxial stretching, and by sequentially stretching in the longitudinal direction by roll stretching and then stretching in the transverse direction by a tenter, sequential biaxial stretching. Is possible.

  Among these, the sequential biaxial stretching method in which the film is stretched in the longitudinal direction by roll stretching and then stretched in the transverse direction by a tenter is most commonly used. In the case of this method, when an aliphatic polyester having a high crystallinity is used, orientation crystallization proceeds at the time of roll stretching of the first axis, and stretching of the second axis becomes difficult. On the other hand, when the above aromatic aliphatic polyester is used, since the crystallinity is lower than that of the aliphatic polyester, the second axis can be stretched well by suppressing the orientation crystallization during the roll stretching of the first axis. Is possible.

  The stretching temperature needs to be changed depending on the resin mixing ratio, the crystallinity of the polylactic acid-based polymer, and the required use of the resulting heat-shrinkable film, but is generally controlled in the range of 70 to 95 ° C. The draw ratio needs to be changed according to the resin mixing ratio, the crystallinity of the polylactic acid polymer, and the required use of the heat-shrinkable film to be obtained. Then, the draw ratio is preferably 2 to 6 times.

  Further, the surface magnification is preferably 4 to 16 times, and preferably 9 to 15 times in consideration of the accuracy of the film thickness, the finish after shrinkage, and the like.

  Although the haze of the film obtained by the above method varies depending on the application, it is used for labeling for PET bottles and glass bottles. When transparency is very required by printing on the back side of the film, 10% The following is preferable, 7% or less is preferable, and 5% or less is more preferable. If it exceeds 10%, sufficient transparency may not be provided.

  Hereinafter, the present invention will be described in detail with reference to experimental examples and comparative examples, but the present invention is not limited thereto. In addition, the physical-property value and evaluation in an experiment example and a comparative example measured and evaluated by the following method. Here, the film take-up (flow) direction is described as MD, and the direction orthogonal thereto is described as TD.

[Measurement method and evaluation method]
[Heat shrinkage]
From the film, samples each having a 100 mm width marked line were cut out from MD and TD, immersed in an 80 ° C. hot water bath for 10 seconds, and the amount of shrinkage was measured. The thermal shrinkage rate was expressed as a percentage of the shrinkage amount relative to the original size before shrinkage.

[Natural shrinkage]
After leaving the film in a room at room temperature of 23 ° C. for 5 hours, a sample having a width in the MD direction of 50 mm and a width in the TD direction of 1000 mm was cut for measurement in the TD direction. Next, the sample was allowed to stand in a thermostatic chamber at room temperature of 30 ° C. for 30 days, and then the amount of shrinkage in the TD direction was measured. For the natural shrinkage, the ratio of the shrinkage to the original size before shrinkage was expressed as a% value. The natural shrinkage rate in the MD direction was measured in the same manner as in the TD direction. The evaluation in the table was judged according to the following criteria.
○: The natural shrinkage rate in any one of the MD direction and the TD direction is smaller than 1.5%. X: The natural shrinkage rate in both the MD direction and the TD direction is 1.5% or more.

[Tensile modulus]
The film was cut into a strip shape having a width of 5 mm and a length of 300 mm and manufactured by Toyo Seiki Co., Ltd .: Tensilon II type tensile tester at a temperature of 23 ° C. and a relative humidity of 50%. A tensile test was performed at min, and the strength and strain that were half the yield point strength were obtained and calculated.

[All haze]
The film was measured according to JIS K 7105.

[Fusing seal strength]
Using an L-type automatic packaging machine (manufactured by Hatanaka Co., Ltd .: HP-10Z), the fusing seal temperature and time are set at 185 ° C. and the instruction is 195 ° C. × 1.5 sec. A strip-shaped sample 15 mm × 100 mm long is cut out from the film so that it is perpendicular to the test length direction at the center, and is pulled at a distance between chucks of 40 mm and a pulling speed of 500 mm / min using an Intesco universal testing machine 205 type. The test was performed and the stress (N / 15 mm) at which the seal part breaks was measured.

[Shrink finish]
The obtained film is packaged using an L-type automatic packaging machine (manufactured by Hatanaka Co., Ltd .: HP-10Z), and the resulting package is shrink tunnel (manufactured by Hatanaka Co., Ltd .: HT-03310). It was immersed in a hot air tunnel at 115 ° C. for 5 to 7 seconds and shrink-wrapped. The finish after shrinkage was visually observed and evaluated according to the following criteria.
(1) Tight feeling ○: Adhering to the package,
X: There is a portion which is not in close contact with the package.
(2) Corner state ○: Soft,
X: Hard or stiff.

(raw materials)
[Aromatic aliphatic polyester]
-BASF Corporation: Ecoflex (terephthalic acid: 24 mol%, adipic acid 26 mol%, 1,4-butanediol: 50 mol%), hereinafter abbreviated as "Eco".
[Aliphatic polyester]
Polybutylene succinate: Showa High Polymer Co., Ltd .: Bionore 1030, hereinafter abbreviated as “BN”.

[Polylactic acid polymer]
Polylactic acid polymer 1: Cargill Dow Co., Ltd .: NatureWorks 4050, L-lactic acid / D-lactic acid = 94.5 / 5.5, weight average molecular weight: 200,000, hereinafter abbreviated as “PLA1”.
Polylactic acid polymer 2: Cargill Dow Co., Ltd .: NatureWorks 4060, L-lactic acid / D-lactic acid = 88.0 / 12.0, weight average molecular weight: 200,000 or less, abbreviated as “PLA2”.

[filler]
Silica: Mizusawa Chemical Co., Ltd .: Mizukasil P527, average particle size: 1.8 μm

(Examples 1-2, Comparative Examples 1-4)
Each resin is mixed in the ratio shown in Table 1 to adjust the resin mixture constituting the central layer, and each resin and silica are mixed in the ratio shown in Table 1 to adjust the resin mixture constituting the outermost layer. did. Next, the resin mixture of the center layer and the resin mixture of the outermost layer are kneaded at 190 to 210 ° C. in separate extruders and merged in a T-die at 200 ° C., and the outermost layer / center layer / outermost layer The melt composed of two types and three layers was quenched with a casting roll at about 36 ° C. to obtain an unstretched sheet. The unstretched sheet was stretched in the longitudinal direction under the conditions described in Table 1, and subsequently stretched in the width direction to obtain films shown in Table 1.
Said evaluation was performed using the obtained film. The results are shown in Table 1.
In Comparative Example 3, although the longitudinal direction (MD) could be stretched, breakage occurred in the width direction (TD). For this reason, the above evaluation was not performed.
Further, in Comparative Example 4, when an attempt was made to stretch in the longitudinal direction (MD), the sheet could not be stretched because the sheet was fused to the roll. For this reason, the extending | stretching of the width direction (TD) was not performed and said evaluation was not performed.

Claims (1)

The composition ratio of biodegradable aromatic aliphatic polyester and D-lactic acid and L-lactic acid is 98.0: 2.0 to 85.0: 15.0 or 2.0: 98.0 to 15.0. : A resin mixture with a polylactic acid polymer of 85.0,
50 to 90 mol% of the dicarboxylic acid component constituting the biodegradable aromatic aliphatic polyester is an aliphatic dicarboxylic acid,
A layer in which the content of the biodegradable aromatic aliphatic polyester is 70 to 90% by weight of the resin mixture is a center layer,
Polylactic acid system in which the constituent ratio of D-lactic acid and L-lactic acid is 95.0: 5.0 to 88.0: 12.0 or 5.0: 95.0 to 12.0: 88.0 A heat-shrinkable polylactic acid film having a polymer as the outermost layer.