Method for producing composite powder, and method for producing biodegradable resin composition

Abstract

To provide a method for producing composite powder of biodegradable resin and organic powder in which generation of aggregate can be suppressed, and a method for producing a biodegradable resin composition in which organic powder is excellently dispersed.SOLUTION: A method for producing composite powder has a compounding step of inputting biodegradable resin and naturally derived organic powder into a high-speed mixer having rotating blades and mixing at high speed to obtain composite powder, and the compounding step is executed so as to satisfy all of the followings (A) to (C). (A) The proportion of the organic powder to be input into the high-speed mixer is 65 pts.mass or more and 900 pts.mass or less for the biodegradable resin 100 pts.mass. (B) The average peripheral speed of the rotating blades is 8 m / sec. to 20 m / sec., and mixing time is 7 minutes or more and 60 minutes or less. (C) The melting point T°C of the biodegradable resin is 50°C or more and 140°C or less, and the temperature inside the high-speed mixer is less than (T-20)°C when starting high-speed mixing and is (T+15)°C or more when ending high-speed mixing.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing a composite powder obtained by compounding an organic powder such as cellulose powder with a biodegradable resin, and a method for producing a biodegradable resin composition using the composite powder obtained by the method. [Background technology]

[0002] Currently, packaging materials such as packaging bags are often made of polyolefins such as polyethylene. However, polyolefin packaging bags have the problem of remaining undecomposed in the natural environment and becoming an environmental burden. To solve this problem, development of biodegradable resins is progressing. Here, biodegradability refers to the property of ultimately decomposing into water and carbon dioxide in the natural environment by the action of microorganisms.

[0003] Specifically, as disclosed in Patent Document 1, polyester-based biodegradable resins are known as biodegradable resins. Among them, aliphatic polyesters are known as resins that have a good balance of moldability and biodegradability. Examples of aliphatic polyesters include polybutylene succinate (hereinafter sometimes referred to as "PBS") and polybutylene succinate adipate (hereinafter sometimes referred to as "PBSA"), which are obtained by polycondensation of an aliphatic dicarboxylic acid and an aliphatic diol, as well as polycaprolactone obtained by ring-opening polymerization of ε-caprolactone. Other known polyester-based biodegradable resins include aliphatic-aromatic polyesters, such as polybutylene adipate terephthalate (hereinafter sometimes referred to as "PBAT"), which are obtained by polycondensation of an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and an aliphatic diol. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2005-15741 Summary of the Invention [Problem to be solved by the invention]

[0005] In recent years, marine pollution caused by discarded plastic products has become a problem. Therefore, plastic products are required to be biodegradable in seawater (marine biodegradable) in addition to being biodegradable in soil. However, plastic products made from the above-mentioned aliphatic polyesters and aliphatic-aromatic polyesters currently do not have sufficient marine biodegradability.

[0006] To solve the above problems, it has been considered to incorporate a biodegradable filler into the resin composition, thereby reducing the proportion of biodegradable resin in the resin composition and increasing the biodegradability of the resin composition. For example, if a biodegradable organic powder such as cellulose is used as the filler, the biodegradability of the entire resin composition can be expected to be improved, coupled with the biodegradability of the organic powder itself. However, organic powders such as cellulose powder have low dispersibility in resins, and simply mixing the two in a kneader or other mixer can result in the formation of aggregates. In particular, when molding a resin composition into a film by inflation molding, the presence of aggregates in the resin composition can cause problems such as the film breaking and making it impossible to form a film, or the mechanical properties being reduced.

[0007] It is possible to remove the aggregates in the resin composition by placing a filter inside the extruder. However, if the content of aggregates is high, the aggregates accumulate in the filter, causing an increase in pressure, and the aggregates accumulated on the filter may burn, causing discoloration of the extruded resin composition, or causing clogging within a short period of time.

[0008] Therefore, the present invention aims to provide a method for producing a composite powder of a biodegradable resin and an organic powder that can suppress the formation of aggregates, and to provide a method for producing a biodegradable resin composition in which the organic powder is well dispersed in the biodegradable resin. [Means for solving the problem]

[0009] In order to solve the above problems, a method for producing a composite powder according to one aspect of the present invention includes the steps of: The method includes a compounding step of mixing a biodegradable resin and a naturally-derived organic powder at high speed in a high-speed mixer having a rotary blade to obtain a composite powder, The composite step is carried out so as to satisfy all of the following conditions (A) to (C). (A) The ratio of the biodegradable resin and the organic powder to be charged into the high-speed mixer is 65 parts by mass or more and 900 parts by mass or less of the organic powder per 100 parts by mass of the biodegradable resin. (B) The average peripheral speed of the rotary blades is 8 m / sec to 20 m / sec, and the mixing time is 7 minutes or more and 60 minutes or less. (C) The melting point T°C of the biodegradable resin is 50°C or higher and 140°C or lower, and the temperature inside the high-speed mixer is (T-20)°C or lower at the start of high-speed mixing and rises therefrom to a temperature of (T+15)°C or higher at the end of high-speed mixing.

[0010] In the compounding step, the temperature inside the machine may be increased by frictional heat generated by the rotation of the rotary blades.

[0011] The organic powder may have an average particle size of 10 μm to 50 μm.

[0012] A biodegradable resin composition may be produced by carrying out a kneading step in which the composite powder obtained by the above production method is kneaded with a biodegradable resin.

[0013] Alternatively, a biodegradable resin film may be produced by carrying out a molding step in which the biodegradable resin composition obtained by the above-mentioned production method is blown into an inflation molding solution at a blow ratio in the range of 3.0 to 5.0.

[0014] Furthermore, a biodegradable resin bag may be manufactured by carrying out a bag-making process in which a cylindrical body made of a biodegradable resin film obtained by the above manufacturing method is heat-sealed in the width direction of the cylindrical body and then cut. [Effects of the Invention]

[0015] According to the above-mentioned embodiment, a composite powder of a biodegradable resin and an organic powder can be obtained, which can suppress the generation of aggregates. By kneading the obtained composite powder with a biodegradable resin, a biodegradable resin composition can be obtained in which the organic powder is well dispersed in the biodegradable resin while suppressing the generation of aggregates. DETAILED DESCRIPTION OF THE INVENTION

[0016] [Method of manufacturing composite powder] The method for producing a composite powder of the present invention includes a compounding step of obtaining a composite powder by placing a biodegradable resin and an organic powder made of natural fibers in a high-speed mixer having rotating blades and mixing them at high speed, and the compounding step is carried out so as to satisfy all of the following conditions (A) to (C): (A) The ratio of the biodegradable resin and the organic powder to be charged into the high-speed mixer is 65 parts by mass or more and 900 parts by mass or less of the organic powder per 100 parts by mass of the biodegradable resin. (B) The mixing conditions of the high-speed mixer are that the average peripheral speed of the rotary blades is 8 m / sec to 20 m / sec, and the mixing time is 7 minutes or more and 60 minutes or less. (C) The melting point T°C of the biodegradable resin is 50°C or higher and 140°C or lower, and the temperature inside the high-speed mixer is (T-20)°C or lower at the start of high-speed mixing and rises therefrom to a temperature of (T+15)°C or higher at the end of high-speed mixing.

[0017] In the compounding process, a high-speed mixer with rotating blades is used to compound organic powders made from biodegradable resin and natural fibers. Examples of high-speed mixers that can be used include a Henschel mixer manufactured by Nippon Coke & Engineering Co., Ltd. and a Super Mixer manufactured by Kawata Corporation. The rotating blades of a high-speed mixer typically consist of two blades: a lower blade and an upper blade. This configuration allows the lower blade to convect the raw material (processing material) fed into the high-speed mixer in an up-and-down direction, while the upper blade applies a strong shear force to the convected raw material. There is no limit to the number of rotating blades; a three-blade configuration, consisting of a lower blade, an upper blade, and a middle blade, can be used, or a single blade that combines the functions of both the lower and upper blades can be used.

[0018] To prevent the composite powder from becoming lumpy due to excess biodegradable resin, the ratio of the biodegradable resin and organic powder to be added to the high-speed mixer should be 65 parts by mass or more, preferably 80 parts by mass or more, and more preferably 100 parts by mass or more, of the organic powder per 100 parts by mass of biodegradable resin. To adequately coat the surface of the organic powder with biodegradable resin, the ratio of the organic powder to 100 parts by mass of biodegradable resin should be 900 parts by mass or less, preferably 700 parts by mass or less, and more preferably 500 parts by mass or less. By keeping the ratio within the above range, it is possible to prevent any uncomposite biodegradable resin or organic powder from remaining.

[0019] That is, in the compounding step, by feeding the biodegradable resin and the organic powder into the high-speed mixer in the above-mentioned ratio, the surface of the organic powder is adequately coated with the biodegradable resin. Therefore, when the biodegradable resin and the composite powder are mixed in the subsequent kneading step, a biodegradable resin composition can be obtained in which the composite powder (and hence the organic powder) is well dispersed in the biodegradable resin.

[0020] On the other hand, if the amount of organic powder relative to the biodegradable resin exceeds the above-mentioned ratio range, the amount of biodegradable resin covering the surface of the organic powder will be insufficient. As a result, there is a high possibility that agglomerates of the organic powder will occur in the biodegradable resin during the kneading process. Also, if the amount of organic powder relative to the biodegradable resin is small and falls below the above-mentioned ratio range, there will be an excess of biodegradable resin, causing some of the composite powder to become lumpy, which may hinder the dispersion of the organic powder in the biodegradable resin during the subsequent kneading process.

[0021] The average peripheral speed of the rotating blades should be 8 m / s or more, preferably 12 m / s or more, so that shear force acts on the biodegradable resin and organic powder fed into the high-speed mixer to compound them in a finely divided state. Furthermore, to prevent the raw materials from being deteriorated due to localized temperature increases caused by frictional heat, the average peripheral speed of the rotating blades should be 20 m / s or less, preferably 19 m / s or less.

[0022] The temperature inside the high-speed mixer at the start of high-speed mixing should be room temperature (approximately 10°C to 30°C). Here, the temperature inside the mixer refers to the temperature measured by a temperature sensor located near the rotating blades inside the high-speed mixer. Since the mixture is constantly in contact with the temperature sensor during high-speed mixing, the temperature inside the mixer = the mixture temperature. When high-speed mixing starts, the temperature inside the high-speed mixer is preferably (T-20)°C or lower, where T°C is the melting point of the biodegradable resin. This allows for uniform compounding to proceed.

[0023] During high-speed mixing, the temperature inside the machine continues to rise from the temperature at the start of high-speed mixing until the temperature inside the machine reaches (T + 15)°C or higher at the end of high-speed mixing. This allows the biodegradable resin and organic powder to be composited without any unmelted biodegradable resin remaining. Note that the temperature at the end of high-speed mixing must be low enough to prevent the biodegradable resin and organic powder from deteriorating.

[0024] The mixing time using the high-speed mixer should be 7 minutes or more, preferably 10 minutes or more, so that the biodegradable resin and organic powder fed into the high-speed mixer are uniformly composited. However, since the properties of the composite powder obtained do not change significantly even if the mixing time is extended, it is preferable to set the mixing time to 60 minutes or less, more preferably 50 minutes or less.

[0025] During high-speed mixing, the temperature inside the mixer can be increased by a heating means, or by the frictional heat generated between the mixture and the rotating blades inside the mixer. In this case, the total amount of the biodegradable resin and organic powder charged should be 200 g or more, preferably 300 g or more, per 1 L of the mixer's internal volume to generate sufficient frictional heat for heating. Furthermore, to thoroughly mix the biodegradable resin and organic powder, the total amount of the biodegradable resin and organic powder charged should be 400 g or less, preferably 350 g or less, per 1 L of the mixer's internal volume.

[0026] The biodegradable resin used in the present invention is not particularly limited in type as long as it is a thermoplastic resin, but it is preferable to use a polyester-based resin with excellent biodegradability. Examples of biodegradable polyester-based resins include polyhydroxyalkanoates such as 3-hydroxybutyrate (PHB) and poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV), aliphatic polyester-based resins, and aliphatic aromatic polyester-based resins. However, it is preferable to use an aliphatic polyester-based resin from the viewpoint of the balance between moldability and biodegradability.

[0027] Aliphatic polyester resins can be obtained, for example, by condensation polymerization of an aliphatic dicarboxylic acid and an aliphatic diol. The aliphatic dicarboxylic acid is preferably an alkylene dicarboxylic acid having 2 to 8 carbon atoms, and specific examples thereof include oxalic acid, malonic acid, succinic acid, glutaric acid, adipic acid, pimelic acid, and suberic acid. The aliphatic diol is preferably an alkylene glycol having 2 to 4 carbon atoms, and specific examples thereof include ethylene glycol, 1,3-propylene glycol, and 1,4-butanediol. Specific examples of aliphatic polyesters obtained by condensation polymerization of an aliphatic dicarboxylic acid and an aliphatic diol include polybutylene succinate (PBS) and polybutylene succinate adipate (PBSA). Polycaprolactone obtained by ring-opening polymerization of ε-caprolactone can also be used.

[0028] Among the polyester resins, PBSA is obtained by copolymerizing 1,4-butanediol with succinic acid and adipic acid. PBSA contains repeating units derived from 1,4-butanediol and two types of dicarboxylic acid units: repeating units derived from succinic acid (succinic acid units) and repeating units derived from adipic acid (adipic acid units). The adipic acid units may account for 5 mol% or more, preferably 10 mol% or more, and more preferably 15 mol% or more of the total dicarboxylic acid units. The adipic acid units may account for 5 mol% or less, preferably 45 mol% or less, and more preferably 40 mol% or less. By adjusting the content within the above range, the crystallinity of the resin can be reduced, thereby increasing the biodegradation rate.

[0029] PHBV is a copolymer of 3-hydroxybutyric acid and 3-hydroxyvaleric acid. PHBV contains repeating units derived from 3-hydroxybutyric acid (hydroxybutyric acid units) and repeating units derived from 3-hydroxyvaleric acid (hydroxyvaleric acid units). Of all repeating units of PHBV, the hydroxybutyric acid units preferably account for 80.0 mol% or more, more preferably 85.0 mol% or more, and preferably 99.8 mol% or less. By keeping the hydroxybutyric acid units within the above range, the productivity and flexibility of PHBV tend to be improved.

[0030] Aliphatic aromatic polyester resins can be obtained, for example, by polycondensation of an aliphatic dicarboxylic acid, an aromatic dicarboxylic acid, and an aliphatic diol. Examples of aromatic dicarboxylic acids include terephthalic acid and isophthalic acid. The aliphatic dicarboxylic acids and aliphatic diols that can be used are the same as those described as raw materials for aliphatic polyester resins. Specific examples of aliphatic aromatic polyesters include polybutylene adipate terephthalate (PBAT), polybutylene sebacate terephthalate, polybutylene azelate terephthalate, and polybutylene succinate terephthalate.

[0031] The melting point (T) °C of the biodegradable resin is preferably 50 °C or higher, more preferably 60 °C or higher, in order to prevent clumping due to melting of the composite powders. Furthermore, the melting point (T) °C of the biodegradable resin is preferably 140 °C or lower, more preferably 130 °C or lower, in order to smoothly perform the composite while preventing deterioration of the organic powder. When there are multiple melting points, it is preferable that at least one of the melting points is within the above range.

[0032] The naturally occurring organic powder may be any one that is biodegradable. Specific examples include cellulose-based powders such as wood flour, pulp powder, and cellulose powder, as well as finely divided powders of plant fibers such as cotton, silk, and hemp, and starch. Among these, cellulose powder is preferred. The average particle size of the organic powder is not particularly limited, but from the perspective of ease of handling and dispersibility in resin, it should be 10 μm or more, preferably 15 μm or more. It should also be 50 μm or less, preferably 40 μm or less. Furthermore, if the average particle size of the organic powder is within the above range, frictional heat generated by the rotation of the rotating blades during the compounding process is more likely to be generated, allowing for a smoother temperature rise inside the machine. The average particle size here refers to the 50% average particle size (median diameter d50) of the cumulative distribution on a volume basis, and can be measured by laser diffraction / scattering.

[0033] The raw material composition introduced into the high-speed mixer may contain a biodegradable resin and organic powder, as well as a dispersant to improve the affinity and dispersibility between the biodegradable resin and the organic powder. Examples of dispersants include higher fatty acids having 10 to 22 carbon atoms, such as oleic acid, stearic acid, erucic acid, palmitic acid, lauric acid, and behenic acid, and their metal salts. Among these, alkali metal stearates, such as calcium stearate and magnesium stearate, are preferred. The amount of dispersant added is preferably 0.2 parts by mass or more, more preferably 0.5 parts by mass or more, and preferably 3.0 parts by mass or less, more preferably 2.0 parts by mass or less, per 100 parts by mass of the biodegradable resin.

[0034] [Method for producing biodegradable resin composition] The composite powder obtained by carrying out the above-mentioned compounding step can suppress the generation of agglomerates of the organic powder and has excellent fluidity. Therefore, by carrying out a kneading step in which the composite powder is used as a master batch and is kneaded with a biodegradable resin, a biodegradable resin composition in which the organic powder is well dispersed in the biodegradable resin can be obtained.

[0035] The biodegradable resin composition contains at least a biodegradable resin and a composite powder. The biodegradable resin kneaded with the composite powder in the kneading step can be the same resin as the biodegradable resin contained in the composite powder. Furthermore, as the biodegradable resin used in the kneading step, in addition to the biodegradable resin contained in the composite powder, a different type of biodegradable resin can also be used in combination. The biodegradable resins that can be used are as explained in the section on the manufacturing method of the composite powder.

[0036] When multiple types of biodegradable resins are used in the biodegradable resin composition, one of them is composited with the organic powder in the composite process. The resin to be used in the composite process among the multiple biodegradable resins can be the resin that is the main component of the biodegradable resin composition, preferably a resin that accounts for 50% by mass or more of the total biodegradable resins. It is also possible to select a biodegradable resin whose melting point is in the range of 50°C to 140°C, which is a temperature range suitable for the composite process.

[0037] In the kneading process, the biodegradable resin constituting the composite powder is uniformly mixed with the biodegradable resin blended in the kneading process, and the organic powder in the biodegradable resin composition is uniformly dispersed in the biodegradable resin. From the viewpoint of improving biodegradability, the content of the organic powder in the biodegradable resin composition may be 1.0% by mass or more, preferably 1.5% by mass or more, and more preferably 2.0% by mass or more. From the viewpoint of film-forming properties, the content of the organic powder in the biodegradable resin composition may be 25.0% by mass or less, preferably 20.0% by mass or less, and more preferably 15.0% by mass or less. The blending ratio of the biodegradable resin and the composite powder in the kneading process may be adjusted appropriately, taking into account the content of the organic powder in the composite powder, so that the final content of the organic powder in the biodegradable resin composition falls within the above-mentioned range.

[0038] From the viewpoint of moldability (film-forming ability), the biodegradable resin used in the biodegradable resin composition can be an aliphatic polyester resin obtained by condensation polymerization of an aliphatic dicarboxylic acid and an aliphatic diol, such as PBS or PBSA. Alternatively, the biodegradability of the biodegradable resin composition can be improved by using an aliphatic polyester resin as the main component and a different biodegradable resin, such as PCL or polyhydroxyalkanoic acid. In this case, from the viewpoint of improving biodegradability, the content of the different biodegradable resin relative to the total biodegradable resin should be 2.0% by mass or more, preferably 4.0% by mass or more, and more preferably 8.0% by mass or more. From the viewpoint of maintaining moldability (film-forming ability), the content should be 25.0% by mass or less, preferably 20.0% by mass or less, and more preferably 15.0% by mass or less.

[0039] The biodegradable resin composition may contain, as needed, commonly used additives such as fillers, colorants, lubricants, antistatic agents, ultraviolet absorbers, plasticizers, stabilizers such as antioxidants, colorants such as dyes and pigments, slip agents, and antiblocking agents, provided that the object of the present invention is not impaired.

[0040] Examples of kneaders used in the kneading step include roll-type kneaders such as roll mills, Banbury mixers, and continuous kneaders such as twin-screw extruders. The biodegradable resin composition after the kneading step is used as a pellet-shaped or powdered molding raw material. As the kneader, it is preferable to use a twin-screw extruder, as this allows for the continuous production of a highly kneaded biodegradable resin composition.

[0041] [Method for manufacturing biodegradable resin film] The biodegradable resin composition obtained by the above-mentioned kneading step can be molded by a molding method such as extrusion molding, inflation molding, injection molding, etc. In particular, molding into a film or sheet by inflation molding or T-die extrusion molding is preferred because the effects of the present invention are significantly exhibited.

[0042] That is, the biodegradable resin composition obtained by the present invention has a low content of aggregates. Therefore, when the biodegradable resin composition is extruded from an extruder, the aggregates can be accurately removed by passing it through a filter. Furthermore, the biodegradable resin composition of the present invention is less likely to clog even when continuously extruded from an extruder, making it possible to mold the biodegradable resin composition continuously for a long period of time. Furthermore, by removing aggregates from a molded product molded into a film or sheet, it becomes possible to maintain good commercial value and mechanical properties.

[0043] The mesh size of the filter used in the extruder is preferably 10 mesh or more and 80 mesh or less from the viewpoint of accurately removing agglomerates and suppressing clogging and pressure increases, and the accuracy of agglomerate removal can be improved by stacking multiple filters.

[0044] In particular, the biodegradable resin composition obtained by the kneading step described above can be subjected to a blow molding step in which the composition is blown into an inflation molding solution at a blow ratio in the range of 3.0 to 5.0 to obtain a biodegradable resin film with excellent mechanical strength. From the viewpoint of mechanical strength, the blow ratio during inflation molding is preferably 3.0 or more, more preferably 4.0 or more. Furthermore, from the viewpoint of film formation, the blow ratio is preferably 5.0 or less, more preferably 4.5 or less. Here, the blow ratio refers to the ratio R2 / R1, where R1 is the radius of the annular die and R2 is the final radius of the cylindrical body after film formation.

[0045] [Manufacturing method for biodegradable resin bags] The biodegradable resin film obtained by carrying out the above-mentioned molding process is formed into a cylindrical shape. This cylindrical body can be cut open and used as a film. Alternatively, a biodegradable resin bag can be manufactured by carrying out a bag-making process in which the cylindrical body is heat-sealed in the width direction and cut. The biodegradable resin bag obtained in this manner has good mechanical strength and, since it contains organic powder, has excellent biodegradability.

[0046] The uses of the biodegradable resin molded articles obtained by the present invention are not particularly limited, and they can be used, for example, as films or sheets for packaging applications such as plastic bags and exterior packaging films, or laminates of these films or sheets with paper, or bags or containers made from these, as well as components for sanitary products, agricultural and horticultural materials, and civil engineering and construction materials. Examples of sanitary products include disposable paper diapers, incontinence pads, and sanitary napkins. Examples of agricultural and horticultural materials include mulch film, seedling pots, gardening tape, fruit cultivation bags, stakes, fumigation sheets, and greenhouse films. Examples of civil engineering and construction materials include vegetation nets, vegetation pots, three-dimensional netting, civil engineering fibers, stakes, and heat insulating materials. [Example]

[0047] The present invention will be described in more detail below using examples, but the present invention is not limited to these examples as long as it does not deviate from the gist of the invention. In this example, cellulose powder was used as the organic powder, and a composite powder was produced by a compounding process. The obtained composite powder was kneaded with a biodegradable resin (by carrying out the kneading process) to produce a biodegradable resin composition. The obtained biodegradable resin composition was blown into a film (by carrying out the molding process) to produce a biodegradable resin film. The details of each process will be explained below.

[0048] [Combining process] The high-speed mixer used was the FM5C / 1 manufactured by Nippon Coke & Engineering Co., Ltd. (capacity: 5 L). The rotating blades consisted of two blades: a lower blade and an upper blade (diameter of the rotating blades: both lower and upper blades were 75 mm). The biodegradable resin, organic powder, and dispersant shown below were fed into this high-speed rotating machine to carry out the compounding process. <Biodegradable resin> Polybutylene succinate adipate (PBSA): FD92PM manufactured by PTTMCC Biochem, melting point: 85°C, adipic acid units relative to total dicarboxylic acid units: 27.0 mol% <Organic powder> Cellulose powder (CP): Nippon Paper Industries KC Flock W-400, volume-based cumulative distribution 50% average particle size 24 μm <Dispersant> Magnesium stearate (StMg)

[0049] In this example, heating was not performed using a heating means, but was performed using frictional heat generated during high-speed mixing. The temperature inside the machine was room temperature (25°C) when high-speed mixing began, but eventually rose to the temperature (final temperature inside the machine) shown in Table 1. The compounding conditions and the state of the composite powder after compounding are shown in Table 1.

[0050] [Table 1]

[0051] [Kneading process] A kneading process was carried out using the composite powder No. 1-2 obtained in the above-mentioned compounding process. Specifically, as shown in Table 2, a biodegradable resin was added to the composite powder to adjust the biodegradable resin and cellulose powder to a predetermined blend ratio, and the mixture was extruded into strands using a twin-screw extruder with a screw diameter of 29 mm at a compounding temperature of 150°C, and pelletized biodegradable resin compositions were produced using a pelletizer (No. 2-3 to No. 2-9). In this process, the following resins were used as biodegradable resins in addition to the PBSA used in the compounding process. Polycaprolactone (PCL): Daicel Corporation's Plaxel H8C, melting point: 60°C, average molecular weight: 80,000 Poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV): Y1000P from Cheonan Biomaterials, melting point: 166°C, hydroxybutyric acid units relative to total repeating units: 99.4 mol%

[0052] The percentages for each component in Table 2 indicate the mass % of the biodegradable resin composition. In this step, 1.5 mass % magnesium stearate was added as a dispersant. In Table 2, Nos. 2-3 to 2-9, in which CP was blended in the form of a composite powder, were blended with the composite powder having a composition of 50 mass % PBSA and 50 mass % CP. As an example, No. 2-5 was blended with 78.5 mass % PBSA, 10.0 mass % composite powder, 10.0 mass % PCL, and 1.5 mass % magnesium stearate, resulting in a composition of 83.5 mass % PBSA, 5.0 mass % CP, 10.0 mass % PCL, and 1.5 mass % magnesium stearate. For comparative materials No. 2-1 and No. 2-2, the biodegradable resin and cellulose powder were directly kneaded in a twin-screw extruder without using the composite powder.

[0053] [Table 2]

[0054] [Molding process] Biodegradable resin films were produced using an inflation molding machine using the biodegradable resin compositions shown in Table 2. A 60-mesh filter was placed inside the extruder of the inflation molding machine, and the resin compositions that passed through the filter were inflation-molded using a 70-mm diameter round die (molding temperature: 150°C) to produce 30-μm-thick cylindrical bodies. Table 2 shows the state of the residue on the filter after molding 5 kg of each sample, as well as the blow ratio and film-forming properties.

[0055] [Evaluation of biodegradable films] The biodegradable resin films prepared from the samples in Table 2 were evaluated. The evaluation methods were as follows.

[0056] (1)Tear strength The tear strength was measured in accordance with JIS K7128-2. Specifically, an Elmendorf testing machine was used. Tests were conducted with n=5, and the average value was used. Note that tear strength is particularly important in the machine direction (MD). Therefore, measurements were conducted in the MD direction in this test.

[0057] (2) Film Impact A test piece cut to 100 mm x 100 mm was attached to a film impact tester manufactured by Toyo Seiki Seisakusho, and the force required to break through the film was measured and taken as the film impact. Measurements were made five times, and the average value was used.

[0058] (3) BOD decomposition test According to ASTM D6691-17, the BOD biodegradability of the film samples in seawater after 120 days was measured using a BOD tester OxiTop (manufactured by WTW Co., Ltd.) The seawater used was collected from Kawanoe Port in Shikokuchuo City.

[0059] (4) Weight loss measurement A laboratory-scale marine environment was recreated in a tank (29 x 29 x 55 cm) by adding potassium dihydrogen phosphate (0.1 g / L) and ammonium chloride (0.5 g / L) to seawater collected from Kawanoe Port in Shikokuchuo City. The specimens were placed in a polyethylene mesh #24 case (opening: 924 μm, aperture ratio: 53%) and allowed to stand in seawater. After 12 weeks, the case was removed from the seawater to recover the specimens, which were then washed with methanol and ultrapure water. After drying, the specimens were weighed, and the weight loss was calculated by subtracting the weight from the initial weight.

[0060] [Evaluation results] Table 1 shows that the temperature inside the high-speed mixer increases as the amount of PBSA and CP charged increases. The melting point of PBSA is 85°C, and when heated 8°C higher than the melting point of the biodegradable resin (No. 1-1), some unmelted PBSA remained. In contrast, when heated 15°C higher than the melting point of the biodegradable resin (No. 1-3), a uniform composite was achieved. Furthermore, the temperature rise rate of No. 1-3, which contained a dispersant, was significantly faster than that of No. 1-2, which did not contain a dispersant. This is thought to be due to the increased dispersibility of the biodegradable resin and organic powder, which made frictional heat more likely to be generated.

[0061] From the above results, it can be seen that by setting the total amount of biodegradable resin and organic powder charged per 1 L of the high-speed mixer to 200 g or more, it becomes possible to heat the mixture to above 90°C, and by setting it to 300 g or more, it becomes possible to heat the mixture to above 100°C in a short period of time. Note that in this example, the results are shown for a PBSA:CP mass ratio of 50:50, but it has been confirmed that similar results are obtained for PBSA:CP mass ratios in the range of 60:40 to 10:90.

[0062] Table 2 shows that when organic powders were directly mixed with biodegradable resins without compounding, the filter placed in the extruder clogged within a short period of time, making long-term molding difficult. Furthermore, film formation became impossible as the organic powder content increased (Nos. 2-1 to 2-2). In contrast, when organic powders were pre-compounded and mixed with biodegradable resins (Nos. 2-3 to 2-9), filter residue was minimal, long-term film formation was possible, and the resulting films did not contain problematic aggregates. Furthermore, when PBSA was used in combination with other biodegradable resins (Nos. 2-5 and 2-8), the residue on the filter and film formation were evaluated to be equivalent to those of Nos. 2-3 to 2-4, which used PBSA alone.

[0063] To evaluate the BOD biodegradability and weight loss rate, tests were conducted on five samples: No. 2-1, No. 2-3, and No. 2-4, which used PBSA alone as the biodegradable resin; No. 2-5, which used a combination of PBSA and PCL; and No. 2-8, which used a combination of PBSA and PHBV. For comparison, No. 2-10, a 30 μm-thick 100% PBSA film, and No. 2-11, a 100% cellulose filter paper (FILTER PAPER CHROMATOGRAPHY ITEM 50, manufactured by Advantec), were used. The BOD biodegradability results for each sample were expressed as an index, with the BOD biodegradability of No. 2-11, which is 100% cellulose, being set at 100 (see Table 2). Values closer to 100 indicate a biodegradability equivalent to that of cellulose.

[0064] As shown in Table 2, No. 2-10, which was made with 100% PBSA, showed almost no biodegradation, whereas No. 2-3 to No. 2-5 and No. 2-8, which contained PBSA in the form of a composite powder, showed significantly improved BOD biodegradability and weight loss. This was thought to be due to the effect of CP dispersed in the PBSA. Comparing No. 2-3, which used PBSA alone as the biodegradable resin, with No. 2-5 and No. 2-8, which used PBSA in combination with other biodegradable resins, the latter tended to be more biodegradable. In particular, No. 2-5, which used PBSA in combination with PCL as the biodegradable resin, showed biodegradability similar to that of No. 2-11, a 100% cellulose filter paper.

[0065] In contrast, No. 2-1, in which CP was directly mixed with PBSA without being compounded, showed a significantly lower BOD biodegradability than No. 2-3. This is thought to be because the CP was not uniformly dispersed in the PBSA, resulting in the presence of aggregates, which caused the biodegradation of the film to proceed unevenly. No. 2-1 also showed a high weight loss of 99.6%, which is presumed to be due to the film's uneven biodegradation, resulting in pieces smaller than the mesh openings that make up the case, which then fell off. This result also shows that No. 2-5 has excellent biodegradability.

[0066] Next, we examined the mechanical properties (MD tear strength and film impact) of the film after molding. For example, the target values for MD tear strength and film impact required for use in plastic bags are approximately 40 mN and 0.3 J, respectively. Regarding MD tear strength, No. 2-1 and 2-3 to 2-9 all achieved 40 mN or higher. Conversely, regarding film impact, films using PBSA in combination with other biodegradable resins (No. 2-5 and No. 2-8) tended to have lower film impact than No. 2-3, which used PBSA alone as the biodegradable resin. However, for both No. 2-5 and No. 2-8, film impact was significantly improved by increasing the blow ratio above 2.7 (No. 2-6, No. 2-7, and No. 2-9). In particular, No. 2-6 and No. 2-7, which used a combination of PBSA and PCL, achieved film impact levels practical for use in plastic bags.

[0067] Although No. 2-9, which uses a combination of PBSA and PHBV, does not reach the levels of No. 2-6 in terms of both MD tear strength and film impact, it is believed to be sufficiently usable for other applications (e.g., packaging film applications) that do not require the same level of performance as plastic bags. Thus, by adjusting the blow ratio depending on the biodegradable resin used, it is possible to produce a film suited to the application. As mentioned above, the reason why films can be produced at a high blow ratio even when an organic powder is contained is thought to be because the biodegradable resin composition is produced using a composite powder, which suppresses the generation of aggregates that cause film breakage during film production.

[0068] Although the embodiments of the present invention have been described above, the scope of the present invention is not limited to these, and various modifications can be made without departing from the spirit of the invention.

Claims

1. The method includes a compounding step of mixing a biodegradable resin and a naturally-derived organic powder at high speed in a high-speed mixer having a rotary blade to obtain a composite powder, A method for producing a composite powder, the compounding step being carried out so as to satisfy all of the following conditions (A) to (C): (A) The ratio of the biodegradable resin and the organic powder to be fed into the high-speed mixer is 65 parts by mass or more and 900 parts by mass or less of the organic powder per 100 parts by mass of the biodegradable resin. (B) The average peripheral speed of the rotary blades is 8 m / sec to 20 m / sec, and the mixing time is 7 minutes or more and 60 minutes or less. (C) The melting point T°C of the biodegradable resin is 50°C or higher and 140°C or lower, and the temperature inside the high-speed mixer is (T-20)°C or lower at the start of high-speed mixing and rises therefrom to a temperature of (T+15)°C or higher at the end of high-speed mixing.

2. 2. The method for producing a composite powder according to claim 1, wherein the temperature inside the machine is increased by frictional heat generated by the rotation of the rotary blades in the compounding step.

3. 2. The method for producing a composite powder according to claim 1, wherein the organic powder has an average particle size of 10 μm to 50 μm.

4. A method for producing a biodegradable resin composition, comprising a kneading step of kneading the composite powder obtained by the method according to any one of claims 1 to 3 with a biodegradable resin.

5. A method for producing a biodegradable resin film, comprising a molding step of inflation-molding the biodegradable resin composition obtained by the manufacturing method according to claim 4 at a blow ratio in the range of 3.0 to 5.

0.

6. A method for producing a biodegradable resin bag, comprising a bag-making step of heat-sealing a cylindrical body made of a biodegradable resin film obtained by the method according to claim 5 in the width direction of the cylindrical body and cutting the cylindrical body.

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