Biodegradable resin film

Abstract

To provide a biodegradable resin film which, when stretched while being unwound from a roll, can be improved in tear strength in a longitudinal direction (MD direction) of the film, that is, tearing of which can be suppressed in the longitudinal direction while not using a plasticizer, and which, while comprising polylactic acid, can be improved in storability due to suppressed hydrolysis.SOLUTION: A biodegradable resin film does not contain a plasticizer but comprises a biodegradable resin and an additive, wherein the biodegradable resin comprises an aliphatic aromatic polyester-based resin and a polylactic acid-based resin, 5 to 30 mass% of the polylactic acid-based resin and 40 to 92 mass% of the aliphatic aromatic polyester-based resin are contained with respect to 100 pts.mass of the biodegradable resin film, and the carboxylic acid value of the biodegradable resin film calculated by the following expression (1) is 25 mmol / kg or less, and the biodegradable resin film is suitable as an agricultural multi-film and a single layer film or a multilayer film.SELECTED DRAWING: None

Description

[Technical field]

[0001] The present invention relates to a biodegradable resin film that can improve tear strength and can also suppress hydrolysis to improve storage properties. [Background technology]

[0002] It is known that biodegradable resin films are inferior in flexibility and film strength and are difficult to mold compared to general films such as polyethylene (PE) and polyvinyl chloride (PVC). Therefore, flexibility and moldability are controlled by mixing multiple biodegradable resins or using additives such as plasticizers. For example, it is known that film strength and flexibility can be adjusted by mixing a polylactic acid resin with a biodegradable resin such as an aliphatic aromatic polyester resin or an aliphatic polyester resin, and a biodegradable resin film is known that is a mixture of a polylactic acid resin, an aliphatic aromatic polyester resin (e.g., PBAT) and a plasticizer (Patent Document 1).

[0003] However, when a plasticizer is added, the plasticizer seeps out onto the film surface over time, which is known as bleeding out. For example, when a biodegradable resin film containing a plasticizer is used as an agricultural mulch film, if the film surface becomes sticky due to bleeding out of the plasticizer, it becomes difficult to unwind the film from the roll, making it difficult to unroll the film and impairing workability.

[0004] Patent Document 2 also discloses that a biodegradable film having excellent formability and impact strength can be obtained by mixing aliphatic aromatic polyester resins and aliphatic polyester resins and the type of dicarboxylic acid constituting these resins without requiring polylactic acid resins or plasticizers. However, biodegradable resin films made by mixing aliphatic aromatic polyester resins and aliphatic polyester resins are insufficient in terms of tear strength in the longitudinal direction (MD direction) of the film, which is required when spreading the film with a machine such as a mulcher for agricultural mulch films. The tear strength in the longitudinal direction (MD direction) of a film is a numerical value that indicates how easily the film tears when a cut is made in the longitudinal direction of the film and the film is torn parallel to the cut, and the higher the tear strength, the less likely the film is to tear in the longitudinal direction.

[0005] On the other hand, even if the strength of the film can be improved by mixing a polylactic acid resin with a biodegradable resin such as an aliphatic aromatic polyester resin or an aliphatic polyester resin, polylactic acid is known to be a hydrolyzable resin. Therefore, if a film containing polylactic acid is left at room temperature for a long period of time in a warehouse, for example, hydrolysis will progress. As a result, the film cannot be stored for a long period of time in a rolled state after film formation, and improvements in storage properties are required. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] JP 2009-138085 A [Patent Document 2] Patent Publication No. WO2014 / 064983 Summary of the Invention [Problem to be solved by the invention]

[0007] Therefore, the present invention aims to provide a biodegradable resin film that does not use a plasticizer, but can suppress tear strength in the longitudinal direction (MD direction) of the film, i.e., tearing in the longitudinal direction, when it is unwound from a roll and spread out as an agricultural mulch film, and further suppresses hydrolysis to improve storage properties. [Means for solving the problem]

[0008] As a result of intensive research conducted by the inventors in order to achieve the above-mentioned object, they discovered that the biodegradable resin film of the present invention has improved tear strength, suppresses hydrolysis, and improves storage properties, and is suitable as an agricultural mulch film, which led to the completion of the present invention.

[0009] That is, in a first aspect, the present invention relates to a biodegradable resin film that does not contain a plasticizer and contains a biodegradable resin and an additive, wherein the biodegradable resin contains an aliphatic aromatic polyester resin and a polylactic acid resin, and the biodegradable resin contains 5 to 30 mass% of the polylactic acid resin and 40 to 92 mass% of the aliphatic aromatic polyester resin relative to 100 mass% of the biodegradable resin film, and the carboxylic acid value of the biodegradable resin film calculated by the following formula (1) is 25 mmol / kg or less, and the biodegradable resin film is suitable as an agricultural mulch film.

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[0010] First, the biodegradable resin film of the present invention does not bleed out due to the plasticizer, and the exudation of components from the film surface is suppressed. In addition, by specifying the blending ratio of the polylactic acid resin and the aliphatic aromatic polyester resin, and the carboxylic acid value of the film, the biodegradable resin film of the present invention has improved tear strength compared to previous biodegradable resin films, and is less likely to tear when stretched, and hydrolysis is suppressed, which has the effect of improving storage properties. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0011] <Biodegradable resin film> The biodegradable resin film of the present invention contains a biodegradable resin and an additive, but does not contain a plasticizer to prevent bleed-out. The biodegradable resin film of the present invention may be a single-layer film or a multilayer film having a multilayer laminate structure.

[0012] (biodegradable resin) A biodegradable resin is a resin that has the same functions as conventional petroleum-derived plastics when in use, and is biodegraded by microorganisms in the soil or water of the natural world over a certain period of time after use, and is ultimately hydrolyzed into water and carbon dioxide. The biodegradable resin used in the present invention includes polylactic acid-based resins and aliphatic aromatic polyester-based resins.

[0013] (Biodegradable resin - polylactic acid resin) The polylactic acid resin of the present invention is not particularly limited as long as it is a condensation product of lactic acid (polylactic acid (PLA)), and may be a poly-L-lactic acid resin or a poly-D-lactic acid resin. It may also be a mixture thereof (for example, a stereocomplex type polylactic acid resin in which a poly-L-lactic acid resin and a poly-D-lactic acid resin are mixed).

[0014] (Biodegradable resin - Aliphatic aromatic polyester resin) Examples of the aliphatic aromatic polyester resin of the present invention include polybutylene adipate terephthalate resin, polybutylene terephthalate alkylate resin, and polybutylene succinate terephthalate resin. In particular, polybutylene adipate terephthalate (PBAT) is preferred. Polybutylene adipate terephthalate (PBAT) is produced by polycondensation reaction of a dicarboxylic acid component consisting of adipic acid and terephthalic acid with a diol component consisting of 1,4-butanediol, but other components can be included. For example, other diol components can be included. Examples of other diol components include 2,3-butanediol, 1,3-butanediol, 1,4-pentanediol, 2,4-pentanediol, 1,6-hexanediol, neopentyl glycol, ethylene glycol, and diethylene glycol.

[0015] (Biodegradable resins - Others) The biodegradable resin used in the present invention may further contain known biodegradable resins, etc., within the scope of the object of the invention. Examples of such resins include aliphatic polyester resins such as polybutylene succinate (PBS), polyethylene succinate (PES), polybutylene succinate adipate (PBSA), and polycaprolactone (PCL); polyhydroxyalkanoic acid (PHA) resins such as polyhydroxybutyric acid; and natural polymers such as starch and cellulose.

[0016] One object of the present invention is to improve the tear strength in the longitudinal direction (MD) of a biodegradable resin film. A biodegradable resin film containing a mixture of an aliphatic aromatic polyester resin and an aliphatic polyester resin is insufficient in tear strength in the longitudinal direction (MD) of the film required when spreading the film with a machine such as a mulcher for agricultural mulch film, and may tear when spread by the machine. Therefore, by adding a polylactic acid resin, the tear strength in the longitudinal direction (MD) of the film can be improved.

[0017] Therefore, the biodegradable resin film of the present invention contains 5 to 30% by mass of polylactic acid resin and 40 to 92% by mass of aliphatic aromatic polyester resin, based on 100% by mass. If the amount of polylactic acid resin added is less than 5% by mass, sufficient tear strength in the machine direction (MD) is not achieved, and if it is more than 30% by mass, tear strength decreases not only in the machine direction (MD) but also in the transverse direction (TD). The biodegradable resin with this constitution is suitable for improving tear strength. More preferably, the polylactic acid resin is contained in an amount of 13 to 26% by mass relative to 100% by mass of the biodegradable resin film.

[0018] On the other hand, polylactic acid resins have a tendency to easily undergo hydrolysis, which affects the storage stability of biodegradable resin films. In order to provide a biodegradable resin film that can improve tear strength, suppress hydrolysis, and improve storage stability, the present invention further adjusts the carboxylic acid value of the biodegradable resin film, as described below, thereby successfully suppressing hydrolysis of the film.

[0019] (Additives) The additives used in the present invention do not include plasticizers that cause bleed-out problems, and may include at least a fatty acid monoamide as an additive. Examples of the fatty acid monoamide include saturated fatty acid amides such as lauric acid amide, palmitic acid amide, stearic acid amide, behenic acid amide, and hydroxystearic acid amide, and unsaturated fatty acid amides such as oleic acid amide, erucic acid amide, and ricinoleic acid amide. Examples include:

[0020] As the fatty acid monoamide, it is preferable to use a saturated fatty acid amide in terms of bleeding and slip properties, and among them, stearic acid amide can be preferably used in terms of cost and performance.

[0021] The amount of the fatty acid monoamide added is preferably 0.3 to 1.2% by mass, and more preferably 0.6 to 1.0% by mass, relative to 100% by mass of the biodegradable resin film. When the amount of the fatty acid monoamide is 0.3% by mass or more, the contact angle of water with the film can be adjusted to 100° or more, and stable moisture permeability can be imparted. On the other hand, when the upper limit is set to 1.2% by mass, the environmental load can be reduced, making it suitable as a green plastic, and at the same time, problems such as bleeding and winding slippage are less likely to occur, which is preferable.

[0022] The biodegradable resin film of the present invention has a moisture permeability of 500 g / m2, calculated from the amount of moisture absorbed by the moisture absorbent when placed in a thermo-hygrostat at a temperature of 40° C. and a relative humidity of 90% for 72 hours, with reference to JIS Z 0208. 2 - 24h or less is preferable, and 400g / m 2 By setting the moisture permeability in the above range, the moisture retention of the soil can be better maintained. Therefore, the biodegradable resin film of the present invention is suitable as an agricultural mulch film.

[0023] In addition, other additives may be added to the composition constituting the biodegradable resin film of the present invention, if necessary, to the extent that the effects of the present invention are not impaired. For example, light stabilizers, heat stabilizers, lubricants, ultraviolet absorbers, photodecomposition promoters, biodegradation promoters, biodegradation inhibitors, fillers, pigments, etc. may be included.

[0024] <Carboxylic acid value of film> The carboxylic acid value is a value determined by the carboxyl group, and the smaller the carboxylic acid value, the better the hydrolysis resistance. The carboxyl group is thought to act as an acid catalyst and has the effect of promoting the hydrolysis of polyester resins.

[0025] In the present invention, the aliphatic aromatic polyester resin is not easily hydrolyzed, but since it has a carboxyl group at the end, it acts as an acid catalyst. This causes the polylactic acid resin to hydrolyze. In other words, if the carboxylic acid value of the film is large, it is thought that the hydrolysis of the polylactic acid resin in the film is promoted.

[0026] The carboxylic acid value of the biodegradable resin film of the present invention can be adjusted mainly by the carboxylic acid value of the aliphatic aromatic polyester resin, which is the main component, and the amount added.

[0027]

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[0028] The specific meanings of the sample titer, blank titer and sample collection amount in formula (1) will be referred to in the Examples below. When calculated using formula (1), it was found that if the carboxylic acid value of the film is higher than 25 mmol / kg, hydrolysis is likely to proceed and the storage period of the film is significantly shortened, and the biodegradable resin film of the present invention has a carboxylic acid value of 25 mmol / kg or less.

[0029] <Tear strength> When agricultural mulch films are spread, if the tear strength of the biodegradable resin film in the longitudinal direction (MD) is insufficient, the film often tears in the longitudinal direction when it is unwound from the roll. The biodegradable resin film of the present invention has a tear strength in the longitudinal direction (MD) of 100 N / cm or more (measured by the JIS K 6732 method (Elmendorf method)), which is effective in preventing tearing when the film is unwound from the roll and spread. Furthermore, it is more preferable that the tear strength in the longitudinal direction (MD) is 200 N / cm or more.

[0030] In addition, when the biodegradable resin film is unwound from the roll, if the tear strength in the transverse direction (TD) is insufficient, the film will tend to tear in the transverse direction, so tearing in the transverse direction must also be suppressed. Basically, like the longitudinal direction (MD), the tear strength in the transverse direction (TD) must be 100 N / cm or more, and more preferably 200 N / cm or more.

[0031] Here, the longitudinal direction of the film is the length (flow) direction during film formation, and the transverse direction is the width direction during film formation. In the present invention, the tear strength value is defined as the value (N / cm) obtained by dividing the tear strength (mN) measured based on JIS K 6732 (Elmendorf method) by the film thickness.

[0032] Furthermore, if the film has a good balance of tear strength in the machine direction (MD) and the cross direction (TD), the tearing portion is less likely to propagate, making it ideal for agricultural mulch films. The difference in tear strength between the machine direction (MD) and the transverse direction (TD) of the biodegradable resin film of the present invention is preferably 600 N / cm or less, more preferably 200 N / cm or less.

[0033] <Storability> The biodegradable resin film of the present invention is inhibited from hydrolyzing over time, which can be specifically evaluated by an accelerated test.

[0034] In this accelerated test, the film is left standing for one week under humid heat conditions (temperature 70°C, relative humidity 95%), which is equivalent to accelerating the test for one year. As hydrolysis progresses, the film becomes brittle and the elongation at break decreases. The biodegradable resin film of the present invention has an elongation at break in the transverse direction (TD) of 100% or more in a tensile test (based on JIS K 7127, tensile speed 200 mm / min), and hydrolysis over time is suppressed.

[0035] <Thickness> The thickness of the biodegradable resin film of the present invention is preferably 5 to 100 μm. If it is less than 5 μm, the strength of the film is insufficient and it may be easily torn, particularly when used for agricultural purposes, such as mulch film. On the other hand, if it exceeds 100 μm, the weight of the film may become heavy and it may take too long to biodegrade.

[0036] The biodegradable resin film of the present invention is a multilayer film having a multilayer laminated structure, and one embodiment of the film is a two-layer multilayer film having a white reflective layer and a black colored layer. A mulch film having such a reflective layer, a so-called black-and-white mulch film, has a white layer on the surface of a black film, and reflects solar radiation (radiation with a wavelength of 300 to 2500 nm) to suppress excessive rise in ground temperature in summer, while also providing the properties of a mulch film such as weed suppression.

[0037] In the present invention, the reflective layer contains, relative to 100% by mass of the reflective layer, 5 to 30% by mass of a polylactic acid resin, 40 to 92% by mass of an aliphatic aromatic polyester resin, and further contains titanium oxide. Includes.

[0038] In the present invention, the colored layer contains, relative to 100% by mass of the colored layer, 5 to 30% by mass of a polylactic acid resin, 40 to 92% by mass of an aliphatic aromatic polyester resin, and further contains carbon black.

[0039] Similarly, when a film is prepared by laminating a reflective layer and a colored layer, the multilayer film contains 5 to 30 mass % of polylactic acid resin and 40 to 92 mass % of aliphatic aromatic polyester resin relative to 100 mass % of the multilayer film.

[0040] As described above, even in the case of a multi-layer film, the carboxylic acid value is 25 mmol / kg or less. Similarly, the multilayer film of the present invention has a tear strength in the machine direction (MD) of 100 N / cm or more (measured by JIS K 6732 method (Elmendorf method)), and more preferably 200 N / cm or more. Furthermore, the multilayer film of the present invention has a breaking elongation in the transverse direction (TD) of 100% or more in a tensile test (based on JIS K 7127, tensile speed of 200 mm / min).

[0041] <Manufacturing method> The biodegradable resin film of the present invention is produced by mixing a biodegradable resin, an additive, and other components as necessary, as long as the effects of the present invention are not impaired, and then molding the mixture by a commonly used resin film manufacturing method. Examples of the manufacturing method of such a resin film include T-die molding, inflation molding, and calendar molding. In addition, the film may be unstretched or uniaxially or biaxially stretched.

[0042] The biodegradable resin film of the present invention has the above-mentioned carboxylic acid value, tear strength in the machine direction (MD), and elongation at break in the transverse direction (TD), and is therefore particularly suitable for agricultural applications, for example as a mulch film. EXAMPLES

[0043] The present invention will be described in more detail below with reference to examples, but is not limited to these examples.

[0044] [Preparation of biodegradable resin film] The components were mixed in the mixing ratios shown in Table 1 below, and films having a thickness of 20 μm were formed by inflation molding in Examples 1 to 5 and Comparative Examples 1 to 4. The various conditions for the inflation molding were as follows. Cylinder temperature: 160~190℃ Die temperature: 165℃ Die diameter: 100mmφ Take-up speed: 5~15m / min Blow ratio: 2~3

[0045] [Table 1]

[0046] (biodegradable resin) PBAT1: carboxylic acid value 10, Mn 4.2×10 4 , Mw 1.2×10 5 PBAT2: Carboxylic acid value 25, Mn 5.3×10 4 , Mw 1.4×10 5 PBAT3: Carboxylic acid value 48, Mn 4.1×10 4 , Mw 1.3×10 5 PLA: Polylactic acid

[0047] (Additives) Talc: talc UVA: Ultraviolet absorber HALS: Light Stabilizers Amide: stearic acid amide

[0048] <Carboxylic acid value measurement> Approximately 1.0 g of sample and 20 mL of o-cresol dissolved in a hot water bath were placed in a 50 mL screw-top glass bottle. The container was covered and stirred at 110°C until the sample was completely dissolved. Next, 20 mL of dichloromethane was added and stirred until homogenous, and then 1 mL of potassium chloride solution (0.01 mol / L) was added and stirred well until completely dissolved. The solution was titrated with potassium hydroxide ethanol solution (0.05 mol / L) using a potentiometric titrator (AT-610, Kyoto Electronics Manufacturing Co., Ltd.). A blank (a solution without dissolved sample) was also titrated in the same manner as the sample. From the results, the titration amount required for neutralization was determined, and then the carboxylic acid value was calculated using the following formula (1). The results are shown in Table 1.

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[0049] <Measurement of tear strength> The tear strength was measured by the JIS K 6732 method (Elmendorf method). The measured tear strength (mN) was divided by the film thickness (20 μm) to obtain the tear strength (N / cm) of the present invention, which is summarized in Table 1 according to the following ranks. Tear strength in MD (machine direction) and TD (transverse direction) ◎:200N / cm or more ○: 100N / cm or more, less than 200N / cm ×: Less than 100N / cm Difference in tear strength between MD and TD ◎: 200 or less, 〇: More than 200, less than 600 ×: Over 600

[0050] <Measurement of elongation at break> The obtained biodegradable resin film was left to stand for one week under humid heat conditions (temperature 70°C, relative humidity 95%) to carry out an accelerated test. In a tensile test (based on JIS K 7127, tensile speed 200 mm / min), the elongation at break in the TD (transverse) direction was measured. The measurement results are summarized in Table 1 according to the following ranks. 〇: 100% or more ×: Less than 100%

Claims

1. A biodegradable resin film that does not contain a plasticizer and contains a biodegradable resin and an additive, The biodegradable resin contains an aliphatic aromatic polyester resin and a polylactic acid resin, and contains 5 to 30 mass% of the polylactic acid resin and 40 to 92 mass% of the aliphatic aromatic polyester resin relative to 100 mass% of the biodegradable resin film; The biodegradable resin film has a carboxylic acid value calculated by the following formula (1) of 25 mmol / kg or less, A biodegradable resin film suitable for agricultural mulch film. [0010]

2. 2. The biodegradable resin film according to claim 1, wherein the tear strength of the film in the longitudinal direction (MD direction) is 100 N / cm or more in an Elmendorf tear test.

3. The biodegradable resin film according to claim 1 or 2, wherein the polylactic acid-based resin is polylactic acid (PLA), and the aliphatic aromatic polyester-based resin is polybutylene adipate terephthalate (PBAT).

4. 3. The biodegradable resin film according to claim 1, characterized in that the film has a transverse (TD) breaking elongation of 100% or more after being left to stand for one week under conditions of a temperature of 70°C and a relative humidity of 95%.

5. The biodegradable resin film according to claim 3, characterized in that the elongation at break in the transverse direction (TD) is 100% or more after the film is left to stand for one week under conditions of a temperature of 70°C and a relative humidity of 95%.

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