JP2024064297A - Biodegradable resin composition and resin molding using the same - Google Patents

Abstract

To provide a biodegradable resin composition which is excellent in moldability and handleability and has good dispersibility, and a resin molding using the same.SOLUTION: A biodegradable resin composition contains a biodegradable resin and inorganic substance powder. A mass ratio of the biodegradable resin to the inorganic substance powder is 70:30 to 90:10, the biodegradable resin contains polybutylene adipate terephthalate and a polybutylene succinate-based resin, and the inorganic substance powder contains calcium carbonate and a talc. The calcium carbonate is particles satisfying 50% particle diameter in a prescribed range, a specific surface area by an air permeability method, and a sieve residue of a JIS standard sieve, and the talc is particles satisfying 50% particle diameter in a prescribed range and a BET specific surface area.SELECTED DRAWING: None

Description

The present invention relates to a biodegradable resin composition and a resin molded body using the same.

Biodegradable resins, such as polylactic acid (PLA), can be decomposed into substances that naturally occur in nature through hydrolysis and microbial metabolism in the environment. For this reason, biodegradable resins have attracted attention and are widely used as environmentally friendly resins, and further expansion of their applications is expected in the future.

PLA has mechanical strength comparable to that of general-purpose plastics. However, it has poor heat resistance compared to petrochemical polyesters such as polyethylene terephthalate and polybutylene terephthalate. PLA also has relatively good hardness, but it lacks flexibility and processability, and it has been pointed out that it has a high specific gravity and is not very lightweight. In addition, in recent years, it has become difficult to obtain PLA due to increased demand, and there are concerns about rising costs.

In general, biodegradable resins have high resin viscosity, a narrow temperature range in which they can be handled, and poor moldability due to their adhesiveness. In addition, the manufacturing costs are high, and this is another major issue for biodegradable resins to become widespread as an alternative to petrochemical-based plastics.

It has also been pointed out that when PLA is used as a raw material, it is prone to thermal decomposition due to the need to mold it at high temperatures and keep it in a molten state for a long period of time, making it extremely difficult to mold and process.

Furthermore, in films made of PLA, the rate-limiting hydrolysis reaction is relatively slow at room temperature, and it takes a considerable amount of time for microorganisms to assimilate it. Particularly in agricultural films (mulch films), decomposition proceeds from the film surface due to the action of enzymes by microorganisms in the soil. For this reason, depending on the conditions, it can take a considerable amount of time for the biodegradable resin that makes up the film to completely decompose, and there is concern that it may remain in the soil for a long period of time after being ploughed in. In other words, the biodegradable properties are not being fully utilized, and further improvements are desired.

On the other hand, Patent Documents 1 and 2 state that a resin composition combining polybutylene adipate terephthalate (PBAT) and PLA with calcium carbonate and talc is useful as a film such as a mulch film.

However, when the polyester films described in these documents are formed into thin films of less than 30 μm, the film elongation, especially in the MD (extrusion) direction, is insufficient, and they lack versatility. In addition, it has been pointed out that the processing temperature of PLA is high, so drawdown is likely to occur during compounding, resulting in poor processability. Furthermore, the melting points of PBAT and PLA are significantly different from each other. For this reason, it is difficult to knead these resins uniformly when blending them, and there is concern that this may lead to variation in the mechanical properties of the resulting polyester film.

International Publication No. 2014/075998 International Publication No. WO 2012/152820

The present invention aims to solve the above problems, and its purpose is to provide a biodegradable resin composition that has excellent moldability and handleability, and also has good degradability, and a resin molded article made using the same.

The present invention provides a biodegradable resin composition containing a biodegradable resin and an inorganic substance powder,
the mass ratio of the biodegradable resin to the inorganic substance powder is 70:30 to 90:10;
the biodegradable resin comprises polybutylene adipate terephthalate and polybutylene succinate-based resins, and the inorganic powder comprises calcium carbonate and talc;
The calcium carbonate particles satisfy the following (1) to (3):
0.8≦A1≦3.0 (1)
13,000≦B≦30,000 (2)
C≦10 (3)
(here,
A1 is the 50% particle size (d50) (μm) measured by a Microtrac MT3300 laser particle size distribution analyzer;
B is the specific surface area ( ^cm2 /g) measured by the air permeability method, and C is the sieve residue (ppm) of a JIS standard sieve with an opening of 45 μm.
and
The talc particles satisfy the following (4) to (5):
1.0≦A2≦10.0 (4)
D/A2≦4.0 (5)
(here,
A2 is the 50% particle size (d50) (μm) measured by a Microtrac MT3300 laser particle size analyzer, and D is the BET specific surface area ( ^m2 /g).
The composition is:

In one embodiment, the polybutylene succinate-based resin is at least one resin selected from the group consisting of polybutylene succinate adipate and polybutylene succinate.

In one embodiment, the polybutylene adipate terephthalate has a weight average molecular weight of 50,000 to 300,000 and is contained in an amount of 50% to 95% by mass based on the mass of the biodegradable resin.

In one embodiment, the present invention is a resin molded product containing the biodegradable resin composition.

In one embodiment, the resin molded article of the present invention has the form of a film.

In one embodiment, the resin molding of the present invention has the form of an agricultural film.

According to the present invention, resin molded products such as films can be easily obtained. The obtained resin molded products have excellent mechanical strength and enhanced degradability. For example, when molded into agricultural film and used, the components remaining after biodegradation in soil do not contaminate the soil, and biodegradation can be promoted in a relatively short period of time.

(Biodegradable resin composition)
The biodegradable resin composition of the present invention contains a biodegradable resin and an inorganic substance powder.

(Biodegradable resin)
In the present invention, biodegradable resins include polybutylene adipate terephthalate (PBAT) and polybutylene succinate based resins.

PBAT is a biodegradable random copolymer, specifically a copolyester whose monomer components are adipic acid, 1,4-butanediol, and terephthalic acid. PBAT is highly biodegradable among known biodegradable resins, and is commercially available. PBAT also has a well-balanced combination of physical properties such as strength and heat resistance, and is known to have physical properties similar to those of general-purpose polyethylene. For this reason, it can be easily molded using general-purpose plastic molding methods.

The weight average molecular weight (MW) of PBAT is preferably 50,000 to 300,000, more preferably 100,000 to 200,000. PBAT with a weight average molecular weight within this range generally has an excellent balance of physical properties such as biodegradability, moldability, and strength.

PBAT is preferably contained in an amount of 50% by mass to 95% by mass, more preferably 70% by mass to 95% by mass, and even more preferably 80% by mass to 95% by mass, based on the mass of the biodegradable resin constituting the composition of the present invention. Polybutylene adipate terephthalate (PBAT) is highly biodegradable among various biodegradable resins, and is easily available because it is mass-produced. It also has an excellent balance of physical properties such as strength and heat resistance, and since its physical properties are close to those of general-purpose polyethylene, it can be molded by general-purpose plastic molding methods. Therefore, it is easy to modify the biodegradable resin composition into a resin with preferred physical properties depending on the application, etc.
If the PBAT content exceeds 95% by mass, the resulting resin composition becomes too soft, and cutting of the composition when pelletized may become difficult.

Examples of polybutylene succinate-based resins include polybutylene succinate adipate (PBSA) and polybutylene succinate (PBS), as well as combinations thereof.

PBSA is a copolyester whose monomer components are adipic acid, 1,4-butanediol, and succinic acid, and is commercially available as a plant-derived biodegradable plastic. PBSA is also known to have excellent moldability.

PBS is a copolyester made of succinic acid and 1,4-butanediol as monomer components, and is commercially available as a plant-derived biodegradable plastic. PBS is also known for its excellent heat sealability, compatibility, heat resistance, and flexibility.

The polybutylene succinate resin is preferably 50% by mass to 5% by mass, more preferably 30% by mass to 5% by mass, and even more preferably 20% by mass to 5% by mass, based on the mass of the biodegradable resin constituting the composition of the present invention.

In the present invention, the polybutylene adipate terephthalate (PBAT) is used in combination with a polybutylene succinate resin, which improves the moldability of the resulting resin composition and makes it easier to adjust the flexibility of the film. In particular, when spreading a mulch film, the flexibility of the film is an important property because the adaptability of the film to the ridge surface is affected in areas with hard soil and areas with soft soil. Therefore, by being able to impart an appropriate degree of flexibility to the film, the mulch film obtained from the resin composition of the present invention is free from the limitations of the area of use that depend on the hardness of the soil.

The biodegradable resin may contain a resin having biodegradability other than those mentioned above (other biodegradable resins). Examples of other biodegradable resins include polyhydroxyalkanoate (PHA), 3-hydroxybutyric acid-3-hydroxyhexanoic acid copolymer polyester (PHBH), starch polyester resin, cellulose acetate (diacetate), polyvinyl alcohol (PVA), polyglycolic acid (PGA), and polyethylene terephthalate succinate (PETS), as well as combinations thereof. An appropriate content of other biodegradable resins can be selected by those skilled in the art within a range that does not inhibit the effects of the present invention provided by the PBAT and polybutylene succinate resins mentioned above.

The melt flow rate (MFR) of the biodegradable resin is preferably 0.1 g/10 min to 10 g/10 min, as measured at 190°C under a load of 2.16 kg according to JIS K7210 (1999). From the viewpoint of moldability and mechanical strength, the MFR of the biodegradable resin is more preferably 8 g/10 min or less, and particularly preferably 6 g/10 min or less. If the MFR is higher than 10 g/10 min, molding processing using a film-forming machine becomes difficult. The MFR of the biodegradable resin can be adjusted by the molecular weight.

(Inorganic powder)
In the present invention, the inorganic powder can function as, for example, an inorganic filler. Here, the mass ratio (mass%) of the above-mentioned biodegradable resin contained in the biodegradable resin composition of the present invention to the inorganic powder is 70:30 to 90:10, preferably 75:25 to 90:10, and more preferably 75:25 to 85:15. Here, if the ratio of the inorganic powder is less than 10 mass% in the range of the mass ratio of the biodegradable resin to the inorganic powder, the release property of the film obtained from such a resin composition may deteriorate, the processability may be poor, and further the biodegradable physical properties may not be fully exhibited. If the ratio of the inorganic powder is more than 30 mass% in the range of the mass ratio of the biodegradable resin to the inorganic powder, the strength of the film obtained from such a resin composition may decrease when the film is thinned.

The inorganic powder must contain calcium carbonate and talc.

Calcium carbonate and talc can increase the surface area of the resulting film. Furthermore, when the biodegradable resin composition of the present invention decomposes in soil, calcium carbonate and talc fall off as appropriate, which makes it possible to increase the area of contact between the biodegradable resin portion remaining after they fall off and the decomposition enzymes produced by microorganisms in the soil. As a result, it is expected that the biodegradation rate of the biodegradable resin, which is a component of the composition, will be further increased.

From this perspective, the use of calcium carbonate and talc, which have stable quality and price and are available in large quantities industrially, is economically advantageous and also effectively improves moldability, making it possible to provide a biodegradable resin composition with excellent biodegradability and good moldability and productivity.

(Calcium Carbonate)
The calcium carbonate that can constitute the inorganic substance powder may be so-called heavy calcium carbonate obtained by mechanically crushing limestone, or may be precipitated calcium carbonate that can be obtained by, for example, a carbon dioxide gas compounding method. From the viewpoints of workability and cost, the calcium carbonate is preferably heavy calcium carbonate. Limestone, which is the raw material for calcium carbonate, is abundantly produced in Japan in high purity and can be obtained very economically. As the calcium carbonate, one type may be used alone, or two or more types may be used in combination.

To enhance the dispersibility or reactivity of calcium carbonate, the surface of calcium carbonate particles may be modified in advance. Examples of surface modification methods include physical methods such as plasma treatment, and chemical surface treatment with a coupling agent or surfactant. Examples of coupling agents include silane coupling agents and titanium coupling agents. Examples of surfactants include anionic, cationic, nonionic, and amphoteric surfactants, and examples of such surfactants include higher fatty acids, higher fatty acid esters, higher fatty acid amides, and higher fatty acid salts.

By applying the above-mentioned surface modification, it is possible to improve the dispersibility of calcium carbonate. On the other hand, calcium carbonate that has not been surface modified may be preferable in that it reduces the risk of odor generation due to thermal decomposition of the surface treatment agent during molding.

The calcium carbonate constituting the inorganic substance powder is, for example, preferably 5% by mass to 95% by mass, more preferably 10% by mass to 90% by mass, and particularly preferably 20% by mass to 80% by mass, based on the mass of the inorganic substance powder.

In the present invention, the 50% particle size (d50) A1 of calcium carbonate is 0.8 μm to 3.0 μm, preferably 1.0 μm to 2.8 μm, more preferably 1.3 μm to 2.5 μm, and particularly preferably 1.6 μm to 2.2 μm, as measured by a Microtrac MT3300 laser particle size distribution analyzer. If the 50% particle size (d50) is less than 0.8 μm, the calcium carbonate particles themselves become too fine, resulting in an increase in their surface area and poor handling properties, and for example, the viscosity of the composition when kneaded with the biodegradable resin increases significantly, making it difficult to manufacture a film. If the 50% particle size (d50) is more than 3.0 μm, for example, when a biodegradable film is molded, the calcium carbonate particles may protrude from the film surface and fall off, or the surface properties and mechanical strength may be impaired. In particular, it is preferable that the calcium carbonate does not contain particles with a 50% particle size (d50) of 45 μm or more in its particle size distribution.

Methanol can be used as a solvent to measure the 50% particle size (d50). Furthermore, when performing the measurement, an ultrasonic disperser, Ultra Sonic Generator US-300T manufactured by Nippon Seiki Seisakusho Co., Ltd., can be used to pre-disperse the methanol slurry used for the measurement.

In the present invention, the specific surface area B of calcium carbonate measured by the air permeation method is 13,000 cm ² /g to 30,000 cm ² /g, preferably 15,000 cm ² /g to 25,000 cm ² /g, and more preferably 18,000 cm ² /g to 23,000 cm ² /g. By having a specific surface area within this range, the physical properties of the molded article obtained are improved, and the molded article has many surfaces that serve as starting points for biodegradation reactions, which can promote biodegradability in a natural environment. On the other hand, it is also possible to suppress a decrease in the processability of the resin composition due to the incorporation of calcium carbonate particles.

The specific surface area of calcium carbonate by the air permeability method can be measured, for example, using a constant pressure powder specific surface area device (SS-100, manufactured by Shimadzu Corporation) under the following measurement conditions.
Specific gravity of calcium carbonate: 2.7 g/mL
Sample: 2.7 g
Amount of water passed: 5 mL
Thickness of sample layer: If the specific surface area is less than 10,000 cm ² /g, adjust to 8-9 mm. If the specific surface area is 10,000 cm ² /g or more and 20,000 cm ² /g or less, adjust to 9-12 mm. If the specific surface area is more than 20,000 cm ² /g, adjust to between 12-13 mm.

In the present invention, such calcium carbonate has the form of calcium carbonate particles. The calcium carbonate content in the calcium carbonate particles is preferably 95% by mass or more, more preferably 97% by mass or more, and even more preferably 99% by mass or more. By making the calcium carbonate content in the calcium carbonate particles 95% by mass, that is, by making the calcium carbonate particles highly pure, it is possible to suppress the impact on the human body and the environment, and to reduce wear on the molding and processing machines.

The purity of the calcium carbonate can be measured according to JIS K8617 calcium carbonate.

Furthermore, in the present invention, the calcium carbonate has a sieve residue C of 10 ppm or less, preferably 5 ppm or less, when measured using a JIS standard sieve with a mesh size of 45 μm by the sieve test method described below. If the sieve residue C exceeds 10 ppm, there is a concern that the film strength may decrease and fish eyes may be more likely to occur when the film is made thinner.

The sieve test method for measuring sieve residue C is as follows:

First, 500 g of sample is weighed into a 2 L stainless steel beaker, and 1000 g of industrial methanol is added to prepare a slurry. Next, this slurry is poured onto a JIS standard sieve with an inner diameter of 200 mm and mesh size of 45 μm, while being lightly mixed with a brush to allow the sample to pass through. Any solid matter adhering to the brush is washed off with water, and the sieve is lightly swept with the brush until the liquid that passed through the sieve becomes completely transparent. Next, the residue is transferred to a JIS standard sieve with an inner diameter of 75 mm and mesh size of 45 μm, and left in a dryer (105°C) for at least 30 minutes. After that, it is left to cool in a desiccator for 15 minutes, after which the residue is placed on a medicine wrapping paper and the amount of residue remaining on the sieve is calculated.

(talc)
Talc, which can be used to make up the inorganic powder, is a powder of talc, which contains water, silicon, oxygen, magnesium, etc. and is also called hydrated magnesium silicate. It is a smooth inorganic material with excellent adsorption properties.

The talc constituting the inorganic substance powder is, for example, preferably 5% by mass to 95% by mass, more preferably 10% by mass to 90% by mass, and particularly preferably 20% by mass to 80% by mass, based on the mass of the inorganic substance powder.

In the present invention, the 50% particle size (d50) A2 of talc is 1.0 μm to 10.0 μm, preferably 2.0 μm to 8.0 μm, and more preferably 3.0 μm to 5.0 μm, when measured by a Microtrac MT3300 laser type particle size distribution analyzer. If the 50% particle size (d50) is less than 1.0 μm, the talc particles themselves become too fine, their surface area increases, and handling properties deteriorate. For example, when kneaded with the above-mentioned biodegradable resin, the viscosity of the composition increases significantly, and film production may become difficult. If the 50% particle size (d50) exceeds 10.0 μm, for example, when a biodegradable film is molded, the talc particles may protrude from the film surface and fall off, or the surface properties and mechanical strength may be impaired. In particular, it is preferable that the talc does not contain particles with a 50% particle size (d50) of 45 μm or more in its particle size distribution.

In the present invention, the aspect ratio (D/A2), which is the value obtained by dividing the BET specific surface area D of the talc by the 50% particle size (d50) A2, is preferably 4.0 or less, and more preferably 3.0 or less. By making D/A2 4.0 or less, it becomes easy to knead the talc into the resin, and the talc acts as a crystal nucleating agent to improve the elastic modulus of the obtained film, thereby maintaining high film strength.

The BET specific surface area D of the talc can be measured, for example, using a BET specific surface area measuring device (Macsorb, manufactured by Mountech) as follows:

First, 0.2 g to 0.3 g of the talc to be measured is loaded into the measuring device, and as a pretreatment, a heat treatment is performed at 200°C for 5 minutes in a mixed gas atmosphere of nitrogen and helium. The specific surface area can then be measured by performing low-temperature, low-humidity physical adsorption in a liquid nitrogen environment.

Other inorganic powders that can function as inorganic fillers include anhydrous silica, mica, clay, titanium oxide, diatomaceous earth, allophane, bentonite, potassium titanate, zeolite, sepiolite, smectite, kaolin, kaolinite, glass, limestone, carbon, wollastonite, calcined perlite, silicates such as calcium silicate and sodium silicate, quicklime, aluminum oxide, magnesium carbonate, hydroxides such as calcium hydroxide, ferric carbonate, zinc oxide, iron oxide, aluminum phosphate, and barium sulfate, and combinations thereof.

(Other ingredients)
The biodegradable resin composition of the present invention may further contain any other components in addition to the above components, as long as the effects of the present invention are not impaired. Such other components may be used alone or in combination of two or more. The types and amounts of such components may be appropriately selected by those skilled in the art depending on the effects to be obtained.

Examples of other ingredients include plasticizers, fillers (excluding calcium carbonate and talc), colorants, lubricants, coupling agents, flow improvers, dispersants, antioxidants, UV absorbers, flame retardants, stabilizers, antistatic agents, and foaming agents.

More specific examples of other ingredients will be explained below.

Examples of plasticizers include acetyl tributyl citrate, triethyl citrate, triethyl citrate, acetyl triethyl citrate, dibutyl phthalate, diaryl phthalate, dimethyl phthalate, diethyl phthalate, di-2-methoxyethyl phthalate, dibutyl tartrate, o-benzoyl benzoate, diacetin, and epoxidized soybean oil, and combinations thereof.

The filler is composed of an inorganic material other than the calcium carbonate and talc, and contains, for example, carbonates (excluding calcium carbonate), sulfates, silicates, phosphates, borates, oxides, or hydrates of calcium, magnesium, aluminum, titanium, iron, zinc, etc. Examples of fillers include calcium oxide, calcium hydroxide, feldspar, quartz, magnesium carbonate, zinc oxide, titanium oxide, silica, alumina, kaolin, aluminum hydroxide, magnesium hydroxide, aluminum silicate, magnesium silicate, calcium silicate, aluminum sulfate, magnesium sulfate, calcium sulfate, magnesium phosphate, barium sulfate, silica sand, carbon black, molybdenum, diatomaceous earth, sericite, shirasu, calcium sulfite, sodium sulfate, potassium titanate, bentonite, wollastonite, and graphite, as well as combinations thereof. The filler may be synthetic or derived from natural minerals.

The colorant may be any of the known organic pigments, inorganic pigments, or dyes. Specific examples of colorants include organic pigments such as azo, anthraquinone, phthalocyanine, quinacridone, isoindolinone, diosadin, perinone, quinophthalone, and perylene pigments, inorganic pigments such as ultramarine, titanium oxide, titanium yellow, iron oxide (red oxide), chromium oxide, zinc oxide, and carbon black, and combinations thereof.

Lubricants that are known in the art may be used. Specific examples of lubricants include higher fatty acid-based, aliphatic hydrocarbon-based, fatty acid amide-based, and fatty acid ester-based lubricants. Fatty acid amide-based lubricants are preferred because they improve the dispersibility of the biodegradable resin and filler during molding, thereby increasing fluidity, and they improve mold releasability, roll release, and metal release, thereby increasing moldability. These may be used alone or in combination of two or more types.

As the antioxidant, phosphorus-based antioxidants, phenol-based antioxidants, pentaerythritol-based antioxidants, etc., can be used alone or in any combination. Specific examples of phosphorus-based antioxidants include phosphorus-based antioxidant stabilizers such as phosphites and phosphates.

Here, examples of phosphite esters include triesters, diesters, monoesters, etc. of phosphorous acid, such as triphenyl phosphite, trisnonylphenyl phosphite, and tris(2,4-di-t-butylphenyl) phosphite, as well as combinations thereof.

Phosphate esters include trimethyl phosphate, triethyl phosphate, tributyl phosphate, trioctyl phosphate, triphenyl phosphate, tricresyl phosphate, tris(nonylphenyl)phosphate, and 2-ethylphenyldiphenyl phosphate, and combinations thereof.

Phenolic antioxidants include alpha-tocopherol, butylated hydroxytoluene, sinapyl alcohol, vitamin E, n-octadecyl-3-(3,5-di-t-butyl-4-hydroxyphenyl)propionate, 2-t-butyl-6-(3'-t-butyl-5'-methyl-2'-hydroxybenzyl)-4-methylphenylacrylate, 2,6-di-t-butyl-4-(N,N-dimethylaminomethyl)phenol, 3,5-di-t-butyl-4-hydroxybenzylphosphonate diethyl ester, and tetrakis[3-(3-5-di-t-butyl-4-hydroxyphenyl)propionyloxymethyl]methane, and combinations thereof.

Examples of flame retardants include one or more combinations of halogen-based flame retardants, phosphorus-based flame retardants, and non-phosphorus non-halogen flame retardants such as metal hydrates. Examples of halogen-based flame retardants include halogenated bisphenol compounds such as halogenated bisphenylalkanes, halogenated bisphenylethers, halogenated bisphenylthioethers, and halogenated bisphenylsulfones, and bisphenol-bis(alkyl ether) compounds such as brominated bisphenol A, brominated bisphenol S, chlorinated bisphenol A, and chlorinated bisphenol S. Examples of phosphorus-based flame retardants include aluminum tris(diethylphosphonate), bisphenol A bis(diphenyl phosphate), triarylisopropyl phosphate, cresyl di-2,6-xylenyl phosphate, and aromatic condensed phosphate esters. Examples of metal hydrates include aluminum trihydrate and magnesium dihydroxide. In addition to these flame retardants, for example, antimony oxides such as antimony trioxide and antimony pentoxide, zinc oxide, iron oxide, aluminum oxide, molybdenum oxide, titanium oxide, calcium oxide, magnesium oxide, etc. may be used in combination as flame retardant assistants.

The foaming agent is mixed or injected into the raw biodegradable resin composition in a molten state in a melt kneader, and changes phase from solid to gas or liquid to gas, or is a gas itself, and is mainly used to control the expansion ratio (foam density) of the foam sheet. The foaming agent dissolved in the biodegradable resin composition of the present invention changes phase to gas depending on the resin temperature and dissolves in the molten resin, while the foaming agent dissolved in the biodegradable resin composition of the present invention does not change phase and dissolves in the molten resin as it is. When the molten resin is extruded into a sheet from the extrusion die, the foaming agent expands inside the sheet as the pressure is released, and a foam sheet can be provided in which a large number of fine independent bubbles are formed in the sheet. The foaming agent secondarily acts as a plasticizer that reduces the melt viscosity of the biodegradable resin composition of the present invention, and the temperature for plasticizing the biodegradable resin composition can be lowered.

Examples of blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane; alicyclic hydrocarbons such as cyclobutane, cyclopentane, and cyclohexane; halogenated hydrocarbons such as chlorodifluoromethane, difluoromethane, trifluoromethane, trichlorofluoromethane, dichloromethane, dichlorofluoromethane, dichlorodifluoromethane, chloromethane, chloroethane, dichlorotrifluoroethane, dichloropentafluoroethane, tetrafluoroethane, difluoroethane, pentafluoroethane, trifluoroethane, dichlorotetrafluoroethane, trichlorotrifluoroethane, tetrachlorodifluoroethane, and perfluorocyclobutane; inorganic gases such as carbon dioxide, nitrogen, and air; and water.

The biodegradable resin composition of the present invention may further contain quicklime and/or slaked lime as an additional component when it is desired to accelerate the biodegradability. Such additional components can accelerate the biodegradability of the resulting biodegradable resin composition. In general, the biodegradability of a biodegradable resin varies depending on factors such as bacteria in the soil, temperature, and humidity. For this reason, when a use such as a mulch film is planned, it is desirable to carry out a preliminary experiment in the on-site environment in which the composition will be installed in advance and determine the amount of the additional component to be added. The quicklime or slaked lime preferably has a sieve residue of 0.5% or less, more preferably 0.3% or less, on a JIS standard sieve with a mesh size of 75 μm. If the sieve residue exceeds 0.5%, the strength of the film may decrease when the film is thinned, and fish eyes may occur.

(Preparation of biodegradable resin composition)
The biodegradable resin composition of the present invention can be produced using the above-mentioned components, for example, based on a method conventionally known as a method for producing a resin composition.

The biodegradable resin composition of the present invention can be obtained, for example, by mixing the components and melt-kneading them.

The timing of mixing and melt-kneading can be set appropriately depending on the molding method to be adopted (extrusion molding, injection molding, vacuum molding, etc.). For example, the biodegradable resin, calcium carbonate and/or talc may be kneaded and melted before being fed from a hopper into a molding machine, or the biodegradable resin, calcium carbonate and/or talc may be kneaded and melted simultaneously with molding in an integrated molding machine. The kneading and melting is preferably performed by applying high shear stress while uniformly dispersing the calcium carbonate and/or talc in the biodegradable resin, for example, by kneading with a twin-screw kneader.

The form of the biodegradable resin composition obtained is not particularly limited, and may be, for example, in the form of pellets. When the biodegradable resin composition of the present invention is in the form of pellets, the form is not particularly limited, and may be, for example, cylindrical, spherical, elliptical, or the like. The granulation process for obtaining pellets may be carried out by a procedure or device commonly used by the person concerned. For example, while melting the biodegradable resin using a twin-screw extruder or the like, calcium carbonate and talc, as well as the above-mentioned other components as necessary, are added and melt-kneaded, extruded into a strand shape, cooled, and then processed into pellets using a pelletizer. The obtained pellets can be sufficiently dried to remove moisture, and then molded to obtain the desired film.

In the present invention, the size of the pellets is not particularly limited. For example, when the pellets are in the form of spherical pellets, the diameter may be 1 mm to 10 mm. When the pellets are in the form of elliptical pellets, the aspect ratio may be 0.1 to 1.0, and the length and width may be 1 mm to 10 mm. When the pellets are in the form of cylindrical pellets, the diameter may be 1 mm to 10 mm and the length may be 1 mm to 10 mm.

(Resin Molded Body)
Any molded article can be obtained from the biodegradable resin composition of the present invention. For example, the biodegradable resin composition of the present invention can be molded into a film.

The following describes how to mold the biodegradable resin composition of the present invention into a film.

When forming the film, a film-forming machine used in the known inflation method or T-die method can be used. The film obtained using the biodegradable resin composition of the present invention is suitable for use as, for example, a mulch film, and has a good balance of tensile strength. For this reason, it is particularly preferable to manufacture it using the inflation method.

The thickness of the film that can be produced by the present invention is preferably 0.005 mm to 0.030 mm, and more preferably 0.01 mm to 0.025 mm. Films with a thickness of less than 0.005 mm may not have sufficient mechanical strength to be used as biodegradable films. Films with a thickness of more than 0.030 mm may be difficult to bury in soil with a hoe or the like after use in order to promote efficient biodegradation in soil.

The molding conditions for obtaining the above-mentioned film can be appropriately selected by a person skilled in the art depending on the composition of the biodegradable resin composition used, the type of molded product, etc.

The film thus obtained may be stretched uniaxially, biaxially, or multiaxially during or after molding.

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

(Evaluation method)
The physical properties in the following Examples 1 to 8 and Comparative Examples 1 to 10 were obtained by the following methods.

(Measurement of Melt Flow Rate (MFR) of Resin)
The melt flow rate (MFR) of the resin was measured at 190° C. and a load of 2.16 kg using a melt indexer in accordance with JIS K7210 (1999). The unit was g/10 min.

(Weight average molecular weight (Mw))
The weight average molecular weight was obtained by converting it into a standard polystyrene value by gel permeation chromatography (GPC). The measuring instruments used were a differential refractometer (RID-6A manufactured by Shimadzu Corporation) as a detector, a pump (LC-10AT manufactured by Shimadzu Corporation), and a column (TSKgel G2000HXL, TSKgel G3000HXL and TSKguard column HXL-L manufactured by Tosoh Corporation connected in series). Chloroform was used as the eluent, and 6 μL of a sample with a temperature of 40° C., a flow rate of 1.0 mL/min, and a concentration of 1 mg/mL was injected.

(Compounding)
First, for the Examples and Comparative Examples, the raw materials having the compounding ratios shown in Table 1 were mixed at 170°C, 250 rpm screw rotation speed, and 22 kg/hour extrusion rate using a co-rotating twin screw extruder (D=32 mmφ, L/D=60, manufactured by Plastics Engineering Research Institute Co., Ltd.), extruded into water as a strand, cooled, cut, and prepared into pellets. The unit of the composition values in Table 1 is "mass %".

The pellets obtained were extruded from a T-die at 170°C using a film extruder (Labo Plastomill 2D30W2, manufactured by Toyo Seiki Co., Ltd.) to obtain an unstretched mulch film with a thickness of 15 μm. A strength test was conducted using test pieces made from the obtained mulch film. The results are shown in Table 1.

(Evaluation of biodegradable films)
The biodegradable films obtained above were evaluated for (i) tensile strength and elongation (MD: extrusion direction, TD: transverse direction), (ii) biodegradability, and (iii) film formability by the following methods to evaluate whether they were suitable for use as agricultural films. The results are shown in Table 1.
(1) Tensile strength and elongation: Measured in accordance with JIS K6781.
(2) Biodegradability: Biodegradability under compost conditions was measured in accordance with JIS K6953.
(3) Film-forming property: Evaluated according to the following criteria.
◯: Films could be produced continuously without any problems.
Δ: A film could be formed, but stability was difficult.
×: Film formation was not possible.

(material)
The components used in the following Examples 1 to 8 and Comparative Examples 1 to 10 were as follows.

(Biodegradable resin)
P1: Polybutylene adipate terephthalate TH801T manufactured by Miyako Chemical Co., Ltd., weight average molecular weight Mw: 106,000, MFR: 5.0 g/10 min, melting point: 120° C.
P2: Polybutylene succinate BioPBS FZ91 manufactured by PTTMCC Biochem, MFR: 5.0 g/10 min, melting point: 113° C.
P3: Polylactic acid Luminy LX175 manufactured by Total Cabion, MFR: 3.0 g/10 min, melting point: 155° C.

(Calcium Carbonate)
Calcium carbonate 1: MC Coat S-20 manufactured by Maruo Calcium Co., Ltd. (average particle size: 2.0 μm, specific surface area: 20,000 cm ² /g, 45 μm sieve residue: 1 ppm or less)
Calcium carbonate 2: Caltex S-5A manufactured by Maruo Calcium Co., Ltd. (average particle size: 1.0 μm, specific surface area: 26,000 cm ² /g, 45 μm sieve residue: 1 ppm or less)
Calcium carbonate 3: MC Coat S-17 manufactured by Maruo Calcium Co., Ltd. (average particle size: 2.6 μm, specific surface area: 15,600 cm ² /g, 45 μm sieve residue: 8 ppm)
Calcium carbonate 4: Super SSS manufactured by Maruo Calcium Co., Ltd. (average particle size: 4.0 μm, specific surface area: 12,000 cm ² /g, 45 μm sieve residue: 10 ppm)
Calcium carbonate 5: Kalfine YM-23 manufactured by Maruo Calcium Co., Ltd. (average particle size: 0.6 μm, specific surface area: 40,000 cm ² /g, 45 μm sieve residue: 1 ppm or less)
Calcium carbonate 6: MC Coat S-15 manufactured by Maruo Calcium Co., Ltd. (average particle size: 2.9 μm, specific surface area: 13,100 cm ² /g, 45 μm sieve residue: 12 ppm)

(talc)
Talc 1: FH-105 manufactured by Fuji Talc Co., Ltd. (aspect ratio = D/A2 = 2.0, average particle size: 4.7 μm, BET specific surface area: 9.5 m ² /g)
Talc 2: MS412 manufactured by Fuji Talc Co., Ltd. (aspect ratio = D/A2 = 0.375, average particle size: 12 μm, BET specific surface area: 4.5 m ² /g)

(Tensile strength and elongation at break)
Tensile tests of the test pieces prepared by the film extruder were carried out at a temperature of 23°C using a precision universal testing machine manufactured by Shimadzu Corporation. The shape of the test piece used was a dumbbell-shaped test piece according to JIS K7161:2014. The stretching speed was 50 mm/min. The tensile strength (unit: MPa) and elongation at break (unit: %) were measured from the obtained stress-strain curve.

The higher the values of tensile strength and elongation at break, the better the tensile strength and elongation at break. The evaluation criteria for tensile strength and elongation at break are as follows:

(Evaluation Criteria for Tensile Strength)
A: The tensile strength was 30 MPa or more.
B: The tensile strength was 25 MPa or more and less than 30 MPa.
C: The tensile strength was 20 MPa or more and less than 25 MPa.
D: The tensile strength was less than 20 MPa.

(Evaluation Criteria for Elongation at Break)
A: The elongation at break was 300% or more.
B: The elongation at break was 250% or more and less than 300%.
C: The elongation at break was 200% or more and less than 250%.
D: The tensile strength was less than 200%.

As shown in Table 1, in Examples 1 to 8, in which biodegradable resin and inorganic powder were mixed in a mass ratio of 70:30 to 90:10 according to the present invention, films with excellent moldability and biodegradability were obtained.

On the other hand, Comparative Example 2, which had a low blend ratio of inorganic powder, and Comparative Example 1, which had no inorganic powder blend, had significantly poor moldability and insufficient biodegradability. Comparative Example 3, which had an extremely high blend ratio of inorganic powder, had significantly poor film strength. Comparative Example 4, in which polylactic acid (PLA) was blended with the biodegradable resin, had reduced elongation in the MD direction and was also insufficient in biodegradability. Comparative Examples 5 and 6, in which calcium carbonate or talc was blended alone with the inorganic powder, were not fully satisfactory in both film strength and elongation.

Comparative Example 7, in which the average particle size of calcium carbonate was large, Comparative Example 10, in which the average particle size of talc was large, and Comparative Example 9, in which the calcium carbonate had a large amount of 45 μm sieve residue, were significantly inferior in moldability and tensile strength. Comparative Example 8, in which the average particle size of calcium carbonate was small, had non-uniform film formability, significantly inferior moldability, and reduced MD elongation.

In the above test, when a biodegradable resin made of PBSA was used instead of biodegradable resin P2, it was confirmed that similar results to those described above were obtained.

The present invention is useful, for example, in the fields of resin molding, agriculture, and a wide range of related technical fields.

Claims (6)

A biodegradable resin composition comprising a biodegradable resin and an inorganic substance powder,
the mass ratio of the biodegradable resin to the inorganic substance powder is 70:30 to 90:10;
the biodegradable resin comprises polybutylene adipate terephthalate and polybutylene succinate-based resins, and the inorganic powder comprises calcium carbonate and talc;
The calcium carbonate particles satisfy the following (1) to (3):
0.8≦A1≦3.0 (1)
13,000≦B≦30,000 (2)
C≦10 (3)
(here,
A1 is the 50% particle size (d50) (μm) measured by a Microtrac MT3300 laser particle size distribution analyzer;
B is the specific surface area ( ^cm2 /g) measured by the air permeability method, and C is the sieve residue (ppm) of a JIS standard sieve with an opening of 45 μm.
and
The talc particles satisfy the following (4) to (5):
1.0≦A2≦10.0 (4)
D/A2≦4.0 (5)
(here,
A2 is the 50% particle size (d50) (μm) measured by a Microtrac MT3300 laser particle size analyzer, and D is the BET specific surface area ( ^m2 /g).
The composition. The biodegradable resin composition according to claim 1, wherein the polybutylene succinate-based resin is at least one resin selected from the group consisting of polybutylene succinate adipate and polybutylene succinate. The biodegradable resin composition according to claim 1, wherein the polybutylene adipate terephthalate has a weight average molecular weight of 50,000 to 300,000 and is contained in an amount of 50% by mass to 95% by mass based on the mass of the biodegradable resin. A resin molded body containing the biodegradable resin composition according to any one of claims 1 to 3. The resin molded article according to claim 4, which has the form of a film. The resin molded product according to claim 5, which has the form of an agricultural film.