Method for producing biodegradable resin particles and method for producing biodegradable resin foam particles

Abstract

To obtain a biodegradable resin particle that are highly productive and not mutually adhered.SOLUTION: A manufacturing method of the present invention includes a crushing process of unraveling a mutually adhered resin particle (1) by an impact of a rotating knife to obtain an unraveled resin particle (2). The crushing process includes passing the unraveled resin particles (2) through a cylindrical screen (20), and a rotation speed of the knife (10) is 500 to 5000 rpm and a gap of the cylindrical screen (20) is greater than a length of one unraveled resin particle (2) and less than the length of one unraveled resin particle (2)×3.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a method for producing biodegradable resin particles, biodegradable resin particles, and biodegradable resin foam particles.

Background Art

[0002] Petroleum-derived plastics are discarded in large quantities every year, and the shortage of landfill sites or environmental pollution caused by these large amounts of waste has been taken up as a serious problem. In recent years, microplastics have become a major problem in the marine environment. For this reason, biodegradable plastics that are decomposed by the action of microorganisms in the environment such as the sea and soil, landfill sites, or compost have attracted attention. Biodegradable plastics are being developed with the aim of wide application to materials for the agricultural, forestry, and fisheries industries used in the environment, food containers, packaging materials, sanitary products, garbage bags, etc. that are difficult to recover or reuse after use. Furthermore, foams composed of biodegradable plastics are expected to be used in packaging cushioning materials, agricultural boxes, fish boxes, automotive parts, building materials, civil engineering materials, etc.

[0003] In addition, technologies for using the above-mentioned biodegradable plastics as resin molded bodies have been studied. For example, Patent Document 1 discloses a polyester resin molded body in which fine particles of polyhydroxyalkanoate are attached to a part of the surface of a molded body of polyhydroxyalkanoate.

[0004] In addition, Patent Document 2 discloses an aliphatic polyester resin composition containing polyhydroxyalkanoate, a compound having an amide bond, and pentaerythritol.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0006] However, the prior art as described above has room for improvement in terms of increasing the productivity of biodegradable resin particles and obtaining non-agglomerated biodegradable resin particles.

[0007] In the technique described in Patent Document 1, when producing resin particles of polyhydroxyalkanoate, fine particles of polyhydroxyalkanoate adhere to a part of the surface of the resin particles. Thereby, blocking during the production of the resin particles can be prevented. However, in the technique described in Patent Document 1, fine particles of polyhydroxyalkanoate may fly during the production of the resin particles and during the subsequent processing of the resin particles, which may deteriorate the working environment. Further, it has been confirmed by the present inventor that, for example, it is difficult to produce small-sized pellets that are particularly suitable for the production of biodegradable resin foamed particles and have a high quality requirement level by the method described in Patent Document 1.

[0008] Also, in the technique described in Patent Document 2, by blending a compound having an amide bond and pentaerythritol with polyhydroxyalkanoate, the slowness of crystallization of polyhydroxyalkanoate is improved, and it is made excellent in molding processability and productivity. When the composition described in Patent Document 2 is extruded from a melt extruder through a die, it is possible to improve the strand linear velocity to the maximum level at which pelletization can be achieved. However, the obtained pellets may adhere to each other. It has been confirmed by the present inventor that when producing biodegradable resin foamed particles using the adhered pellets, the pellets frequently clog pipes and the like, and it is difficult to stably obtain the foamed particles.

[0009] One aspect of the present invention aims to realize a method for producing biodegradable resin particles, biodegradable resin particles, and biodegradable resin foamed particles that can increase the productivity of biodegradable resin particles and obtain non-agglomerated biodegradable resin particles.

Means for Solving the Problems

[0010] As a result of intensive research to solve the above problems, the inventors of the present invention have found that by crushing the adhered biodegradable resin particles produced by melt extrusion under specific conditions, the productivity of the biodegradable resin particles can be increased and non-adhered biodegradable resin particles can be obtained, thus completing the present invention.

[0011] That is, one aspect of the present invention includes the following configuration.

[0012] 〔1〕A granulation step of obtaining adhered biodegradable resin particles by extruding a melt-kneaded biodegradable resin composition through a die and cutting it into a predetermined size, and a crushing step of loosening the adhered biodegradable resin particles by the impact of a rotating knife to obtain loosened biodegradable resin particles, wherein the crushing step includes a sizing step of passing the loosened biodegradable resin particles through a cylindrical screen installed outside the knife, the rotational speed of the knife is 500 to 5000 rpm, and the mesh opening of the cylindrical screen is not less than the length of one of the loosened biodegradable resin particles and not more than three times the length of one of the loosened biodegradable resin particles. A method for producing biodegradable resin particles.

[0013] 〔2〕The method for producing biodegradable resin particles according to 〔1〕, wherein in the granulation step, the biodegradable resin composition discharged from the die is cooled and then cut into a predetermined size.

[0014] 〔3〕The method for producing biodegradable resin particles according to 〔1〕 or 〔2〕, wherein the loosened biodegradable resin particles have a weight of 0.3 to 10 mg per piece and a length / diameter ratio of 0.7 to 3.

[0015] 〔4〕The biodegradable resin is one or more selected from the group consisting of poly(3-hydroxyalkanoate), polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, polycaprolactone, modified starch, and modified cellulose, and is the method for producing biodegradable resin particles according to any one of 〔1〕to 〔3〕.

[0016] 〔5〕The biodegradable resin is poly(3-hydroxyalkanoate), and is the method for producing biodegradable resin particles according to any one of 〔1〕to 〔3〕.

[0017] 〔6〕The poly(3-hydroxyalkanoate) is one or more selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate), and is the method for producing biodegradable resin particles according to 〔5〕.

[0018] 〔7〕Biodegradable resin particles obtained by the method for producing biodegradable resin particles according to any one of 〔1〕to 〔6〕.

[0019] 〔8〕Biodegradable resin foam particles obtained by foaming the biodegradable resin particles according to 〔7〕.

Advantages of the Invention

[0020] According to one aspect of the present invention, the productivity of the biodegradable resin particles can be increased, and biodegradable resin particles that are not adhered to each other can be obtained.

Brief Description of the Drawings

[0021]

Figure 1

Figure 2

Embodiments for Carrying out the Invention

[0022] An embodiment of the present invention will be described in detail below. Unless otherwise specified in this specification, "A~B" representing a numerical range means "A or more and B or less". Also, all the documents described in this specification are incorporated herein by reference.

[0023] [1. Method for Producing Biodegradable Resin Particles, Biodegradable Resin Particles and Foamed Particles] The method for producing biodegradable resin particles according to an embodiment of the present invention includes a granulation step of extruding a melt-kneaded biodegradable resin composition through a die and cutting it into a predetermined size to obtain adhered biodegradable resin particles. And the method for producing biodegradable resin particles according to an embodiment of the present invention includes the following (a) to (d). (a) It includes a disintegration step of loosening the adhered biodegradable resin particles by the impact of a rotating knife to obtain loosened biodegradable resin particles. (b) The disintegration step includes a sizing step of passing the loosened biodegradable resin particles through a cylindrical screen installed outside the knife. (c) The rotational speed of the knife is 500 to 5000 rpm. (d) The mesh opening of the cylindrical screen is not less than the length of one of the loosened biodegradable resin particles and not more than three times the length of one of the loosened biodegradable resin particles.

[0024] Also, the biodegradable resin particles according to an embodiment of the present invention are obtained by the above production method. Further, the biodegradable resin foamed particles according to an embodiment of the present invention are obtained by foaming the biodegradable resin particles.

[0025] In this specification, the "biodegradable resin composition" may be referred to as the "resin composition", the "biodegradable resin particles" may be referred to as the "resin particles", the "adhered biodegradable resin particles" may be referred to as the "adhered resin particles", the "method for producing biodegradable resin particles" may be referred to as the "production method", and the "method for producing biodegradable resin particles according to an embodiment of the present invention" may be referred to as the "present production method". Further, the "biodegradable resin foamed particles" may be referred to as the "foamed particles".

[0026] Here, in order to produce biodegradable resin foamed particles, small pellet-shaped resin particles (several mg / grain) as raw materials are required. For example, when resin particles of a biodegradable resin are produced by melt extrusion, since the biodegradable resin crystallizes more slowly than general-purpose resins such as polyethylene, the adhesion of the resin particles of the biodegradable resin is likely to occur. Further, the greater the amount of the melt-kneaded product discharged from the die of the melt extruder, the greater the number of adhered resin particles of the biodegradable resin. Therefore, it is difficult to increase the amount of the melt-kneaded product discharged from the die of the melt extruder to improve the productivity of the resin particles. Note that the adhered resin particles of the biodegradable resin are not suitable for the production of biodegradable resin foamed particles.

[0027] According to the present production method, by having the configurations (a) to (d) above, the adhered resin particles can be easily loosened. Therefore, the production efficiency of resin particles of a quality that can be used for the production of foamed particles can be improved, and the productivity can be increased. Therefore, according to the present production method, the productivity of the biodegradable resin particles can be increased, and non-adhered biodegradable resin particles can be obtained.

[0028] Incidentally, the weight and size per particle of the loosened biodegradable resin particles obtained in the crushing step are not particularly limited. This production method is applicable to the production of resin particles other than small pellet-shaped resin particles suitable for the production of expanded particles. Preferably, this production method is applied to the production of small pellet-shaped resin particles suitable for the production of expanded particles. That is, in this production method, the loosened biodegradable resin particles preferably have a weight of 0.3 to 10 mg per particle and a length / diameter of 0.7 to 3.

[0029] (Biodegradable resin particles) The biodegradable resin composition used in this production method contains a biodegradable resin. The biodegradable resin used in this production method is not particularly limited as long as it has biodegradability. "Biodegradability" in this embodiment refers to the property of being decomposed into low-molecular compounds by microorganisms in nature. Specifically, the presence or absence of biodegradability can be determined based on tests suitable for each environment, such as ISO 14855 (compost) and ISO 14851 (activated sludge) under aerobic conditions, and ISO 14853 (aqueous phase) and ISO 15985 (solid phase) under anaerobic conditions. Also, the degradability by microorganisms in seawater can be evaluated by measuring the biochemical oxygen demand.

[0030] The biodegradable resin is preferably at least one selected from the group consisting of poly(3-hydroxyalkanoate), polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, polycaprolactone, modified starch, and modified cellulose.

[0031] In this production method, the biodegradable resin can be used alone or in combination of two or more.

[0032] ​Among these biodegradable resins, from the viewpoints of excellent biodegradability and carbon neutrality, it is more preferable that the biodegradable resin is poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as P3HA). P3HA is a polyhydroxyalkanoate containing, as an essential repeating unit, a 3-hydroxyalkanoic acid repeating unit represented by the general formula: [-CHR-CH2-CO-O-] (wherein R is an alkyl group represented by C n H 2n+1 and n is an integer of 1 or more and 15 or less). Among them, those containing the repeating unit in an amount of 50 mol% or more, more preferably 70 mol% or more, based on all monomer repeating units (100 mol%) are preferable.

[0033] More specifically, examples of P3HA include poly(3-hydroxybutyrate) (P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate) (P3HB3HV3HH), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (P3HB4HB), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), and the like.

[0034] Note that P3HA produced by microorganisms (microorganism-produced P3HA) is usually P3HA composed only of D-form (R-form) polyhydroxyalkanoic acid monomer units. Among microorganism-produced P3HAs, P3HB, P3HB3HV, P3HB3HV3HH, P3HB3HH, and P3HB4HB are preferable, and P3HB, P3HB3HV, P3HB3HH, and P3HB4HB are more preferable, from the viewpoint of easy industrial production.

[0035] When P3HA (especially, microbially produced P3HA) contains 3-hydroxybutyric acid (3HB) repeating units as essential monomer units, from the viewpoint of the balance between flexibility and strength, the monomer composition ratio is preferably 80 mol% to 99 mol%, more preferably 85 mol% to 97 mol% of 3-hydroxybutyric acid (3HB) repeating units in all repeating units (100 mol%). When the composition ratio of the 3HB repeating units is 80 mol% or more, the rigidity of P3HA is further improved, and the crystallinity does not become too low, and purification tends to be easy. On the other hand, when the composition ratio of the 3HB repeating units is 99 mol% or less, the flexibility tends to be further improved. The monomer composition ratio of P3HA can be measured by gas chromatography or the like (for example, see International Publication No. 2014 / 020838).

[0036] The microorganism for producing microbially produced P3HA is not particularly limited as long as it has the ability to produce P3HAs. For example, as a P3HB-producing bacterium, Bacillus megaterium discovered in 1925 was the first, and other natural microorganisms such as Cupriavidus necator (former classification: Alcaligenes eutrophus, Ralstonia eutropha), Alcaligenes latus, etc. are mentioned. It is known that P3HB accumulates in the cells of these microorganisms.

[0037] In addition, as production bacteria for copolymers of 3HB and other hydroxyalkanoates, Aeromonas caviae, which is a P3HB3HV and P3HB3HH production bacterium, Alcaligenes eutrophus, which is a P3HB4HB production bacterium, etc. are known. In particular, regarding P3HB3HH, in order to increase the productivity of P3HB3HH, Alcaligenes eutrophus AC32 strain (Alcaligenes eutrophus AC32, FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) into which genes of P3HA synthase group are introduced, etc. are more preferable, and microbial cells in which P3HB3HH is accumulated in the cells by culturing these microorganisms under appropriate conditions are used. In addition to the above, according to the P3HA to be produced, genetically modified microorganisms into which various P3HA synthesis-related genes are introduced may be used, or the culture conditions including the type of substrate may be optimized.

[0038] The molecular weight of P3HA is not particularly limited as long as it exhibits substantially sufficient physical properties for the intended use. The range of the weight average molecular weight of P3HA is preferably from 200,000 to 2,000,000, more preferably from 250,000 to 1,500,000, and still more preferably from 300,000 to 1,000,000. If the weight average molecular weight is less than 200,000, the decrease in mechanical strength becomes large, which is not preferable.

[0039] The method for measuring the weight average molecular weight can be determined as the molecular weight in terms of polystyrene using gel permeation chromatography (GPC) (Shodex GPC-101 manufactured by Showa Denko KK), using polystyrene gel (Shodex K-804 manufactured by Showa Denko KK) for the column, and chloroform as the mobile phase. At this time, the calibration curve is prepared using polystyrenes with weight average molecular weights of 31,400, 197,000, 668,000, and 1,920,000. As the column in the GPC, a column appropriate for measuring the above molecular weight may be used.

[0040] In this manufacturing method, P3HA can be used alone or in combination of two or more kinds.

[0041] In addition to the resin component containing a biodegradable resin, the resin composition may further contain an additive. As the additive, for example, a crystal nucleating agent, a bubble regulator, a lubricant, a plasticizer, an antistatic agent, a flame retardant, a conductive agent, a heat insulating agent, a crosslinking agent, an antioxidant, an ultraviolet absorber, a colorant, an inorganic filler, an organic filler, a hydrolysis inhibitor, a water-containing agent, etc. can be used according to the purpose. As the additive, an additive having biodegradability is particularly preferable.

[0042] Examples of the crystal nucleating agent include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, talc, etc. One of these crystal nucleating agents may be used alone, or two or more kinds may be mixed and used. Further, when two or more kinds of crystal nucleating agents are mixed and used, the mixing ratio may be appropriately adjusted according to the purpose.

[0043] The amount of the crystal nucleating agent used is not particularly limited. The amount of the crystal nucleating agent used is preferably 5.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 1.5 parts by weight or less with respect to 100 parts by weight of the biodegradable resin. The lower limit of the amount of the crystal nucleating agent used with respect to the biodegradable resin is not particularly limited, but can be, for example, 0.1 part by weight or more with respect to 100 parts by weight of the biodegradable resin.

[0044] Examples of the bubble regulator include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, bentonite, etc. Among these bubble regulators, talc is preferable in terms of particularly excellent dispersibility in P3HA. Also, one of these bubble regulators may be used alone, or two or more kinds may be mixed and used. Further, when two or more kinds of bubble regulators are mixed and used, the mixing ratio may be appropriately adjusted according to the purpose.

[0045] The amount of the bubble regulator used is not particularly limited, but preferably 0.01 to 1.00 parts by weight, more preferably 0.03 to 0.50 parts by weight, and even more preferably 0.05 to 0.30 parts by weight with respect to 100 parts by weight of the biodegradable resin.

[0046] Examples of the lubricant include behenic acid amide, oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, N-stearyl behenic acid amide, N-stearyl erucic acid amide, ethylene bis stearic acid amide, ethylene bis oleic acid amide, ethylene bis erucic acid amide, ethylene bis lauric acid amide, ethylene bis capric acid amide, p-phenylene bis stearic acid amide, polycondensate of ethylenediamine, stearic acid and sebacic acid, and the like. Among these lubricants, behenic acid amide and / or erucic acid amide are preferable in that the lubricating effect on P3HA is particularly excellent. One type of these lubricants may be used alone, or two or more types may be mixed and used. Further, when two or more types of lubricants are mixed and used, the mixing ratio may be appropriately adjusted according to the purpose.

[0047] The amount of the lubricant used is not particularly limited, but preferably 0.01 to 5.00 parts by weight, more preferably 0.01 to 3.00 parts by weight, and even more preferably 0.01 to 1.50 parts by weight with respect to 100 parts by weight of the biodegradable resin. The amount of the lubricant used with respect to the biodegradable resin may be 0% with respect to 100 parts by weight of the biodegradable resin, that is, the resin composition may not contain a lubricant.

[0048] Examples of the plasticizer include glycerin ester compounds such as glycerin diacetomonolaurate, citrate ester compounds such as tributyl acetylcitrate, sebacic acid ester compounds such as dibutyl sebacate, adipic acid ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, isosorbide ester compounds, polycaprolactone compounds, dibasic acid ester compounds such as benzyl methyl diethylene glycol adipate, and the like. Among these, glycerin ester compounds, citrate ester compounds, sebacic acid ester compounds, and dibasic acid ester compounds are preferred in that they have particularly excellent plasticizing effects on P3HA. These plasticizers may be used alone or in combination of two or more. When two or more plasticizers are used in combination, the mixing ratio may be appropriately adjusted according to the purpose.

[0049] The amount of the plasticizer used is not particularly limited. For example, the amount of the plasticizer used is preferably 20 parts by weight or less, more preferably 15 parts by weight or less, still more preferably 10 parts by weight or less, and particularly preferably 5 parts by weight or less, based on 100 parts by weight of the biodegradable resin. The lower limit of the amount of the plasticizer used with respect to the biodegradable resin is not particularly limited, and may be, for example, 0%, that is, the resin composition may not contain a plasticizer.

[0050] The resin composition may contain a compound having an isocyanate group (hereinafter sometimes referred to as an isocyanate compound). However, the isocyanate compound may be toxic. Further, when the resin composition contains an isocyanate compound, the resulting foamed particles and foamed molded article may turn yellow.

[0051] Therefore, the amount of the isocyanate compound used is preferably less than 3.0 parts by weight, more preferably less than 1.0 part by weight, and still more preferably less than 0.1 part by weight, based on 100 parts by weight of the biodegradable resin. It is most preferable that the resin composition does not contain an isocyanate compound.

[0052] As the isocyanate compound, for example, a polyisocyanate compound having two or more isocyanate groups in one molecule can be used. Specific types of the isocyanate compound include aromatic isocyanate compounds, alicyclic isocyanate compounds, aliphatic isocyanate compounds, and the like. For example, (a) as the aromatic isocyanate compound, isocyanate compounds having a skeleton of tolylene, diphenylmethane, naphthylene, tolidine, xylene, and / or triphenylmethane can be mentioned; (b) as the alicyclic isocyanate compound, isocyanate compounds having a skeleton of isophorone and / or hydrogenated diphenylmethane can be mentioned; (c) as the aliphatic isocyanate compound, isocyanate compounds having a skeleton of hexamethylene and / or lysine can be mentioned. Furthermore, a mixture obtained by combining two or more of these isocyanate compounds can also be used. When using the isocyanate compound, it is preferable to use an isocyanate compound having a skeleton of tolylene and / or diphenylmethane, particularly an isocyanate compound (polyisocyanate) having a skeleton of diphenylmethane, from the viewpoints of versatility, handleability, weather resistance, etc.

[0053] The melt flow rate (MFR) of the biodegradable resin composition is not particularly limited as long as it exhibits substantially sufficient physical properties for the intended use. The range of the MFR of the biodegradable resin composition is preferably 1 to 20 g / 10 min, more preferably 1 to 17 g / 10 min, and even more preferably 1 to 15 g / 10 min. When the MFR is less than 1 g / 10 min, it tends to be difficult to obtain foamed particles with a low apparent density with only one foaming. On the other hand, when the MFR exceeds 20 g / 10 min, the closed cell ratio of the obtained foamed particles tends to be low.

[0054] The measurement method of the MFR of the biodegradable resin composition is determined by measuring with a melt flow index tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7210 at a load of 2.16 kg or 5 kg and a measurement temperature between 160 and 190 °C. The load and the measurement temperature may be appropriately determined according to the type and characteristics of the biodegradable resin.

[0055] (Granulation process) In the granulation process, the melt-kneaded biodegradable resin composition is extruded through a die and cut into a predetermined size to obtain mutually adherent biodegradable resin particles.

[0056] The method for obtaining the melt-kneaded product of the biodegradable resin composition is not particularly limited. Specific examples of the method include, for example, the following methods (a1) and (a2): (a1) A method in which a biodegradable resin and, if necessary, an additive are mixed or blended using a mixing device or the like to prepare a resin composition. Then, the resin composition is supplied to a melt-kneading device and melt-kneaded; (a2) A method in which a biodegradable resin and, if necessary, an additive are supplied to a melt-kneading device, and the resin composition is prepared (completed) in the melt-kneading device and the resin composition is melt-kneaded.

[0057] In the method of (a1), the order of mixing or blending (dry blending) the biodegradable resin and, if necessary, the additive is not particularly limited. In the method of (a2), the order of supplying the biodegradable resin and, if necessary, the additive to the melt-kneading device is not particularly limited.

[0058] In the method of (a1), the mixing device is not particularly limited, and examples include a ribbon blender, a flash blender, a tumbler mixer, a super mixer, and the like.

[0059] In the methods of (a1) and (a2), the melt-kneading device is not particularly limited, and examples include an extruder, a kneader, a Banbury mixer, and rolls. From the viewpoints of excellent productivity and convenience, an extruder is preferably used as the melt-kneading device, and a twin-screw extruder is more preferably used.

[0060] In addition, the temperature at which the resin composition is melt-kneaded cannot be generally specified because it depends on the type of biodegradable resin, physical properties (such as melting point, weight-average molecular weight, etc.), and the type of additives used. Regarding the temperature at which the resin composition is melt-kneaded, for example, the temperature of the melt-kneaded resin composition discharged from the nozzle of the die (hereinafter sometimes referred to as the composition temperature) is preferably 150°C to 200°C, more preferably 160°C to 195°C, and even more preferably 170°C to 190°C. When the composition temperature is 150°C or higher, there is no risk of insufficient melt-kneading of the resin composition. On the other hand, when the composition temperature is 200°C or lower, there is no risk of thermal decomposition of the biodegradable resin.

[0061] Also, the method of cutting the melt-kneaded resin composition is not particularly limited as long as the resin composition can be extruded from the die and cut into a predetermined size. By using a melt-kneading apparatus equipped with a die and a cutting apparatus as the melt-kneading apparatus, the resin composition can be easily formed into a desired shape. Specifically, the resin composition can be discharged from the nozzle of the die provided in the melt-kneading apparatus, and at the same time as the discharge or after the discharge, the resin composition can be cut by the cutting apparatus to form a desired shape. The shape of the obtained resin particles is not particularly limited, but cylindrical, elliptical cylindrical, spherical, cubic, rectangular parallelepiped, etc. are preferred because they are easy to use for foaming.

[0062] In the granulation step, the resin composition discharged from the nozzle of the die may be cooled. When cooling the resin composition discharged from the nozzle of the die, the resin composition may be cut by the cutting apparatus simultaneously with or after the cooling of the resin composition. In the granulation step, it is preferable to cut the biodegradable resin composition discharged from the die into a predetermined size after cooling the biodegradable resin composition.

[0063] When cooling the resin composition discharged from the die nozzle, the temperature shown by the cooled resin composition (hereinafter, may be referred to as the cooling temperature) cannot be generally specified because it depends on the type of biodegradable resin. However, from the viewpoint of crystallization of the melt-kneaded resin composition, the cooling temperature is preferably 10°C to 80°C, more preferably 20°C to 70°C, and even more preferably 30°C to 60°C.

[0064] In the granulation process, the melt-kneaded resin composition is extruded from the die nozzle in a strand shape. When the discharge amount of the resin composition is increased, blocking occurs between the strands during winding or between the resin particles after cutting. Here, blocking refers to the phenomenon where the strands adhere to each other (stick to each other) after being extruded from the die nozzle, or the cut pieces of the strands adhere to each other after the strands are cut by a cutting device. Therefore, in the granulation process, biodegradable resin particles that adhere to each other are obtained. These adhered biodegradable resin particles are not suitable for the production of foamed particles.

[0065] The ratio of the adhered biodegradable resin particles obtained in the granulation process is preferably 90% or less, more preferably 50% or less, and even more preferably 30% or less, based on all the biodegradable resin particles obtained in the granulation process.

[0066] As the discharge amount of the resin composition increases, the number of adhered resin particles increases. Therefore, in the production of conventional resin particles, it has been difficult to increase the discharge amount of the resin composition while reducing the number of adhered resin particles, and it has been difficult to improve the productivity of the resin particles.

[0067] In this production method, by performing a crushing process under specific conditions, the adhered resin particles can be easily loosened. Therefore, it is possible to increase the discharge amount of the resin composition while reducing the number of adhered resin particles. As a result, according to this production method, the yield efficiency of particularly small pellet-shaped resin particles is improved, and the productivity of the resin particles can be increased.

[0068] (Crushing process) In the crushing process, the agglomerated resin particles are loosened to obtain loosened biodegradable resin particles. FIG. 1 is a diagram schematically showing an example of a crusher used in the crushing process. In this manufacturing method, the crusher used in the crushing process is not limited to the configuration shown in FIG. 1.

[0069] As shown in FIG. 1, the crusher 100 includes a cylindrical crushing section 101 and a sizing section 102. At the upper part of the crushing section 101, an inlet 100a for the agglomerated resin particles 1 is provided. Also, at the lower part of the sizing section 102, an outlet 100b for the resin particles 2 loosened in the crushing section 101 is provided.

[0070] The crushing section 101 includes knives 10, a cylindrical screen 20, a shaft 30, and a bottom plate 40. The knives 10 rotate about the shaft 30. As shown in FIG. 2, the knives 10 include two blade portions 11 and 12. And, when viewed from the direction in which the shaft 30 extends, the blade portion 11 and the blade portion 12 are attached to the shaft 30 so as to be orthogonal to each other. By the collision of the agglomerated resin particles 1 and the rotating knives 10, the agglomerated resin particles 1 are loosened. The cylindrical screen 20 is mesh-shaped and has a plurality of holes. The cylindrical screen 20 constitutes the side surface of the cylindrical portion of the crushing section 101. Also, the bottom plate 40 constitutes the bottom surface of the cylindrical portion of the crushing section 101.

[0071] The sizing section 102 includes a cover 50 provided so as to cover the side surface of the cylindrical portion of the crushing section 101 while being separated therefrom. The sizing section 102 has a space formed by the cylindrical portion of the crushing section 101 and the cover 50. This space serves as a passage for the resin particles 2 to move toward the outlet 100b.

[0072] The crushing section 101 and the sizing section 102 communicate with each other via a mesh-like cylindrical screen 20, but do not communicate with each other via the bottom plate 40. Therefore, the resin particles 1 that are adhered to each other and have not been loosened in the crushing section 101 will accumulate on the bottom plate 40. On the other hand, the resin particles 2 that have been loosened in the crushing section 101 pass through the cylindrical screen 20 and reach the sizing section 102, or do not pass through the cylindrical screen 20 and accumulate on the bottom plate 40.

[0073] In this manufacturing method, the crushing process includes the sizing process. In the sizing process, the resin particles 1 that are adhered to each other are introduced from the inlet 100a of the crusher 100, and in the crushing section 101, the adhered resin particles 1 are loosened by the impact of the rotating knife 10 to obtain resin particles 2. Then, the resin particles 2 formed after loosening the adhered resin particles 1 are passed through a cylindrical screen 20 installed outside the knife 10. The adhered resin particles 1 that cannot be loosened by the impact of the knife 10 will accumulate on the bottom plate 40.

[0074] Here, the inventor of the present application earnestly studied various settings of the crusher 100 for the purpose of reducing the amount of the adhered resin particles 1 remaining inside the cylindrical screen 20 and on the bottom plate 40 in the crushing process including such a sizing process and obtaining good-quality resin particles 2 without adhesion. As a result, it was found that the above object can be achieved by setting the rotation speed of a specific knife 10 and setting the cylindrical screen 20 to a specific mesh size.

[0075] First, the rotation speed of the knife 10 is 500 - 5000 rpm, preferably 750 - 4500 rpm, more preferably 1000 - 4000 rpm. If the rotation speed of the knife 10 is 500 rpm or more, the adhered resin particles can be loosened to individual resin particles. Also, if the rotation speed of the knife 10 is 5000 rpm or less, the breakage of the resin particles can be suppressed.

[0076] Also, the mesh size of the cylindrical screen 20 is equal to or greater than the length of one resin particle 2 that has been loosened, and equal to or less than three times the length of one resin particle 2 that has been loosened, preferably equal to or less than two times the length of one resin particle 2 that has been loosened, and more preferably equal to or less than 1.5 times the length of one resin particle 2 that has been loosened. If the mesh size of the cylindrical screen 20 is less than the length of the resin particle 2, it becomes difficult for the resin particle 2 to move to the sizing section 102. On the other hand, if the mesh size of the cylindrical screen 20 exceeds three times the length of the resin particle 2, the resin particle 1 adhered to the resin particle 2 also moves to the sizing section 102 together with the resin particle 2.

[0077] The order in which the crushing step is performed is not particularly limited as long as it is after the granulation step. Specific examples of such an order include, for example, the methods (b1) and (b2) below: (b1) After the granulation step, all the adhered resin particles and the non - adhered resin particles are subjected to a crushing treatment.

[0078] (b2) After the granulation step, the adhered resin particles are separated from the non - adhered resin particles by a sieve, and then the adhered resin particles are subjected to a crushing treatment.

[0079] The proportion of fine products such as small resin particles or fine powder generated in the granulation step and the crushing step is preferably 10% or less, more preferably 5% or less, and even more preferably 3% or less, based on all the biodegradable resin particles obtained. The less the fine products are, the higher the productivity of the biodegradable resin particles.

[0080] After the crushing step, a sieve and a dust collector may be used to improve the uniformity of the resin particles used for manufacturing the foamed particles.

[0081] [3. Biodegradable Resin Particles] The resin particles loosened in the crushing step of the present invention preferably have a weight of 0.3 to 10 mg per particle and a length / diameter (ratio of length to diameter) of 0.7 to 3. Here, the length of the resin particle refers to the maximum value of the distance between two cut surfaces that appear (occur) on the resin particle when the resin particle is cut during the manufacturing process of the resin particle. Next, when the length direction of the resin particle is defined as the x direction, an arbitrary straight line y and a straight line z perpendicular to the straight line y are drawn on a cross-section (cross-section x) perpendicular to the x direction. The line segment obtained by cutting the straight line y on the cross-section x is defined as the line segment y, and the line segment obtained by cutting the straight line z on the cross-section x is defined as the line segment z. The diameter of the resin particle is intended to be the average value of the length of the line segment y and the length of the line segment z.

[0082] If the weight per resin particle is 0.3 mg or more, poor cutting of the strand in the granulation step can be reduced. On the other hand, if the weight per resin particle is 10.0 mg or less, the resin particles can be stably produced with high productivity. The weight per resin particle is preferably 0.5 to 7.5 mg, more preferably 0.7 to 5.0 mg.

[0083] Also, if the length / diameter of the resin particle is 0.7 or more, biodegradable foam particles with a good shape can be obtained. On the other hand, if the length / diameter of the resin particle is 3 or less, destruction of the resin particle in the crushing step can be suppressed. The length / diameter of the resin particle is preferably 0.8 to 2.7, more preferably 0.9 to 2.5.

[0084] The melting point of the resin particle (hereinafter sometimes referred to as "Tmp") is not particularly limited, but is preferably 50°C to 165°C, more preferably 60°C to 155°C.

[0085] Here, the melting point (Tmp) of the resin particles is measured by differential scanning calorimetry (hereinafter referred to as the "DSC method"). The specific operation procedure is as follows: (1) Weigh about 5 mg of the resin particles; (2) Raise the temperature of the resin particles from 10°C to 190°C at a heating rate of 10°C / min to melt the resin particles; (3) The temperature of the highest-temperature melting peak of the DSC curve of the resin particles obtained in the process of (2) above can be determined as the melting point of the resin particles.

[0086] [4. Biodegradable resin foamed particles] One embodiment of the present invention may include biodegradable resin foamed particles formed by foaming the above-described biodegradable resin particles (hereinafter, may also be simply referred to as "foamed particles"). The manufacturing method of the foamed particles according to this embodiment can adopt a conventionally known method as long as it can foam small pellet-shaped biodegradable resin particles.

[0087] The manufacturing method of the foamed particles according to this embodiment (a) A dispersion step of dispersing resin particles, an aqueous dispersion medium, a crosslinking agent, a foaming agent, and, if necessary, a dispersant, a crosslinking aid, a dispersion aid, and / or a plasticizer in a container; (b) A heating-pressure increasing step of raising the temperature inside the container to a constant temperature and increasing the pressure inside the container to a constant pressure; (c) A holding step of holding the temperature and pressure inside the container at a constant temperature and a constant pressure; (d) A discharging step of releasing one end of the container and discharging the dispersion liquid inside the container to a region (space) at a pressure lower than the foaming pressure (i.e., the pressure inside the container), is preferably included.

[0088] Examples of the manufacturing method of the foamed particles according to this embodiment include the methods described in International Publication No. WO2019 / 146555, International Publication No. WO2021 / 002092, etc.

Examples

[0089] Hereinafter, the present invention will be specifically described by way of examples, but the technical scope of the present invention is not limited by these examples.

[0090] 〔Materials〕 The substances used in the examples and comparative examples are shown below.

[0091] (Biodegradable resin) Biodegradable resin - 1: P3HB3HH (Kaneka biodegradable polymer PHBH X131N manufactured by Kaneka Corporation, monomer ratio is 3HB / 3HH = 95 / 5 (mol% / mol%)) Biodegradable resin - 2: Polybutylene succinate adipate (BioPBS FD92 manufactured by Mitsubishi Chemical Corporation) Biodegradable resin - 3: Polycaprolactone (Capa 6800 manufactured by Perstorp) (Bubble regulator) Talc (Talkan powder PK - S manufactured by Hayashi Kasei Co., Ltd.) (Dispersant) Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) (Dispersion aid) Sodium alkyl sulfonate (Latemul PS manufactured by Kao Corporation) (Crosslinking agent) t - Butyl peroxy - 2 - ethylhexyl carbonate (content 97%) (Perbutyl E manufactured by NOF Corporation) 〔Measurement method〕 Regarding the evaluation methods performed in the examples and comparative examples, they are explained below.

[0092] (Measurement of the weight per one loosened biodegradable resin particle) The weight per one resin particle was measured using an electronic balance (AUW120D manufactured by Shimadzu Corporation). The specific operation procedure was as follows: (1) 100 resin particles were randomly taken; (2) The weight of 100 resin particles was measured; (3) The value obtained by dividing the weight obtained in (2) by 100 was taken as the weight per one resin particle.

[0093] (Measurement of the length and diameter of one loosened biodegradable resin particle) The length and diameter of the resin particles were measured using a digital caliper (manufactured by Mitutoyo). For the resin particle length / diameter (the ratio of length to diameter), the x-direction of the resin particles defined above was taken as the length of the resin particles, and the average value of the lengths of line segment y and line segment z was taken as the diameter of the resin particles.

[0094] (Measurement of the melting point of resin particles) The melting point of the resin particles was measured using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Science Corporation). The specific operation procedure was as follows (1) - (3): (1) Approximately 5 mg of resin particles were weighed; (2) The temperature of the resin particles was raised from 10°C to 190°C at a heating rate of 10°C / min to melt the resin particles; (3) The temperature of the highest-temperature melting peak of the DSC curve obtained in the process of (2) was taken as the melting point of the resin particles.

[0095] (Measurement of the MFR of resin particles) The measurement method of the MFR of the resin particles was determined by measuring according to JIS K7210 using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho) with a load of 2.16 kg or 5 kg and a measurement temperature between 160 - 190°C.

[0096] (Dischargeability in the crushing process) After loosening the resin particles in the crushing process, the cover of the crusher (corresponding to cover 50 shown in Figure 1) was removed. Then, the inside of the cylindrical screen with many holes and the bottom plate were visually inspected, and the dischargeability in the crushing process was evaluated according to the following criteria. 〇: Almost no resin particles remained inside the cylindrical screen and on the bottom plate. ×: A large amount of resin particles remained inside the cylindrical screen and on the bottom plate.

[0097] (Measurement of the apparent density of the foamed particles) The method for measuring the apparent density of the foamed particles was as follows: (1) Measure the weight Wd (g) of the foamed particles; (2) Prepare a graduated cylinder filled with ethanol, and put the total amount of the foamed particles with the weight Wd into the graduated cylinder; (3) Use a wire mesh or the like to sink the foamed particles, and read the volume Vd (L) of the foamed particles from the rise in the water level of ethanol caused thereby; (4) Calculate the apparent density of the foamed particles according to the following formula; Apparent density (g / L) = Wd / Vd.

[0098] (Measurement of the length and diameter of the foamed particles) The length and diameter of the foamed particles were measured using a digital caliper (manufactured by Mitutoyo Corporation). The x-direction of the resin particles defined in [description] was taken as the length of the foamed particles, and the average value of the lengths of line segment y and line segment z was taken as the diameter of the foamed particles.

[0099] (Measurement of the closed-cell ratio of the foamed particles) For the foamed particles, in accordance with the method described in Procedure C of ASTM D2856-87, using an air comparison pycnometer [manufactured by Tokyo Science Co., Ltd., model 1000], the volume Vc (cm 3 ) was measured. Then, the total amount of the foamed particles after measuring Vc was submerged in a graduated cylinder filled with ethanol, and the apparent volume Va (cm 3 ) of the foamed particles was obtained from the rise in the water level of the graduated cylinder (water immersion method). The closed-cell ratio of the foamed particles was determined from 100 - (Va - Vc) × 100 / Va (%).

[0100] (Measurement of the internal pressure of the foamed particles) The method for measuring the internal pressure of the expanded particles was as follows: (1) The weight W1 (g) of the expanded particles after the pressurization step was measured; (2) The expanded particles were heated at 150 °C for 30 minutes to dissipate the inorganic gas inside the expanded particles; (3) For the expanded particles from which the inorganic gas had been dissipated, the weight W2 (g) of the expanded particles was measured again; (4) The weight of the inorganic gas (ΔW) was calculated from the weight difference (W1 - W2) of the expanded particles before and after the dissipation of the inorganic gas; (5) The internal pressure P (MPa (absolute pressure)) of the expanded particles was calculated from the ideal gas state equation (specifically, the following formula): Internal pressure P (MPa (absolute pressure)) of the expanded particles = (1 + ΔW / M × 0.082 × (273 + T) × (ρ × 1000 / W2)) / 9.87 In the above formula, M is the average molar molecular weight of the inorganic gas, T is the temperature (room temperature) when the weight of the expanded particles after the pressurization step was measured, and ρ is the apparent density (g / cc) of the expanded particles (expanded particles with weight W1) after the pressurization step.

[0101] (Measurement of the density of the foamed molded body) The method for measuring the density of the foamed molded body was as follows: (1) Using a digital caliper (manufactured by Mitutoyo Corporation), the length in the longitudinal direction (mm), transverse direction (mm), and thickness direction of the obtained foamed molded body was measured, and the volume V (L) of the foamed molded body was calculated; (2) The weight W (g) of the foamed molded body was measured; (3) Based on the following formula, the density of the foamed molded body was calculated; Density of the foamed molded body (g / L) = W / V.

[0102] <Example 1> (Method for manufacturing resin particles) (Granulation step) For the melt-kneading of the biodegradable resin composition, a twin-screw extruder (TEM-26SX manufactured by Toshiba Machine Co., Ltd.) was used. First, 100 parts by weight of biodegradable resin-1 and 0.10 parts by weight of talc were weighed and dry-blended to prepare a biodegradable resin composition. The prepared biodegradable resin composition was fed into the twin-screw extruder, and the biodegradable resin composition was melt-kneaded at a discharge rate of 60 kg / hr and a cylinder set temperature of 130°C to 160°C. The melt-kneaded biodegradable resin composition at 185°C was discharged from 40 holes of a Φ3 mm nozzle of a die attached to the tip of the extruder. The discharged biodegradable resin composition was water-cooled with water at 43°C and then cut to a length of 2.40 mm to obtain resin particles that adhered to each other.

[0103] (Crushing process and sizing process) The resin particles that adhered to each other were crushed using a crusher (Power Mill P-3S manufactured by Dalton Co., Ltd.). This crusher is equipped with 8 knives. The opening of the cylindrical screen was set to Φ2.5 mm, and the rotational speed of the knives was set to 4000 rpm to loosen the resin particles that adhered to each other. At this time, no resin particles remained inside the cylindrical screen and on the bottom plate, and the dischargeability was good.

[0104] Next, the loosened resin particles were sieved using a circular vibrating sieve (KFCR-500-2DC manufactured by Kowa Kogyosho Co., Ltd.). This circular vibrating sieve is equipped with an upper wire mesh and a lower wire mesh. The opening of the upper wire mesh is 1.40 mm, and the opening of the lower wire mesh is 0.85 mm. Among the sieved resin particles, the resin particles that passed through the upper wire mesh and did not pass through the lower wire mesh were regarded as good products, the resin particles that did not pass through the upper wire mesh were regarded as adhered products, and the resin particles that passed through the lower wire mesh were regarded as fine products. The yield of good products of the obtained resin particles was 96.3%. Also, the good product resin particles had a melting point of 145°C, an MFR measured at 160°C - 5 kg of 2.3 g / 10 min, a weight per piece of 2.0 mg, a length of 2.40 mm, and a diameter of 0.95 mm.

[0105] (Manufacture of expanded particles) 100 parts by weight of good resin particles obtained by the above (method for producing resin particles), 200 parts by weight of pure water, 1.0 part by weight of a dispersant, 0.1 part by weight of a dispersion aid, and 2 parts by weight of a crosslinking agent were charged into a pressure-resistant container under stirring. Then, ventilation was sufficiently carried out with carbon dioxide to remove oxygen in the pressure-resistant container.

[0106] Next, carbon dioxide was supplied as a foaming agent into the pressure-resistant container. Then, the temperature in the pressure-resistant container was raised to a foaming temperature of 129.5 °C. Further, carbon dioxide was supplied to the pressure-resistant container to increase the pressure in the pressure-resistant container to a foaming pressure of 3.3 MPa (gauge pressure). Subsequently, the temperature and pressure in the pressure-resistant container were each maintained for 60 minutes near the foaming temperature and foaming pressure. Then, the valve at the bottom of the pressure-resistant container was opened, and the content of the pressure-resistant container was discharged to atmospheric pressure through an opening orifice with a diameter of 3.6 mm to obtain P3HA-based foamed particles. After washing the dispersant and the like adhering to the surface of the foamed particles with water, the foamed particles were dried at 75 °C. The apparent density of the foamed particles obtained as described above was 70 g / L, the length / diameter was 1.0, and the closed-cell ratio was 98%.

[0107] (Manufacture of foamed molded body) The foamed particles obtained by the above (manufacture of foamed particles) were supplied to a pressure-resistant container heated to 80 °C. With the temperature in the pressure-resistant container maintained at 80 °C, the foamed particles in the pressure-resistant container were pressure-treated using air to set the internal pressure of the foamed particles to 0.17 MPa (absolute pressure). The foamed particles (foamed particles with internal pressure applied) inside the pressure-resistant container were taken out.

[0108] The foamed particles with internal pressure applied were filled into a mold. As the mold, a mold having a molding space of 370 mm in length × 320 mm in width × 60 mm in thickness, which was mounted on a molding machine (EP-900L-M5 manufactured by DAISEN Co., Ltd.), was used.

[0109] Subsequently, the foamed particles in the mold were heated with superheated steam at 0.15 MPa (gauge pressure) to obtain a foamed molded body. The obtained foamed molded body was taken out of the mold and dried at 75 °C. The density of the foamed molded body was 47 g / L, which was good.

[0110] <Examples 2 to 4> Resin particles were produced and sieved in the same manner as in Example 1, except that the crushing conditions were changed as shown in Table 1. The measurement results of each physical property and each evaluation result are shown in Table 1.

[0111] <Example 5> For the agglomerated products that did not pass through the upper wire mesh in the sieving of Example 1, the crushing process and sieving were performed again in the same manner as in Example 1. The yield of good-quality resin particles obtained was 99.4%. The good-quality resin particles had a melting point of 145°C, an MFR measured at 160°C - 5 kg of 2.3 g / 10 min, a weight per particle of 2.0 mg, a length of 2.40 mm, and a diameter of 0.95 mm.

[0112] <Example 6> (Pelletizing process) Resin particles that adhered to each other were obtained in the same manner as in Example 1, except that the cutting conditions were changed so that the length of the melt-kneaded biodegradable resin composition became 1.45 mm.

[0113] (Crushing process and sizing process) The resin particles that adhered to each other were loosened in the same manner as in Example 1, except that the opening of the cylindrical screen was set to Φ1.5 mm and the rotational speed of the knife was set to 4000 rpm. At this time, no resin particles remained inside the cylindrical screen and on the bottom plate, and the dischargeability was good.

[0114] Next, the sieving of the loosened resin particles was performed in the same manner as in Example 1, except that the opening of the lower wire mesh of the sieve was set to 1.0 mm. The yield of good-quality resin particles obtained was 95.7%. The good-quality resin particles had a melting point of 145°C, an MFR measured at 160°C - 5 kg of 2.3 g / 10 min, a weight per particle of 1.5 mg, a length of 1.45 mm, and a diameter of 1.05 mm.

[0115] <Example 7> (Pelletizing process) As the biodegradable resin, resin particles adhered to each other in the same manner as in Example 1 were obtained, except that biodegradable resin - 2 was used instead of biodegradable resin - 1, and the discharged biodegradable resin composition was changed to water cooling with water at 20°C.

[0116] (Crushing process and sizing process) The resin particles adhered to each other in the same manner as in Example 1 were loosened. At this time, no resin particles remained inside the cylindrical screen and on the bottom plate, and the discharge property was good.

[0117] Next, the resin particles loosened in the same manner as in Example 1 were sieved. The yield of good-quality resin particles obtained was 98.3%. Also, the good-quality resin particles had a melting point of 85°C, an MFR measured at 190°C - 2.16 kg of 4.2 g / 10 min, a weight per piece of 2.1 mg, a length of 2.40 mm, and a diameter of 0.95 mm.

[0118] <Example 8> (Pelletizing process) As the biodegradable resin, resin particles adhered to each other in the same manner as in Example 7 were obtained, except that biodegradable resin - 3 was used instead of biodegradable resin - 2.

[0119] (Crushing process and sizing process) The resin particles adhered to each other in the same manner as in Example 1 were loosened. At this time, no resin particles remained inside the cylindrical screen and on the bottom plate, and the discharge property was good.

[0120] Next, the resin particles loosened in the same manner as in Example 1 were sieved. The yield of good-quality resin particles obtained was 94.3%. Also, the good-quality resin particles had a melting point of 60°C, an MFR measured at 160°C - 2.16 kg of 3.1 g / 10 min, a weight per piece of 1.9 mg, a length of 2.40 mm, and a diameter of 0.95 mm.

[0121] <Example 9> After the granulation process, the crushing process, and the sizing process, foamed particles and a foamed molded article were produced in the same manner as in Example 1, except that resin particles that had not been sieved were used. The apparent density of the obtained foamed particles was 71 g / L, the length / diameter was 1.0, and the closed cell ratio was 98%. Also, the density of the obtained foamed molded article was 47 g / L, which was good.

[0122] <Comparative Example 1> (Method for producing resin particles) In Example 1, the granulation process was carried out to produce resin particles that adhered to each other, and the crushing process was not carried out.

[0123] The resin particles that adhered to each other were sieved in the same manner as in Example 1. As a result, the good product yield of the obtained resin particles was 3.8%.

[0124] (Production of foamed particles) Except for using 100 parts by weight of the resin particles that adhered to each other obtained by the above (Method for producing resin particles), an attempt was made to produce foamed particles in the same manner as in Example 1. However, the resin particles that adhered to each other clogged the orifice openings, and foamed particles could not be obtained.

[0125] <Comparative Examples 2 to 4> As shown in Table 1, resin particles were produced in the same manner as in Example 1, except that the crushing conditions were changed, and the resin particles were sieved. The measurement results of each physical property and each evaluation result are shown in Table 1.

[0126] <Comparative Example 5> In the crushing process, instead of a power mill, a ribbon mixer (manufactured by Satake Chemical Machinery Co., Ltd.) without a cylindrical screen was used, and the resin particles were produced and sieved in the same manner as in Example 1, except that the rotational speed of the ribbon blades was set to 55 rpm and the treatment was carried out for 5 minutes. In Comparative Example 5, the sizing process was not carried out. The results are summarized in Table 2.

[0127]

Table 1

[0128] As shown in Table 1, in Examples 1 to 9 where the crushing process was carried out, the dischargeability was good and the productivity of the resin particles was high. Furthermore, the yield of non-agglomerated good biodegradable resin particles was high.

[0129] On the other hand, in Comparative Example 1 where the crushing process was not carried out, the yield of good biodegradable resin particles was very low. Also, in Comparative Example 1, foamed particles could not be produced.

[0130] In Comparative Example 2, the opening of the cylindrical screen is Φ2.0 mm, while the length of one loosened resin particle is 2.4 mm. That is, in Comparative Example 2, the opening of the cylindrical screen is less than the length of one loosened resin particle. Since the opening of the cylindrical screen is less than the length of one loosened resin particle in this way, the dischargeability in the crushing process was poor. Therefore, loosened resin particles could not be obtained stably and continuously.

[0131] In Comparative Example 3, the opening of the cylindrical screen is Φ8.0 mm, while the length of the loosened resin particle is 2.4 mm. That is, in Comparative Example 3, the opening of the cylindrical screen is longer than three times the length of one loosened resin particle. Since the opening of the cylindrical screen is longer than three times the length of one loosened resin particle in this way, the yield of good products was low.

[0132] In Comparative Example 4, the rotational speed of the knife is 100 rpm, which is less than 500 rpm. For this reason, the dischargeability in the crushing process was poor. Therefore, loosened resin particles could not be obtained stably and continuously.

[0133] In Comparative Example 5, the rotational speed was low and the impact on the agglomerated resin particles was too weak, so it was difficult to loosen them and the yield of good products was low.

[0134] From the results of Examples 1 to 9 and Comparative Examples 1 to 5, it was confirmed that by performing the crushing step under specific conditions, the productivity of the biodegradable resin particles can be increased, and biodegradable resin particles that are not adhered to each other can be produced.

Industrial Applicability

[0135] The present invention can be suitably used for the production of food containers, packaging materials, sanitary products, garbage bags, packaging cushioning materials, agricultural boxes, fish boxes, automobile members, building materials, civil engineering materials, and the like.

Explanation of Symbols

[0136] 1 Resin particles 2 Resin particles (disentangled biodegradable resin particles) 10 Knife 20 Cylindrical screen 100 Crusher

Claims

1. A granulation step of obtaining adhered biodegradable resin particles by extruding a melt-kneaded biodegradable resin composition through a die and cutting it into a predetermined size; A disintegration step of loosening the adhered biodegradable resin particles by the impact of a rotating knife to obtain loosened biodegradable resin particles, The disintegration step includes a sizing step of passing the loosened biodegradable resin particles through a cylindrical screen installed outside the knife, The rotational speed of the knife is 1000 rpm to 5000 rpm, The mesh opening of the cylindrical screen is not less than the length of one of the loosened biodegradable resin particles and not more than three times the length of one of the loosened biodegradable resin particles. (Here, the length of one biodegradable resin particle is the maximum value of the distance between two cut surfaces that appears on the biodegradable resin particle when cutting the biodegradable resin particle in the manufacturing process of the biodegradable resin particle), a method for manufacturing biodegradable resin particles.

2. In the granulation step, after cooling the biodegradable resin composition discharged from the die, the biodegradable resin composition is cut into a predetermined size. The method for manufacturing biodegradable resin particles according to Claim 1.

3. Each of the loosened biodegradable resin particles has a weight of 0.3 to 10 mg per particle and a length / diameter ratio of 0.7 to 3. The method for manufacturing biodegradable resin particles according to Claim 1 or 2.

4. The biodegradable resin is at least one selected from the group consisting of poly(3-hydroxyalkanoate), polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, polycaprolactone, modified starch, and modified cellulose. The method for manufacturing biodegradable resin particles according to any one of Claims 1 to 3.

5. The method for producing biodegradable resin particles according to any one of claims 1 to 3, wherein the biodegradable resin is poly(3-hydroxyalkanoate).

6. The method for producing biodegradable resin particles according to claim 5, wherein the poly(3-hydroxyalkanoate) is at least one selected from the group consisting of poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate).

7. A method for producing biodegradable resin foam particles, comprising foaming the biodegradable resin particles obtained by the method for producing biodegradable resin particles according to any one of claims 1 to 6.

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