JP3703795B2 - Polylactic acid-based biaxially stretched film with excellent fusing and sealing properties - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is a polylactic acid system for the purpose of packaging light weight items such as books, notebooks, calendars, direct mails, catalogs, etc., or packaging for foods such as vegetables, bread, and confectionery, clothing packaging, and general household goods. The biaxially stretched film relates to a polylactic acid-based biaxially stretched film that has high fusing seal strength and has excellent fusing and sealing properties having bag-making process stability free from whiskers and wrinkles.
[0002]
[Prior art]
Conventionally, films made of thermoplastic resins such as polyolefin and polyvinyl chloride have been used as packaging materials for foods, clothing and various miscellaneous goods. Among these, polyolefin resins having good heat sealability are suitable for bag making by fusing sealing. However, when these films are disposed in the natural environment, they do not decompose and accumulate as trash due to their chemical stability. In the future, it will become increasingly difficult to secure landfills and landfills. There are also concerns about adverse effects on the natural environment and wild animals.
[0003]
In place of these plastic films, a film made of polylactic acid has attracted attention as one of so-called biodegradable materials that can be harmlessly decomposed by hydrolysis and then microbial decomposition in soil. Polylactic acid is a plant-derived resin obtained by polycondensation of lactic acid obtained by fermenting various types of starch and saccharides. Ultimately, it is carbon dioxide and water, and is ideally recycled on a global scale. It has begun to be used for various applications as a resin.
[0004]
Therefore, as a packaging film made of a biodegradable resin, for example, Patent Document 1 discloses a stretched film made of a highly crystalline polylactic acid polymer and an aliphatic polyester having a Tg of 0 ° C. or less. Patent Document 2 discloses a packaging bag made of a crystalline polylactic acid polymer and having a film having a plane orientation index, a heat of crystal melting and a heat of crystallization at the time of temperature rise, and the like. . These are descriptions of a polylactic acid-based biaxially stretched film, but none of them has sufficient fusing and sealing properties, and the sealing strength is not stable during the fusing and sealing bag forming process.
[0005]
[Patent Document 1]
JP-A-9-157408 [0006]
[Patent Document 2]
Japanese Patent No. 3167595 [0007]
[Problems to be solved by the invention]
The present invention relates to a polylactic acid-based biaxially stretched film, which solves the above-described conventional problems, has a high fusing seal strength, and has a fusing and sealing property that has no bagging and wrinkle stability and is excellent in fusing and sealing properties. It is intended to provide a stretched film.
[0008]
[Means for Solving the Problems]
As a result of intensive studies to solve the above problems, the present inventors have arrived at the present invention. That is, the present invention is a polylactic acid-based biaxially stretched film comprising polylactic acid (A) and a copolyester (B), wherein the polylactic acid (A) comprises L-lactic acid and D-lactic acid, and L-lactic acid. / D-lactic acid = 100/0 to 80/20 (mol%), and the copolyester (B) is composed of an aromatic and aliphatic dicarboxylic acid component and an aliphatic diol component. ) And the copolymerized polyester (B) are (A) / (B) = 98/2 to 50/50, and the tensile elongation in the MD direction of the polylactic acid-based biaxially stretched film is 100 to 200. The polylactic acid-based biaxially stretched film excellent in fusing and sealing properties characterized by having a tensile modulus of 3.0 GPa or less. Moreover, this invention contains polylactic acid (A ') whose polylactic acid (A) is L-lactic acid / D-lactic acid = 94/6-80/20 (mol%) as the structural component, The inclusion The gist of the polylactic acid biaxially stretched film excellent in fusing and sealing properties, characterized in that the amount is 5 to 40% by mass of the whole film.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
The polylactic acid-based biaxially stretched film excellent in fusing and sealing properties of the present invention is a biaxially stretched film composed of polylactic acid (A) and copolymerized polyester (B).
[0010]
The polylactic acid (A) which is the main component constituting the film of the present invention is composed of poly-L-lactic acid whose structural unit is L-lactic acid, poly-D-lactic acid whose structural unit is D-lactic acid, L-lactic acid and D-lactic acid. It consists of poly DL-lactic acid which is a copolymer with lactic acid, or a mixture thereof.
The ratio of L-lactic acid and D-lactic acid (L-lactic acid / D-lactic acid) constituting the polylactic acid (A) needs to be 100/0 to 80/20 (mol%). When the ratio of L-lactic acid and D-lactic acid constituting the polylactic acid is within this range, it is possible to perform a fusing seal at a low temperature, and the good characteristics that the seal portion is easily stretched and stress concentration hardly occurs are enhanced.
[0011]
The number average molecular weight of the polylactic acid (A) is preferably in the range of 50,000 to 300,000, more preferably 80,000 to 150,000. When the number average molecular weight is 50,000 or less, the resulting film has insufficient mechanical strength, and also frequently undergoes cutting during the stretching and winding processes, resulting in a decrease in operability. On the other hand, when the number average molecular weight exceeds 300,000, the fluidity at the time of heating and melting becomes poor and the film-forming property is lowered.
[0012]
As a polymerization method for obtaining polylactic acid, any of a condensation polymerization method and a ring-opening polymerization method can be adopted, and a small amount of chain extender such as a diisocyanate compound, diepoxy compound, An acid anhydride or the like may be used.
[0013]
The copolyester (B) constituting the film of the present invention together with the polylactic acid (A) refers to a copolyester composed of an aromatic and aliphatic dicarboxylic acid component and an aliphatic diol component. Among dicarboxylic acid components, aromatic dicarboxylic acids include terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid, etc., and aliphatic dicarboxylic acids include succinic acid, adipic acid, suberic acid, sebacic acid, dodecanediic acid, dimer An acid etc. are mentioned. Examples of the aliphatic diol include ethylene glycol, propylene glycol, 1,4-butanediol, cyclohexanedimethanol, and an ethylene oxide adduct of bisphenol A having alcoholic hydroxyl groups at both ends. Preferable specific examples of the copolyester (B) include copolyesters in which the aliphatic component is adipic acid and 1,4-butanediol and the aromatic component is terephthalic acid.
[0014]
In addition, you may introduce | transduce a urethane bond, an amide bond, an ether bond, etc. into the copolymerization polyester (B) in the range which does not affect biodegradability. Moreover, you may add a lubricant from the surface of the handling in a manufacturing process or a secondary processing process, and film runnability. As a lubricant, a stable metal oxide such as silica, titanium dioxide, talc, and alumina, a stable metal salt such as calcium carbonate, calcium phosphate, and barium sulfate, or a so-called organic system made of an organic resin that is inert to polylactic acid. Beads can be suitably used. Any one of these lubricants may be used alone, or two or more may be used in combination.
[0015]
The mass ratio (A / B) of the polylactic acid (A) and the copolyester (B) constituting the film of the present invention needs to be 98/2 to 50/50. If the content of the polylactic acid (A) exceeds this range, the film becomes too strong, that is, the tensile modulus of the film becomes high, so that stress concentrates on the fusing seal part and the bag is easily broken. That is, the melted seal portion is poorly stretched. Further, if the content of the copolymerized polyester (B) exceeds this range, the flexibility of the film increases, but the operability including stretchability and slipperiness is deteriorated, and the film is easily stretched too much. Sometimes wrinkles and whiskers increase, resulting in poor seal appearance. By setting the mass ratio (A / B) of the polylactic acid (A) and the copolymerized polyester (B) within the above range, the tensile elongation of the film in the MD direction is set to 100 to 200% and the tensile elastic modulus is set to 3. It can be controlled to 0 GPa or less, and it is possible to improve and stabilize the fusing seal strength, increase the speed at the time of bag making, and the like.
[0016]
The film of the present invention comprises a polylactic acid (A) and a copolymerized polyester (B), and the polylactic acid (A) has, as its constituent components, a ratio of L-lactic acid to D-lactic acid (L-lactic acid / D It is preferable to contain 5-40 mass% polylactic acid (A ') whose -lactic acid is 94 / 6-80 / 20 (mol%) in a film. When the content of the polylactic acid (A ′) in the film is less than 5% by mass, bag making is possible, but the effect of increasing the seal strength and the seal elongation is small, and when the content exceeds 40% by mass. Shrinkage wrinkles become remarkable and the appearance may be impaired.
[0017]
Since the polylactic acid-based biaxially stretched film of the present invention has the above-described configuration, it has excellent fusing and sealing properties. As specific fusing sealability, it is preferable that the fracturing seal portion has a tensile rupture strength (fusing seal strength) of 10 N / cm or more and a rupture elongation of 5 to 50%. Further, the fracturing seal portion has a tensile rupture strength. Is more preferably 15 N / cm or more and the elongation at break is 20 to 50%. When the film has such a fusing sealing property, it is difficult to break a relatively heavy magazine or calendar content such as a calendar, and it is a highly practical bag. Can be realized.
[0018]
In the polylactic acid-based biaxially stretched film of the present invention, a pigment, an antioxidant, a plasticizer, an ultraviolet absorber, a lubricant, a crystal nucleating agent, an antistatic agent, etc. are added or coated on the surface as needed. be able to. The thickness of the polylactic acid-based biaxially stretched film of the present invention is not particularly limited, and may be appropriately set depending on the application, required performance, price and the like. In general, a thickness of about 10 to 100 μm is appropriate.
[0019]
Below, an example is given and demonstrated about the manufacturing method of the polylactic acid-type biaxially stretched film of this invention.
[0020]
Examples of the method for producing the polylactic acid-based biaxially stretched film of the present invention include a T-die method, an inflation method, a calendar method, and the like. When manufactured by the T-die method, polylactic acid (A), copolyester (B), and a polylactic acid resin composition containing appropriate amounts of a lubricant, an antistatic agent, and a plasticizer, if necessary, are added to an extruder. For example, melt kneading is performed at a cylinder temperature of 180 to 250 ° C. and a T die temperature of 200 to 250 ° C., and cooling is performed with a cooling roll controlled to 20 to 40 ° C. to obtain an unstretched sheet having a thickness of 100 to 500 μm.
[0021]
As a biaxial stretching method for the unstretched sheet, any of a simultaneous biaxial stretching method using a tenter method and a sequential biaxial stretching method using a metal roll tenter may be used. For example, when an unstretched film is formed into a film by a sequential biaxial stretching method, the obtained unstretched film is stretched in the machine direction at a roll surface temperature of 50 to 80 ° C. according to the rotational speed ratio of the drive roll, and continuously. The film is stretched in the transverse direction at a stretching temperature of 70 to 100 ° C. The stretching ratio is not particularly limited, but considering the mechanical properties of the film, at least the longitudinal stretching ratio is preferably 2.5 times or more, and the surface magnification is preferably 8 times or more. If the longitudinal and lateral draw ratios are less than 2.5, sufficient mechanical properties cannot be obtained, resulting in poor practicality. The upper limit of the draw ratio is not particularly limited, but if it exceeds 8 times, film breakage tends to occur. Therefore, the length and width are preferably 2.5 times or more and 8 times or less, and the length draw ratio is 2 It is preferable that it is 0.5 to 5.0 times and the transverse draw ratio is 2.5 to 8.0 times. After the above stretching treatment is performed, a heat treatment is performed at a temperature of 100 to 150 ° C., and a thermal relaxation treatment is performed under conditions of a relaxation rate of 2 to 8%.
[0022]
In order to produce a packaging bag for food or industry from the film produced as described above, bag making by fusing seal is performed. Bag making by fusing seal is, for example, sending a long strip of film in half-fold in the width direction, using a rotating ring-shaped sealing blade, a heat transfer wire that moves up and down, and a fusing blade along the film conveyance direction. Is performed by fusing and sealing in the width direction of the film with an interval of.
The obtained packaging bag has a high strength of the fusing seal part as described above, and also has a good appearance with reduced wrinkles due to heat shrinkage, etc., so it can be used for packaging food, clothing and various products. It can be suitably used as a bag.
[0023]
【Example】
EXAMPLES Next, although an Example demonstrates this invention, this invention is not restrict | limited by the following Example. In addition, the measurement of the various physical-property values in an Example and a comparative example was implemented with the following method.
[0024]
(1) Tensile elongation and tensile modulus:
In accordance with the method described in ASTM-D882, measurement was performed with an autograph manufactured by Shimadzu Corporation using a sample having a length of 100 mm and a width of 10 mm. In the present invention, one having a tensile elongation in the MD direction of 100 to 200% and a tensile modulus of 3.0 GPa or less is regarded as acceptable.
[0025]
(2) Tensile breaking strength and breaking elongation of the fusing seal part:
Using a three-way side sealing machine (HK-40V, manufactured by Totani Giken Kogyo Co., Ltd.) equipped with a hot blade with a blade angle of 90 °, a seal part of a bag made at a sealing temperature of 380 ° C., a pitch of 200 mm, and a shot number of 100 rpm Then, a test piece having a seal width of 15 mm was cut out and subjected to a tensile test by 180 ° peeling at a tensile speed of 300 mm / min.
[0026]
(3) Packaging bag evaluation:
A packaging bag was prepared by the method described above, and a product having a good seal portion appearance was marked with ◯, and a wrinkle or whiskers with poor appearance was marked with ×.
[0027]
Comparative Example A
As polylactic acid (A), polylactic acid (L-lactic acid / D-lactic acid = 98.5 / 1.5 (mol%), melting point 165 ° C., number average molecular weight 105000) manufactured by Cargill Dow Polymer Co., Ltd. (A-1) ) 95 parts by mass, as copolymerized polyester (B), 5 parts by mass by Eastman Chemical Co., Ltd. Ester Bio Ultra (B-1), as an anti-blocking agent, amorphous silica (manufactured by Fuji Silysia Chemical, Silicia 310P, average particle size is 1.4 μm) A polylactic acid resin composition containing 0.1 part by mass was melt-extruded at a T-die temperature of 230 ° C. with a 90 mmφ single-screw extruder, and then closely adhered to a cast roll whose temperature was controlled at 20 ° C. An unstretched film having a thickness of 230 μm was prepared. The obtained unstretched film is guided to a simultaneous biaxial stretching machine, and in the stenter, simultaneous biaxial stretching of 3.0 × 3.0 times is performed at a preheating temperature of 78 ° C. and a stretching temperature of 75 ° C. The film was heat-set at 125 ° C. for 10 seconds with a relaxation rate of 5% to obtain a biaxially stretched film having a thickness of 25 μm.
The obtained film is half-folded in the width direction so that an adhesive margin of 20 mm appears on one side, and in the MD direction of the film so that the adhesive margin portion becomes the opening and the half-fold portion becomes the bottom of the packaging bag. At a temperature of 380 ° C. with a predetermined interval, a fusing seal was performed at a shot number of 100 rpm in the TD direction to produce a packaging bag having a length of 250 mm and a width of 200 mm. Table 1 shows the physical properties of the obtained film and the packaging bag.
[0028]
Example 1
As polylactic acid (A-1) 60 parts by mass, polylactic acid (A ′), polylactic acid (L-lactic acid / D-lactic acid = 88/12 (mol%) manufactured by Cargill Dow Polymer, no melting point, number average A polylactic acid resin composition containing 10 parts by mass of molecular weight 95000) (A-3), 30 parts by mass of copolymer polyester (B-1), and 0.1 parts by mass of amorphous silica was added to a 90 mmφ single screw extruder. Then, it was melt-extruded at a T-die temperature of 220 ° C., and was tightly cooled by close contact with a cast roll whose temperature was controlled at 20 ° C. to produce an unstretched film having a thickness of 230 μm. The obtained unstretched film is guided to a simultaneous biaxial stretching machine, and in the stenter, simultaneous biaxial stretching of 3.0 × 3.0 times is performed at a preheating temperature of 76 ° C. and a stretching temperature of 74 ° C., and then in the transverse direction. The film was heat-set at 125 ° C. for 10 seconds with a relaxation rate of 5% to obtain a biaxially stretched film having a thickness of 25 μm. Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0029]
Example 2
70 parts by mass of polylactic acid (A-2) (manufactured by Cargill Dow Polymer, L-lactic acid / D-lactic acid = 96.0 / 4.0 (mol%), melting point 150 ° C., number average molecular weight 105000), poly Polylactic acid resin containing 10 parts by mass of lactic acid (A-3), 20 parts by mass of copolyester (B-2) (manufactured by BASF, Ecoflex F, melting point 105 ° C.) and 0.1 part by mass of amorphous silica The composition was melt-extruded at a T-die temperature of 220 ° C. using a 90 mmφ single-screw extruder, and was closely adhered and rapidly cooled to a cast roll whose temperature was controlled at 20 ° C. to produce an unstretched film having a thickness of 230 μm. The obtained unstretched film is guided to a simultaneous biaxial stretching machine, and in the stenter, simultaneous biaxial stretching of 3.0 × 3.0 times is performed at a preheating temperature of 78 ° C. and a stretching temperature of 76 ° C., and then in the transverse direction. The film was heat-set at 115 ° C. for 10 seconds with a relaxation rate of 5% to obtain a biaxially stretched film having a thickness of 25 μm. Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0030]
Example 3
A 250 μm unstretched film extruded and formed in the same manner as in Comparative Example A with the resin composition shown in Table 1 was stretched 2.5 times in the longitudinal direction at a preheating roll of 65 ° C. and a stretching roll of 74 ° C., and subsequently The film was stretched 4.0 times in the transverse direction at a stretching temperature of 82 ° C., and then subjected to a heat setting treatment at 120 ° C. for 10 seconds at a transverse relaxation rate of 7% to obtain a biaxially stretched film having a thickness of 25 μm. Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0031]
Example 4
A 310 μm unstretched film extruded and formed in the same manner as in Comparative Example A with the resin composition shown in Table 1 was stretched 2.8 times in the longitudinal direction at a preheating roll 68 ° C. and a stretching roll 76 ° C., and subsequently The film was stretched 4.5 times in the transverse direction at a stretching temperature of 86 ° C., and then subjected to a heat setting treatment at 120 ° C. for 10 seconds at a transverse relaxation rate of 7% to obtain a biaxially stretched film having a thickness of 25 μm. Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0032]
Comparative Examples 1-3
A biaxially stretched film having a thickness of 25 μm was obtained in the same manner as in Comparative Example A except that the resin composition shown in Table 1 was used. Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0033]
Comparative Example 4
Polylactic acid (A-4) (manufactured by Cargill Dow Polymer, L-lactic acid / D-lactic acid = 78.0 / 22.0 (mol%), no melting point, number average molecular weight 85000) 95 parts by mass, copolymer Using a polylactic acid resin composition containing 5 parts by mass of polyester (B-1) and 0.1 parts by mass of amorphous silica, a biaxially stretched film having a thickness of 25 μm was obtained in the same manner as in Example 3 . Table 1 shows the physical properties of the packaging bags produced in the same manner as in Comparative Example A.
[0034]
Comparative Example 5
A 310 μm unstretched film extruded and formed in the same manner as in Comparative Example A with the resin composition shown in Table 1 was stretched 2.8 times in the longitudinal direction at a preheating roll 53 ° C. and a stretching roll 70 ° C., and subsequently The film was stretched 4.5 times in the transverse direction at a stretching temperature of 80 ° C., and then subjected to heat setting at 120 ° C. for 10 seconds at a transverse relaxation rate of 7% to obtain a biaxially stretched film having a thickness of 25 μm. Since the copolymerized polyester (B-2) is contained in a large amount and the polylactic acid (A-3) exceeds the polylactic acid (A-2), uneven kneading or stretch cutting, that is, fusing is caused. Could not be collected.
[0035]
[Table 1]
[0036]
The polylactic acid-based biaxially stretched films of the present invention represented by the examples all have good operability and thickness accuracy at the time of film production, and whisker, shrinkage wrinkles, etc. even when bag making by fusing seal is carried out Did not occur and had high sealing strength.
On the other hand, polylactic acid-based biaxially stretched films that do not satisfy the present invention, represented by comparative examples, cause deterioration in operability (cutting and thickness accuracy) during film production, or lack of fusing seal strength and poor seal appearance (whiskers). Caused shrinkage wrinkles). That is, in the comparative example 1, although the bag obtained from this film looks good, since the mass ratio of the copolyester (B) is small, the seal strength and the seal elongation are low and the practicality is poor. In Comparative Example 2, the bag obtained from this film has increased flexibility because the mass of the copolyester (B) exceeds the mass of polylactic acid (A), but the operability including stretchability and slipperiness is improved. make worse. In addition, since the film stretches too easily, wrinkles and whiskers increase during bag making, resulting in poor seal appearance. In Comparative Example 3, since the copolymer polyester (B) is not contained, the bag obtained from this film has remarkable generation of whiskers and shrinkage wrinkles, and has low seal strength and seal elongation, so that it is not practical. In Comparative Example 4, since L-lactic acid / D-lactic acid of polylactic acid (A) was 78/22, not only shrinkage wrinkles and whiskers were generated, but also the seal strength was insufficient.
[0037]
【The invention's effect】
According to the present invention, polylactic acid (A) is composed of L-lactic acid / D-lactic acid = 100/0 to 80/20 (mol%), and copolymer polyester (B) is aromatic and aliphatic. A polylactic acid system comprising a dicarboxylic acid component and an aliphatic diol component, wherein the mass ratio of polylactic acid (A) to copolymerized polyester (B) is (A) / (B) = 98/2 to 50/50 By setting it as a biaxially stretched film, the polylactic acid type biaxially stretched film which can raise the elongation of MD direction and can reduce an elasticity modulus and has high fusing seal strength without a beard and a wrinkle is obtained. A packaging bag made of such a film can be easily produced by fusing seal, has high fusing seal strength, and has a good sealing appearance with reduced whiskers and wrinkles. It can be suitably used as a packaging bag for products.

Claims (1)

A polylactic acid biaxially stretched film comprising a polylactic acid (A) and a copolyester (B), wherein the polylactic acid (A) comprises L-lactic acid and D-lactic acid, L-lactic acid / D-lactic acid = 100/0 to 80/20 (mol%), the copolymer polyester (B) is composed of an aromatic and aliphatic dicarboxylic acid component and an aliphatic diol component, and is copolymerized with polylactic acid (A) The mass ratio with (B) is (A) / (B) = 98/2 to 50/50, and polylactic acid (A) is L-lactic acid / D-lactic acid = 94/6 to The polylactic acid (A ') which is 80/20 (mol%) is contained, the content is 5-40 mass% of the whole film, and the tensile elongation of MD direction of a polylactic acid-type biaxially stretched film is 100. was 200%, and tensile modulus der less 3.0GPa , Polylactic acid biaxially stretched film excellent in fusing sealability, wherein the tensile strength of the heat-sealing portion is at 15N / cm or more and breaking elongation of 20 to 50%.