JP6717657B2 - Biodegradable film - Google Patents

Description

TECHNICAL FIELD The present invention relates to a biodegradable film, and more particularly to a biodegradable film suitable for a biodegradable compost bag, an agricultural film, a packaging material and the like.

A film obtained by molding a biodegradable resin is expected to be used as a film for agricultural materials, civil engineering materials, planting materials, packaging materials and the like (see, for example, Patent Documents 1 and 2). However, these films have problems in practical use because they have insufficient tear strength and film impact strength.

Patent Document 3 discloses a composition containing an aliphatic aromatic polyester, an aliphatic polyester, and polylactic acid for the purpose of adjusting the biodegradability rate and improving the tear strength and impact resistance. However, regarding the proportion of polylactic acid, the upper limit is preferably 30% by mass or less from the viewpoint of film physical properties, and specifically, only data such as tear strength at 10% by mass is disclosed. That is, increasing the proportion of polylactic acid for the purpose of obtaining a high biodegradability rate and achieving good impact resistance are not compatible with each other.

Japanese Unexamined Patent Publication No. 5-271377 JP-A-6-170941 JP, 2014-156541, A Japanese Patent Publication No. 47-33279 U.S. Pat. No. 2,941,956

Journal of 0rorganic Chemistry 28, 2069-2075 (1963), Chemical Review 1981, Vol. 81, No. 4, p619-621

Therefore, an object of the present invention is to provide a biodegradable film having an improved film impact strength by using polylactic acid in a certain amount or more.

That is, the present invention includes the following inventions.

[1] A film of a blend resin of polylactic acid (A) and a polyester polymer (B) containing at least an aliphatic polyester copolymer (Ba) and an aliphatic aromatic polyester copolymer (Bb) And
In the observation of the phase image by the tapping mode AFM of the scanning probe microscope of the cross section of the film stretching direction (MD) and the thickness direction,
The image is composed of a discontinuous phase of polylactic acid (A) and a discontinuous phase of any one of the aliphatic polyester copolymer (Ba) and the aliphatic aromatic polyester copolymer (Bb),
Each discontinuous phase has a layered structure,
A film characterized in that the width of the discontinuous phase layer of the polylactic acid (A) in the thickness direction is 50 nm or less on average.
[2] The film according to the above item [1], wherein the aliphatic polyester copolymer (Ba) is a polymer of an aliphatic diol and an aliphatic dibasic acid.
[3] The aforementioned item [1] or [2], wherein the aliphatic aromatic polyester copolymer (Bb) is a polymer of an aliphatic diol, an aromatic dibasic acid and an aliphatic dibasic acid. Film.
[4] The film as described in [2] or [3] above, wherein the aliphatic diol is 1,4-butanediol.
[5] The film according to any one of items [2] to [4], wherein the aliphatic dibasic acid is succinic acid or adipic acid.
[6] The film according to any one of items [2] to [5], wherein the aliphatic polyester copolymer (Ba) further contains a polymer of butanediol and succinic acid.
[7] The film according to any one of [1] to [6] above, wherein the polylactic acid (A) is contained in the film in an amount of 31 to 50% by mass or less.
[8] The film according to any one of items [1] to [7], further including a carbodiimide compound (C).
[9] The film according to any one of [1] to [9] above, further including a lubricant (D).

According to the present invention, a biodegradable film having improved film impact strength is provided even when a certain amount or more of polylactic acid is used.

It is an example of a scanning probe microscope image (field of view: 2.5 μm square) of a cross section in the stretching direction and the thickness direction of the film of the present invention.

The film of the present invention is a blend of polylactic acid (A) and a polyester polymer (B) containing at least an aliphatic polyester copolymer (Ba) and an aliphatic aromatic polyester copolymer (Bb). When observing a phase image of a resin film in a cross section in the stretching direction (MD) and the thickness direction of the film by a tapping mode AFM of a scanning probe microscope, the image shows a discontinuous phase of polylactic acid (A). It comprises a discontinuous phase of either the aliphatic polyester copolymer (Ba) or the aliphatic aromatic polyester copolymer (Bb), and each discontinuous phase has a structure dispersed in a layered form. The width of the discontinuous phase layer of the polylactic acid (A) in the thickness direction is observed to be 50 nm or less on average. Furthermore, the film of the present invention preferably contains a carbodiimide compound (C) and/or a lubricant (D).

<Polylactic acid (A)> The polylactic acid (A) may be a polymer of a lactic acid monomer. For example, poly L-lactic acid whose structural unit is L-lactic acid, poly D-lactic acid whose structural unit is D-lactic acid, poly DL-lactic acid whose structural unit is L-lactic acid and D-lactic acid, and mixtures thereof. Polymers containing as a main component (50 mol% or more) are listed.

Further, the above-mentioned polylactic acid preferably has a molar ratio of D-lactic acid:L-lactic acid=100:0 to 85:15 or 0:100 to 15:85. It is also possible to blend other polylactic acid having different composition ratios of D-lactic acid and L-lactic acid.

Furthermore, the polylactic acid (A) may be a copolymer of the above-mentioned lactic acid and another hydroxycarboxylic acid unit described below, and may contain a small amount of a chain extender residue. Other hydroxycarboxylic acid units include optical isomers of lactic acid (D-lactic acid for L-lactic acid, L-lactic acid for D-lactic acid), glycolic acid, 3-hydroxybutyric acid, 4-hydroxybutyric acid. , 2-hydroxy-n-butyric acid, 2-hydroxy-3,3-dimethylbutyric acid, 2-hydroxy-3-methylbutyric acid, 2-methyllactic acid, 2-hydroxycaproic acid and other bifunctional aliphatic hydroxycarboxylic acids, and Lactones such as caprolactone, butyrolactone, valerolactone and the like can be mentioned. These may be used alone or in combination of two or more. Such other hydroxycarboxylic acid unit is preferably used in less than 15 mol% in the component (A).

The polylactic acid (A) used in the present invention preferably has a weight average molecular weight of 60,000 to 700,000, more preferably 80,000 to 400,000, and particularly preferably 100,000 to 300,000. When the molecular weight is 60,000 or more, practical physical properties such as mechanical properties and heat resistance are good, and when it is 700,000 or less, melt viscosity is low and molding processability is excellent.

The content of the polylactic acid (A) in the film of the present invention is preferably 31 to 50% by mass, more preferably 31 to 48% by mass, and further preferably 31 to 46% by mass. By setting the polylactic acid (A) within the above range, the film of the present invention can be a film having an appropriate biodegradation rate and hydrolysis rate.

<Polyester Polymer (B)> The polyester polymer (B) is a polyester polymer other than the polylactic acid (A), and includes an aliphatic polyester copolymer (Ba) and an aliphatic aromatic polyester polymer. (Bb) is included. The mixture of the aliphatic polyester copolymer (Ba) and the aliphatic aromatic polyester polymer (Bb) provides a good balance between the heat seal strength and the film impact strength of the film molded product.

The aliphatic polyester copolymer (Ba) is preferably a polymer of an aliphatic diol and an aliphatic dibasic acid, and further preferably contains a copolymer of butanediol and succinic acid. ..

The aliphatic aromatic polyester polymer (Bb) is preferably a polymer of an aliphatic diol, an aromatic dibasic acid and an aliphatic dibasic acid.

The polyester polymer (B) has a melting point of preferably 50 to 190° C., more preferably 60 to 150° C., and a weight average molecular weight of preferably 50,000 or more, more preferably 1 million or more. is there. Within these ranges, it is easy to obtain a molded product such as a film having high film impact strength.

<Carbodiimide compound (C)>
The film of the present invention preferably contains a carbodiimide compound (C). The carbodiimide compound (C) preferably has an isocyanato group at both ends. These are known methods, for example, by using an organic phosphorus compound or an organometallic compound as a catalyst, various polyisocyanate compounds in the presence or absence of an inert solvent at a temperature of about 70° C. or higher at a decarboxylation condensation reaction. It can be synthesized by

Examples of the monocarbodiimide compound, which is an example of the carbodiimide compound (C), include dimethylcarbodiimide, diisopropylcarbodiimide, diisobutylcarbodiimide, dioctylcarbodiimide, t-butylisopropylcarbodiimide, diphenylcarbodiimide, di-t-butylcarbodiimide, di-β-. Examples thereof include naphthylcarbodiimide and dicyclohexylcarbodiimide. Among these, diisopropylcarbodiimide or dicyclohexylcarbodiimide is preferable from the viewpoint of being easily produced on an industrial scale and easily available.

Polycarbodiimide, which is an example of the carbodiimide compound (C), can be produced by various methods, for example, the methods described in Patent Documents 3 to 5 and Non-Patent Document 1 and the like.

<Lubricant (D)>
The film of the present invention preferably contains a lubricant (D) (also referred to as “slip agent”) in order to prevent blocking between the films and maintain openness after production. Examples of the lubricant (D) include, if desired, lubricants usually used in the technical field, and these can be added within a range not impairing the characteristics of the present invention.

Examples of the lubricant (D) include fatty acid monoamide and fatty acid bisamide. Examples of the fatty acid monoamide include caproic acid amide, caprylic acid amide, capric acid amide, lauric acid amide, myristic acid amide, palmitic acid amide, stearic acid amide, arachidic acid amide, behenic acid amide, palmitoleic acid amide, and oleic acid amide. , Eicosenoic acid amide, erucic acid amide, elaidic acid amide, trans 11 eicosenoic acid amide, trans 13 docosenoic acid amide, linoleic acid amide, linolenic acid amide, ricinoleic acid amide, and erucic acid amide. Examples of the fatty acid bisamide include methylenebisstearic acid amide, ethylenebisstearic acid amide, ethylenebislauric acid amide, ethylenebiscapric acid amide, ethylenebishydroxystearic acid amide, ethylenebisbehenic acid amide, and hexamethylenebisstearic acid amide. , Hexamethylenebisbehenic acid amide, hexamethylenebishydroxystearic acid amide, N,N'-distearyl adipic acid amide, N,N'-distearyl sebacic acid amide, ethylenebisoleic acid amide, ethylenebiserucic acid amide, Hexamethylenebisoleic acid amide, N,N'-dioleyl adipate amide, N,N'-dioleyl sebacic acid amide and the like can be mentioned.
Specific examples include, for example, "Alflo" (Nippon Yushi), "Diamid" (Nippon Kasei), "Fatty Acid Amide" (Kao) and the like.

Furthermore, the film of the present invention may contain, as other additives, for example, an antioxidant, a heat stabilizer, an anti-UV agent, an antistatic agent, a flame retardant, a crystallization accelerator and the like.

<Structure of Film of the Present Invention> In the observation of a phase image by a tapping mode AFM of SPM of a cross section in the stretching direction (MD) and the thickness direction of the film of the present invention (field of view: 2.5 μm square), the image is polylactic acid. The discontinuous phase of (A) and the discontinuous phase of any one of the aliphatic polyester copolymer (Ba) and the aliphatic aromatic polyester copolymer (Bb), each of the discontinuous phases. It has a layered structure, and the width of the discontinuous phase layer of the polylactic acid (A) in the thickness direction is 50 nm or less on average, preferably 20 to 50 nm, and more preferably 40 to 50 nm. .. If it cannot be confirmed in the same visual field whether or not it is the discontinuous phase, it can be confirmed by sequentially observing adjacent regions.

Regarding the sample preparation for cross-section observation, it is preferable that it is prepared by a physical method or a method using an ion beam after the film embedding process, because it is easy to observe. Furthermore, it is more preferable to carry out by the method of Examples described later.

<The manufacturing method of the film of this invention> As a manufacturing method of the film of this invention, first, polylactic acid (A), and at least an aliphatic polyester copolymer (Ba) and an aliphatic aromatic polyester copolymer ( B-b) and a polyester polymer (B) may be kneaded to produce a resin composition, which may be molded into a film, or the polylactic acid (A) and the polyester polymer (B) may be mixed together. It may be directly charged into the molding machine.

The method for producing the resin composition is not particularly limited, and the polylactic acid (A) and the polyester polymer (B) are commonly used in kneaders, roll mills, Banbury mixers, single-screw or twin-screw extruders, etc. Melt kneading using the kneading machine described above to obtain a composition pellet. Alternatively, a carbodiimide compound (C) and an additive (D) may be mixed in a specific resin in advance to prepare a masterbatch, which may then be kneaded with an extruder or a molding machine.

The film may be formed by a commonly used known forming method. Examples thereof include a water-cooled or air-cooled inflation molding method, a T-die type film extrusion molding method, and an extrusion lamination molding method. Further, the film of the present invention may be a film obtained by further uniaxially or biaxially stretching the film.

The temperature at the time of molding is important in order to develop the physical properties and form the morphology, and molding at 210° C. or lower is preferable. More preferably, it is 200°C, most preferably 190°C. If it exceeds 210°C, the morphology changes, and the physical properties of the film, especially the film impact strength, deteriorate. Here, the molding temperature is a set temperature of the extruder and the die.

Hereinafter, the present invention will be described in more detail with reference to Examples, but the present invention is not limited thereto. [Measurement and Evaluation Method] The measurement and evaluation shown in the examples were carried out under the following conditions. (1) Dispersion structure film is placed on a jig, embedded with UV curable resin, and then trimmed with a razor to remove the excess resin portion, and the cross section is observed with the stretching direction of the film as the vertical direction and the thickness direction as the horizontal direction. Was exposed, and platinum was vapor-deposited for the purpose of making it easier to find an observation target site during SPM measurement. When the film is biaxially stretched, the stretching direction is the machine direction (MD direction) of the molding machine.

The cross section of the film sample was cut using an ultramicrotome to prepare a smooth surface. Since the Tg of the film is lower than room temperature, a cryo unit was used and the device temperature was set to −100° C. to cool the sample to Tg or lower and perform cutting. A glass knife was used as the knife, the cutting thickness was 80 to 300 nm, and the cutting speed was 0.3 mm/s.

The cross section of the film was observed near the center of the film using a tapping mode AFM of a scanning probe microscope (SPM) (Agilent 5500 manufactured by Agilent). The scan range was 2.5 μm square, the scan speed was 0.5 line/s, the data density was 256×256, and the probe was NCH manufactured by NanoWorld.

The observed image is such that the stretching direction of the film is vertical, the thickness direction is horizontal, and ten straight lines are drawn at equal intervals in the horizontal direction, and the boundary between the straight line and the phase dispersed in layers that is long in the length direction of the film. Based on the intersection point with, the phase structures at the left and right ends were omitted, and the width of the polylactic acid phase was measured at 10 positions from the left end side of the straight line, a total of 100 positions, and the average value was calculated.

The method for identifying the polylactic acid (A) phase, the aliphatic polyester copolymer (Ba) phase, and the aliphatic aromatic polyester copolymer (Bb) phase in the observed image is shown below. The phase image of SPM reflects the difference in the physical properties of the sample surface. The phase delay of the cantilever drive signal and the response vibration signal is detected, and the hard area with a relatively small phase delay has a bright color range and a phase. A soft region with a large delay is represented as a dark color region. Therefore, the surface hardness of each component contained in the sample serves as an index for identifying each domain in the phase image.

The surface hardness of the raw material simple substance film was measured by polylactic acid (A), and a polyester polymer (B) aliphatic polyester copolymer (B-a) simple substance film and an aliphatic aromatic polyester copolymer (B-b). ) After press-molding the single film, the film was left to stand in a constant temperature and constant humidity chamber (23°C/50%) overnight, and the durometer hardness meter (HD-1120 (TypeD)/made by Ueshima) was used. The polylactic acid (A) is the region most represented as the bright color region in the phase image, the aliphatic aromatic polyester copolymer (Bb) is the region most represented as the dark color region, and the aliphatic polyester It was judged that the copolymer (Ba) was the region represented by the brightness between them. For example, in FIG. 1, it is determined that the polylactic acid (A) phase is 1, the aliphatic polyester copolymer (Ba) phase is 2, and the aliphatic aromatic polyester copolymer (Bb) phase is 3. ..

(2) Film Impact Strength (kJ/m) According to JIS P 8134, strength was measured by a paperboard-impact open strength test method.

(3) Raw materials The following raw materials were used. [(A) Polylactic acid] Inge2003D manufactured by NatureWorks [Polyester polymer (B)] (Ba-1) Aliphatic polyester copolymer Showa Denko KK Bionole 5001MD (Bb-1) Aliphatic fragrance Group polyester copolymer BASF Corporation dehydration condensation type aliphatic aromatic polyester Ecoflex (Ba-2) polymer of butanediol and succinic acid Showa Denko KK Bionole 1020MD [(C) carbodiimide compound] Nisshinbo Co., Ltd. Carbodilite HMC-15CA [(D) lubricant] Kao Corporation fatty acid amide E (erucic acid amide)

[Film Forming] All the resins and additives were mixed in a tumbler for 30 minutes, and then melt-kneaded at 190° C. using a twin-screw extruder in the same direction with a screw diameter of 30 mm to obtain composition pellets. The obtained pellets of Example were dried at a temperature of 80° C. for 3 hours with a dehumidified air circulation dryer, and then a film was formed with an inflation molding machine.

From the results shown in Table 1, the film of the example in which the width in the thickness direction of the discontinuous phase of polylactic acid (A) is 50 nm or less on average has a higher film impact strength than the film of the comparative example wider than 50 nm. It turns out that is excellent.

INDUSTRIAL APPLICABILITY The biodegradable film of the present invention has high film impact strength and is suitably used as a compost bag, an agricultural film, a packaging material and the like.

Claims (7)

A film of a blend resin of polylactic acid (A) and a polyester polymer (B) containing at least an aliphatic polyester copolymer (Ba) and an aliphatic aromatic polyester copolymer (Bb), ,
The film further comprises a carbodiimide compound (C),
The polylactic acid (A) is contained in the film in an amount of 31 to 50% by mass,
In the observation of the phase image by the tapping mode AFM of the scanning probe microscope of the cross section of the film stretching direction (MD) and the thickness direction,
The image is composed of a discontinuous phase of polylactic acid (A) and a discontinuous phase of any one of the aliphatic polyester copolymer (Ba) and the aliphatic aromatic polyester copolymer (Bb),
Each discontinuous phase has a layered structure,
A film characterized in that the width of the discontinuous phase layer of the polylactic acid (A) in the thickness direction is 50 nm or less on average. The film according to claim 1, wherein the aliphatic polyester copolymer (Ba) is a polymer of an aliphatic diol and an aliphatic dibasic acid. The film according to claim 1 or 2, wherein the aliphatic aromatic polyester copolymer (Bb) is a polymer of an aliphatic diol, an aromatic dibasic acid and an aliphatic dibasic acid. The film according to claim 2, wherein the aliphatic diol is 1,4-butanediol. The film according to claim 2, wherein the aliphatic dibasic acid is succinic acid or adipic acid. Further, the film according to claim 2, wherein the aliphatic polyester copolymer (Ba) contains a polymer of butanediol and succinic acid. Further, the film is a film according to any one of claims 1 to 7 including the lubricant (D).