JP2003072010A - Heat-shrinkable polylactic acid type film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a heat-shrinkable polylactic acid type film having proper heat shrinkability, excellent in heat sealability and suitable for overlapping packaging. SOLUTION: The heat-shrinkable polylactic acid type film has a substrate layer and the heat seal layer provided on the surface of the substrate layer. The substrate layer is formed of a polylactic acid film of which the heat shrinkage factor is 5-10% in an MD direction and 5% or less in a TD direction. The heat seal layer is formed from a film containing a biodegradable polymer of which the melting point or softening point is lower than that of polylactic acid forming the substrate layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a heat-shrinkable polylactic acid-based film, and is particularly used for snack food cases, pharmaceutical cases, magnetic tapes, magnetic disks, and other individual packaging or overwrapping applications suitable for integrated packaging. , A heat-shrinkable polylactic acid-based film having excellent heat-shrinkability and heat-sealing property.

[0002]

2. Description of the Related Art Polyethylene terephthalate stretched film, polypropylene stretched film and the like are known as films having excellent mechanical strength, heat resistance and dimensional stability, and are widely used in industry.

However, when these plastic films are disposed in the natural environment, they are not decomposed due to their scientific stability, but are accumulated as garbage. In the future, it is becoming more and more difficult to secure landfills and landfills, and there are concerns about problems such as adversely affecting the natural environment and wild animals. Instead of these plastic films, polylactic acid films are ones that can be hydrolyzed in soil and then converted into harmless decomposition products by microbial decomposition.

An unstretched film or sheet of polylactic acid is a material having low strength and elongation and poor impact resistance, and as such is not practical as a molded product. However, it is possible to improve the brittleness by uniaxially or biaxially stretching and orienting it, and the stretched polylactic acid film is used for information recording materials (magnetic cards), industrial packages, agricultural mulch films, etc. Some of them have been put to practical use.

However, in these polylactic acid-based stretched films, a film represented by a polypropylene-based biaxially stretched film having both heat-sealing property and heat-shrinking property, that is, a practically used as a so-called low heat-shrinkable overlapping wrapping film. Is rarely seen.

The heat-shrinkable biaxially stretched film is described in JP-A-7-256753 and JP-A-9-187863. However, these are both related to the heat-shrinkable biaxially stretched film made of polylactic acid-based polymer, both are films having a high shrinkage rate used for applications such as plastic bottle binding, It does not have a low level of heat shrinkability suitable as the film for overlapping, and also does not have heat sealability. Therefore, at present, there is a strong demand for a biodegradable film that can replace the biaxially stretched polypropylene film that is widely used as an overlapping film having both heat shrinkability and heat sealability.

[0007]

DISCLOSURE OF THE INVENTION The present invention provides a heat-shrinkable polylactic acid-based film having an appropriate heat-shrinkability and an excellent heat-sealing property, which is suitable for use in overlapping packaging. With the goal.

[0008]

Means for Solving the Problems The inventors of the present invention have made it possible to obtain a resin composition, a stretching temperature, a stretching ratio,
We found that by adjusting the heat treatment temperature, relaxation rate, and surface treatment appropriately, we obtained a polylactic acid-based film with appropriate heat shrinkability, and formed a layer of heat-sealing material on the surface of the base film, that is, the substrate layer. Found that the required heat sealing properties can be achieved by
The present invention has been completed.

That is, the present invention is a heat-shrinkable polylactic acid-based film having a laminated structure, wherein the base material layer formed of the polylactic acid-based film and the polylactic acid forming the base material layer have a melting point or softening point higher than that of the polylactic acid-based film. And a heat-sealing layer formed as an outermost layer by a film containing a low biodegradable polymer, and having a heat shrinkage ratio at 100 ° C. of M.
The heat-shrinkable polylactic acid-based film is characterized by being 5 to 10% in the D direction and 5% or less in the TD direction.

As a result, the base material layer has appropriate heat shrinkability, biodegradability, and the heat seal layer having biodegradability provides the required heat sealability. A heat-shrinkable polylactic acid-based film suitable for use in wrapping packaging can be provided.

[0011]

BEST MODE FOR CARRYING OUT THE INVENTION The heat-shrinkable film of the present invention is suitable for overlapping packaging and the like, so that the heat shrinkage at 100 ° C. is 5 to 10% in the MD direction and 5% in the TD direction.
It must be: In the present invention, the heat shrinkage rate is controlled within the above range by using a specific polymer and appropriately setting the film production conditions such as the stretching temperature, the stretching ratio, the heat treatment temperature, and the relaxation rate in accordance with the resin properties. can do.

The heat shrinkage in the MD direction, that is, the machine direction is 1
If it exceeds 0%, shrinkage wrinkles are likely to occur during the heat-shrink packaging process, and the heat-bonded portion is likely to peel off. When the heat shrinkage in the MD direction is less than 5%, sufficient heat shrinkability cannot be obtained, and the appearance after packaging does not have a tight feeling and has no commercial value. Further, if the heat shrinkage in the TD direction, that is, the direction perpendicular to the machine direction exceeds 5%, printing deviation occurs in secondary processing such as printing or coating, and the aesthetic appearance is significantly impaired.

The polylactic acid-based polymer forming the base layer film may be any polylactic acid or one having a lactic acid component as a main component, such as polylactic acid, lactic acid or lactide and other hydroxycarboxylic acid or dicarboxylic acid. , Diols, copolymers with cyclic lactones, and blends. A urethane bond, an amide bond, an ether bond, or the like can be introduced into these as long as the biodegradability is not affected. Specifically, as polylactic acid, poly L-lactic acid in which the structural unit of lactic acid is L-lactic acid, and the structural unit is D-
Examples thereof include poly D-lactic acid which is lactic acid, poly DL-lactic acid which is a copolymer of L-lactic acid and D-lactic acid, or a mixture thereof. The number average molecular weight is preferably in the range of 50,000 to 300,000, more preferably 80,000 to 150,000. If the number average molecular weight is less than 50,000, the mechanical strength of the obtained film will be insufficient, and cutting will frequently occur during the stretching and winding steps, 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 formability deteriorates.

The heat seal layer constituting the film of the present invention is formed of a film containing a biodegradable polymer having a lower melting point or softening point than the polylactic acid forming the base material layer.

Examples of the film containing such a biodegradable polymer include a film containing at least one of an aliphatic polyester, an aliphatic-aromatic copolyester, and a polyester carbonate. That is, these polymers can be used alone or in an arbitrary blended state.

The aliphatic polyester contains polylactic acid. When the heat seal layer is made of polylactic acid, its melting point or softening point can be lowered by copolymerization. Specifically, as the polylactic acid-based film constituting the heat-sealing layer, a homopolymer to which a copolymerization component such as D-lactic acid or L-lactic acid, glycolic acid or 6-hydroxycarboxylic acid is added is used. As a result, the melting point can be lower than that of the base material layer. Also,
In order to impart flexibility to the heat seal layer, a plasticizer may be added to the polylactic acid forming the heat seal layer. When the copolymerization ratio is increased, the heat seal layer can be formed of an amorphous polylactic acid film.

As the aliphatic polyester suitable for the heat-sealing layer, in addition to the above-mentioned polylactic acid, a homopolymer or copolymer of hydroxycarboxylic acid other than L-lactic acid or D-lactic acid, and aliphatic (also alicyclic) Including the same below) a polymer having a dicarboxylic acid unit and an aliphatic diol unit as main components, and a block copolymer of these aliphatic polyesters and the above polylactic acid-based polymer, and the above-mentioned aliphatic dicarboxylic acid unit and It is preferably a polymer containing an aliphatic diol unit as a main component.

The hydroxycarboxylic acid used in the homopolymer or copolymer of hydroxycarboxylic acid other than L-lactic acid or D-lactic acid is glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid or 2-hydroxybutyric acid. Hydroxy-
n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2
-Hydroxy-3-methylbutyric acid, 2-hydroxyvaleric acid, 2-methyllactic acid, 2-hydroxycaproic acid and the like can be mentioned.

Examples of the above-mentioned polymer containing an aliphatic dicarboxylic acid unit and an aliphatic diol unit as main components include, for example, polyethylene succinate, polyethylene adipate, polyethylene suberate, polyethylene sebacate, polyethylene decanedicarboxylate, polybutylene. Examples thereof include succinate, polybutylene adipate, polybutylene sebacate, and copolymers thereof. Among them, polybutylene succinate and polybutylene succinate adipate are preferably used.

As described above, in the present invention, a block copolymer of a polylactic acid-based polymer and an aliphatic polyester (a partial transesterification product thereof, a product containing a small amount of a chain extender residue) Can also be used).
This block copolymer can be prepared by any method.

The aliphatic-aromatic polyester may be any one having an aliphatic component and an aromatic component,
For example, hydroxycaproic acids such as lactic acid, glycolic acid, hydroxybutyric acid and hydroxycaproic acid, cyclic lactones such as caprolactone, butyrolactone, lactide and glycolide, ethylene glycol, butanediol,
Cyclohexanedimethanol, bis-hydroxymethylbenzene, toluenediol and other diols, succinic acid, adipic acid, suberic acid, sebacic acid, terephthalic acid, isophthalic acid, naphthalenedicarboxylic acid and other dicarboxylic acids, cyclic acid anhydrides, oxiranes As a component,
Examples thereof include a copolymer having an aliphatic component and an aromatic component. Among them, a copolyester having 1,4-butanediol and adipic acid as an aliphatic component and terephthalic acid as an aromatic component is preferable. Further, a urethane bond, an amide bond, an ether bond or the like can be introduced as long as it does not affect the biodegradation.

As the polyester carbonate, those obtained by reacting a dihydroxy compound with a dicarboxylic acid or its alkyl ester or a dihydroxy compound with a carbonic acid diester can be used.

Examples of the dihydroxy compound include ethylene glycol, trimethylene glycol, tetramethylene glycol, butanediol, pentanediol, propylene glycol, hexamethylene glycol, neopentyl glycol, toluene diol and bis-hydroxymethylbenzene. Among them, 1,
It is preferable to use 4-butanediol as one of the components. Examples of the dicarboxylic acid include malonic acid, glutaric acid, adipic acid, azelaic acid, terephthalic acid,
Isophthalic acid, naphthalenedicarboxylic acid and the like can be appropriately used in combination. Above all, it is preferable to use succinic acid as one of the components. The dihydroxy compound and dicarboxylic acid may be esters or acid anhydrides thereof. Further, the dihydroxy compound and the dicarboxylic acid can be used individually or as a mixture and can be combined in a desired manner, but in the present invention, they have appropriate biodegradability and have practical heat resistance. A high melting point is preferable. The dihydroxy compound preferably contains 1,4-butanediol and succinic acid as the dicarboxylic acid. Examples of carbonic acid diesters include dimethyl carbonate, diethyl carbonate, diisopropyl carbonate, dibutyl carbonate, diphenyl carbonate, ditolyl carbonate, bis (chlorophenyl) carbonate, and m.
-Cresyl carbonate and the like can be mentioned, and among them, diphenyl carbonate is particularly preferable.

The film forming the heat seal layer can be formed of a blend of polylactic acid and a biodegradable polymer having a lower melting point or softening point than the polylactic acid. In this case, the blending ratio is (polylactic acid) / (biodegradable polymer) = 90/10 to 0/10 by mass ratio.
It is preferably 0. Polylactic acid of 0% by mass and biodegradable polymer of 100% by mass means that the film forming the heat-sealing layer is formed only of the biodegradable polymer having a lower melting point or softening point than that of polylactic acid. Means that

The melting point or softening point of the biodegradable polymer forming the heat seal layer is such that the base layer is formed in order to exhibit the required heat seal performance without causing thermal damage to the base layer. 10 ℃ above the melting or softening point of polylactic acid
It is preferably lower, and more preferably 25 ° C. or higher.

A biodegradable polymer having a lower melting point or softening point than polylactic acid has a heat of crystal fusion of 40 when heated.
It is preferably J / g or less, more preferably 30 J / g or less. This makes it possible to provide excellent heat-sealing properties, particularly heat-sealing properties at low temperatures.

The heat-sealing strength when the heat-sealing layers of the film are laminated and bonded to each other is 7 N /
When it is at least cm, practically sufficient heat sealing performance can be achieved. It is more preferable that it is 10 N / cm or more.

The film of the present invention may have a constitution in which the outermost heat-sealing layer is adhered to one surface of the base material layer via an adhesive layer. Alternatively, heat seal layers can be formed on both sides of the base material layer. Furthermore, a barrier layer may be interposed between the base material layer and the heat seal layer.

A film having a heat-sealing layer formed on both sides of a base material layer is formed by, for example, rolling the film into a cylindrical bag shape and superposing both ends on the front side and the back side, and heat-sealing the superposed portion. It can be applied in any case.

As the adhesive for adhering the base material layer and the heat seal layer, vinyl-based, acrylic-based, polyamide-based, polyester-based, rubber-based and urethane-based adhesives are preferable. From the viewpoint of biodegradability, polysaccharides such as starch, amylose and amylopectin, proteins and polypeptides such as glue, gelatin, casein, zein and collagen, natural materials such as unvulcanized natural rubber and fats Aromatic polyesters, aliphatic-aromatic copolymer polyesters, aliphatic polyester urethanes, aliphatic polyester-modified polyvinyl alcohol vinyl acetate copolymers and the like are preferable.

When the base material layer and the heat seal layer are laminated without using an adhesive, the respective polymers are melted and kneaded by a plurality of extruders, and then, in a die or in a feed block before that. A method of laminating and co-extruding, a method of coating on the unwound film,
Examples thereof include a method of thermocompression bonding a plurality of films with a roll or a press.

The thickness of the film of the present invention is not particularly limited and may be appropriately set depending on the use, the required performance, the price, etc. Generally, a thickness of about 10 to 200 μm is suitable.

In the film of the present invention, additives such as a crystal nucleating agent, a plasticizer, a lubricant, an inorganic filler and an ultraviolet absorber, a modifier, a cross-linking agent, or the like are used for the purpose of adjusting the physical properties and processability of the film. It is also possible to add a polymer material of the above.

As the plasticizer, those having excellent compatibility with the polymer forming the film are preferable, and specifically, the aliphatic polycarboxylic acid ester derivative, the aliphatic polyhydric alcohol ester derivative, and the aliphatic oxy compound are used. Acid ester derivative,
A single or a plurality of mixtures selected from aliphatic polyether derivatives, aliphatic polyether polycarboxylic acid ester derivatives and the like can be mentioned.

As the lubricant, aliphatic carboxylic acid amides such as stearic acid amide, oleic acid amide, erucic acid amide and behenic acid amide are preferable. As the inorganic filler, natural or synthetic silicate compounds, titanium oxide, barium sulfate, calcium phosphate, calcium carbonate, sodium phosphate, silica, zeolite, aluminum oxide, magnesium carbonate and the like are preferable. Examples of the silicate compound include layered silicates such as kaolinite, halloysite, talc, smectite, vermiculite and mica. These layered silicates may be swellable or non-swellable, and may be surface-treated.

In the present invention, as a polymerization method for obtaining a biodegradable polymer such as polylactic acid, either a condensation polymerization method or a ring-opening polymerization method can be adopted. It is also possible to adopt a method of further advancing the polymerization by adding one or more sub-components such as other polymer, monomer and oligomer components during or immediately after the polymerization. Also,
It does not matter at any stage of the polymerization, but a small amount of a chain extender for the purpose of increasing the molecular weight, for example, a diisocyanate compound,
You may use an epoxy compound, an acid anhydride, etc.

Examples of the method for producing the heat-shrinkable polylactic acid-based film of the present invention include a T-die method, an inflation method, a calender method, and the like. The T-die method is a method in which a polymer is melt-kneaded and extruded using a T-die. preferable.

For example, when the base material layer is produced by the T-die method, a resin composition prepared by adding an appropriate amount of additives to a polylactic acid polymer is supplied to an extruder hopper,
Extruder, for example, the cylinder temperature 160 ~ 260 ℃, T
Die temperature is heated to 180-250 ° C, melt-kneaded, extruded, and cooled by a cooling roll controlled at 20-40 ° C.
An unstretched sheet having a thickness of 100 to 500 μm is obtained.

The obtained unstretched sheet is biaxially stretched in principle. As a method therefor, a simultaneous biaxial stretching method by a tenter system, a sequential biaxial stretching method by a roll and a tenter can be adopted. . For example, when the film is stretched by the sequential biaxial stretching method, first,
The unstretched sheet is stretched in the machine direction according to the rotation speed ratio of the rolls. At this time, it is preferable to set the roll surface temperature to 50 to 80 ° C. and the draw ratio to 2.0 to 4.0 times, respectively. Then, it is continuously stretched in the transverse direction at a stretching temperature of 70 to 100 ° C. and a stretching ratio of 2.5 to 8.0 times. After that, it is preferable to perform heat treatment at a temperature of 100 to 150 ° C. and heat relaxation treatment under a condition of a relaxation rate of 2 to 8%.
The heat-shrinkable polylactic acid-based film obtained by forming the base material layer with the film produced under such conditions,
5% to 10% heat shrinkage at 100 ° C in MD and TD
It can be 5% or less in the direction.

Similarly, the heat-sealing layer can be obtained by subjecting it to film formation and stretching treatment. In addition, an unstretched film is preferable in order to obtain particularly excellent heat sealability. Then, the base material layer and the heat seal layer thus obtained are adhered to each other, for example, via an adhesive as described above, whereby it is possible to obtain an integrated film by laminating both.

As described above, according to the present invention, since the base material layer has an appropriate heat shrinkability and the heat seal layer has the required heat sealability, it is suitable for use in overlapping packaging. A heat-shrinkable polylactic acid-based film can be provided.

[0042]

EXAMPLES Next, the present invention will be specifically described based on Examples. In addition, in the following Examples and Comparative Examples, each evaluation item was evaluated as follows. (1) A heat-sealable film was cut into a strip shape having a length of 15 mm × 100 mm in the MD direction, two strip-shaped samples were superposed, and set so as to be orthogonal to a heat sealer having a heat seal bar of 20 mm width. Then, it was heated from one side at a predetermined temperature and heat-sealed at a pressure of 0.2 MPa for 2 seconds. At this time, the heat seal layers were set so that they were on the inner side. The sample was subjected to a T-type peeling test using an autograph manufactured by Shimadzu Corporation according to JIS K-6854 until peeling was performed at a peeling speed of 300 mm / min, or until an adhesive portion remained 1 mm. . Then, the peak value at that time was taken as the heat seal strength and evaluated according to the following criteria. ×: Less than 5 N / cm (poor) Δ: 5 N / cm or more and less than 7 N / cm (somewhat inferior) ○: 7 N / cm or more and less than 10 N / cm (good) ◎: 10 N / cm or more (excellent)

(2) Heat Shrinkage A film sample cut into a length of 10 mm × 150 mm was heat-treated at 100 ° C. for 5 minutes in a hot air dryer. The sample length before heat treatment was set to 100%, and the heat shrinkage ratio was calculated from the difference between the sample length before and after heat treatment by the following equation. Thermal shrinkage (%) = [(length before heat treatment-length after heat treatment) /
Length before heat treatment] × 100 (3) Melting point and heat of crystal fusion Using a DSC manufactured by Perkin Elmer, the sample was dried and then weighed 7 mg. The sample was heated at a temperature rising rate of 20 ° C./min to obtain the melting point and its value. The heat of fusion of crystal was measured.

(4) Shrinkable magnetic cassette tape cases were subjected to heat shrinking (shrinking) at 130 ° C. for packaging, and then the appearance of the film was observed and evaluated according to the following criteria. . ◯: No wrinkle is generated, or there is a tight feeling and it looks good. Δ: Wrinkles are noticeable in the seal portion, or looseness due to insufficient heat shrinkage is observed. X: Marked wrinkles or markedly bulging appearance. (5) Printability On the surface-treated surface of the biaxially stretched film, two-color printing of red and white was performed with a gravure coater using a two-component urethane ink manufactured by Dainippon Ink and Chemicals. Then, from the printing deviation at that time, the evaluation was made according to the following criteria. ○: No print misalignment △: Some print misalignment ×: Significant print misalignment

(Production of Test Film) Film A Polylactic acid (manufactured by Cargill Dow Polymer Co., Ltd .: D-form 4%,
Melting point 151 ° C., heat of crystal fusion 29.9 J / g),
It was melt extruded from a T-die at 230 ° C., and was closely adhered to a cast roll at 25 ° C. to be rapidly cooled to obtain a 240 μm-thick unstretched sheet. The unstretched sheet obtained is preheated to 60
After preheating at ℃, it was stretched in the machine direction by 3 times at a draw roll temperature of 75 ℃, and then in the tenter at 80 ℃, it was stretched in the transverse direction 4 times.
It was stretched twice. Then, the relaxation rate in the transverse direction was set to 4%, and heat treatment was performed at 125 ° C. to obtain a biaxially stretched film A having a thickness of 20 μm.

Film B Polylactic acid (manufactured by Cargill Dow Polymer Co .: D body 1%,
Melting point 166 ° C., heat of crystal fusion 39.5 J / g),
It was melt extruded from a T-die at 230 ° C., and was closely adhered to a cast roll at 25 ° C. and rapidly cooled to obtain an unstretched sheet having a thickness of 180 μm. The obtained unstretched sheet was simultaneously biaxially stretched in a tenter at 80 ° C. three times in the machine direction and three times in the transverse direction, and then 125
Heat treated at ℃, 20μm thick biaxially stretched film B
Got

Films C and D Using the same polylactic acid as Film A, under the conditions shown in Table 1,
Biaxially stretched films C and D were obtained in the same manner as the film A.

Film E Biaxially stretched film E was obtained in the same manner as in film B except that the same polylactic acid as film B was used and the stretching conditions and heat treatment temperatures shown in Table 1 were used.

Film G Aliphatic-Aromatic Copolyester (E manufactured by BASF: E
coflex F, melting point 105 ° C., heat of crystal fusion 19.
5 J / g), melted at 180 ° C., extruded from an inflation film-forming machine with a die diameter of 100 mm,
With a take-up speed of 20 m / min, a folding diameter of 350 mm,
A film G having a thickness of 20 μm was obtained.

Film H Aliphatic polyester (Showa High Polymer: Bionole # 30
01, melting point 96 ° C., heat of fusion of crystal 45.6 J / g) and in the same manner as film G to obtain film H.

Film I Polyester carbonate (manufactured by Mitsubishi Gas Chemical Co., Inc .: IUP
EC550, melting point 97 ° C, heat of crystal fusion 47.9J /
g), melt-extruded at 210 ° C from a T-die,
The film was adhered to the cast roll of No. 3 and rapidly cooled to obtain a film I having a thickness of 20 μm.

Film J Polylactic acid (manufactured by Cargill Dow Polymer Co .: D body 4%,
Melting point 151 ° C., heat of fusion of crystals 29.9 J / g) 70% by mass and aliphatic-aromatic copolyester (Eastma)
n Chemical Company: EAST
ER BIOGP Copolyester, melting point 10
A film J was obtained in the same manner as the film I using 8 ° C. and a heat of crystal fusion of 18.5 J / g) of 30 mass%.

Film K Polylactic acid (manufactured by Cargill Dow Polymer Co .: D body 8%,
A film K was obtained in the same manner as the film I using a melting point of 130 ° C. and a heat of crystal fusion of 5.0 J / g).

Film L Polylactic acid (manufactured by Cargill Dow Polymer Co .: D body 1%,
Melting point 166 ° C., heat of crystal fusion 39.5 J / g),
A film L was obtained in the same manner as the film I.

The biaxially stretched film was obtained in the same manner as in the case of the film A except that the same polylactic acid as the films M and N film A was used and the stretching conditions and heat treatment temperatures shown in Table 1 were used.

(Examples and Comparative Examples) Example 1 Polylactic acid (C-Gill Dow Polymer Co., Ltd .: D-form = 1%) was used as the base material layer, and polylactic acid (Cargill Dow Polymer Co., Ltd.) was used as the heat-sealing layer. Made: D body = 4%) 80
Mass% and aliphatic-aromatic copolyester (BASF
(Manufactured by: Ecoflex F) A blend with 20% by mass was used. Then, these were melted at 230 ° C. and coextruded to obtain an unstretched film having a thickness of 300 μm (base material layer: 150 μm, heat seal layer: 150 μm). This unstretched film was stretched at 70 ° C. in the machine direction at a draw ratio of 2.5 times, then at 80 ° C. in the transverse direction at a draw ratio of 3 times, and then heat-treated at 130 ° C. to obtain a biaxial film of 40 μm. A stretched laminated film was obtained.

Examples 2 to 6, Comparative Examples 1 to 4 Films A to E, M and N were used as the base material layer, and the base material layer was
Apply an aliphatic polyester adhesive with a thickness of 1 μm,
After drying at 80 ° C., the films G to L as heat-sealing layers were pressure-bonded with a heating roll at 90 ° C., and further aged at 40 ° C. for 3 days to obtain a laminated film. However, the heat seal layer was not formed only in Comparative Example 1.

Table 1 shows the details of Examples 1 to 6 and Comparative Examples 1 to 4.
Shown in.

[0059]

[Table 1]

As is clear from Table 1, Examples 1 to 1
Each of the films of 6 satisfied the conditions of the present invention, was formed of a biodegradable polymer, and had the required heat sealability, heat shrinkability, and shrinkability. It was also excellent in printability.

On the other hand, Comparative Example 1 was inferior in heat sealability because it did not have a heat seal layer. Comparative Example 2 satisfies the condition of the present invention that the melting point of polylactic acid forming the heat-sealing layer is equal to the melting point of polylactic acid forming the base material layer and lower than the melting point of polylactic acid forming the base material layer. Therefore, the heat sealability was poor.

In Comparative Example 3, the thermal shrinkage was too high in both the MD and TD directions, so the shrink properties were poor and the printability was also poor. Comparative Example 4 was inferior in shrink properties because the thermal shrinkage in the MD direction was too low.

[0063]

As described above, according to the present invention, a base material layer formed of a polylactic acid-based film and a biodegradable polymer having a lower melting point or softening point than the polylactic acid forming the base material layer are contained. And a heat seal layer formed as the outermost layer by the film
Heat shrinkage in MD is 5-10% and in TD is 5%
% So that it has an appropriate heat shrinkability,
Moreover, since the heat-sealing layer has a required heat-sealing property, it is possible to provide a heat-shrinkable polylactic acid-based film suitable for use in overlapping packaging.

Continued front page    F term (reference) 4F100 AK01B AK41A AK41J AK45B                       AK45J AL01B AL05B EH20                       EJ38 GB15 JA03A JA04B                       JC00A JC00B JL12B YY00B                 4J002 CF03X CF18W CF19W CG04X                       GG02

Claims (6)

[Claims] 1. A heat-shrinkable polylactic acid-based film having a laminated structure, which has a lower melting point or softening point than a base material layer formed of the polylactic acid-based film and polylactic acid forming the base material layer. And a heat-sealing layer formed as the outermost layer by a film containing a degradable polymer, and having a heat shrinkage ratio at 100 ° C. of 5 to 10 in the MD direction.
% And 5% or less in the TD direction, a heat-shrinkable polylactic acid-based film. 2. The heat seal layer is formed of a film containing at least one of an aliphatic polyester, an aliphatic-aromatic copolyester, and a polyester carbonate. The heat-shrinkable polylactic acid-based film described. 3. The film forming the heat seal layer comprises:
A blend of the same polylactic acid that forms the base material layer and a biodegradable polymer having a lower melting point or softening point than this polylactic acid, or a biodegradable polymer simple substance having a lower melting point or softening point than the polylactic acid. It is formed by either of them, and the blend ratio is (polylactic acid) / mass ratio.
(Biodegradable polymer) = 90/10 to 0/100, The heat-shrinkable polylactic acid-based film according to claim 2. 4. The melting point or softening point of the biodegradable polymer forming the heat-sealing layer is 10 ° C. or more lower than the melting point or softening point of polylactic acid forming the base material layer. The heat-shrinkable polylactic acid-based film according to any one of 3 to 3. 5. The heat-sealing strength when the heat-sealing layers of the film are laminated and bonded to each other is 7N.
/ Cm or more, the heat-shrinkable polylactic acid-based film according to any one of claims 1 to 4. 6. The heat shrinkage according to claim 1, wherein the biodegradable polymer having a melting point or softening point lower than that of polylactic acid has a heat of crystal fusion of 40 J / g or less. Polylactic acid based film.