Poly(3-hydroxyalkanoate)-based resin foam particles

Abstract

The present invention addresses the problem of providing P3HA-based resin foam particles with which it is possible to provide P3HA-based resin foam moldings have excellent strength in a cryogenic environment. The above-mentioned problem is solved by providing P3HA-based resin foam particles obtained by foaming resin particles containing a P3HA-based resin, wherein the resin particles contain at least two types of P3HA-based resins having different structural unit compositions, and have a glass transition temperature of 2.0°C or less.

Description

Poly(3-hydroxyalkanoate) resin expanded particles

[0001] The present invention relates to expanded poly(3-hydroxyalkanoate) resin beads and molded articles thereof.

[0002] Large amounts of petroleum-derived plastics are discarded every year, and the resulting lack of landfill sites and environmental pollution are becoming serious issues. Microplastics have also become a major problem in the marine environment in recent years. For this reason, biodegradable plastics, which can be decomposed by microorganisms in marine and soil environments, as well as in landfills and compost, have attracted attention.

[0003] Biodegradable plastics are being developed with the aim of achieving a wide range of applications, including agricultural, forestry, and fishery materials that are used in the environment, as well as food containers, packaging materials, sanitary products, garbage bags, etc. Furthermore, foams made from biodegradable plastics are expected to be used in packaging cushioning, agricultural product boxes, fish boxes, automotive components, building materials, civil engineering materials, etc.

[0004] Among the biodegradable plastics, poly(3-hydroxyalkanoate) (hereinafter also referred to as "P3HA")-based resins have been attracting attention as plastics derived from plant raw materials due to their excellent biodegradability and carbon neutrality.

[0005] Conventionally, development of technologies relating to biodegradable plastics has been progressing. For example, Patent Document 1 discloses expanded beads obtained using a biodegradable P3HA-based resin and a foamed molded article obtained by in-mold foam molding of the expanded beads.

[0006] International Publication No. 2019 / 146555

[0007] However, the above-mentioned conventional techniques have room for improvement in terms of obtaining sufficient strength for foamed molded articles obtained by molding expanded P3HA resin beads when used in an extremely low temperature environment (-20°C or lower).

[0008] Therefore, one aspect of the present invention aims to provide expanded beads of a P3HA-based resin that can provide an expanded molded article of a P3HA-based resin that has excellent strength even in an extremely low temperature environment.

[0009] As a result of extensive research to solve the above-mentioned problems, the inventors have discovered that in expanded P3HA-based resin beads obtained by expanding resin particles containing P3HA-based resin, the resin particles contain two or more types of P3HA-based resin with different constitutional unit compositions, and the glass transition temperature (Tg) of the expanded P3HA-based resin beads is set within a specific range, thereby making it possible to obtain expanded molded P3HA-based resin articles that have excellent strength even when used in an extremely low temperature environment, and have completed the present invention.

[0010] Therefore, one aspect of the present invention is expanded P3HA-based resin particles obtained by expanding resin particles containing a P3HA-based resin, wherein the resin particles contain two or more types of P3HA-based resin having different constitutional unit compositions, and the expanded P3HA-based resin particles have a glass transition temperature of 2.0°C or lower.

[0011] According to one aspect of the present invention, it is possible to provide expanded beads of a P3HA-based resin, which can provide an expanded molded article of a P3HA-based resin that has excellent strength even in an extremely low temperature environment.

[0012] An embodiment of the present invention will be described in detail below. In this specification, unless otherwise specified, the numerical range "A to B" means "A or more and B or less."

[0013] [1. Overview of the Invention] As described above, conventional techniques for foamed molded articles obtained by molding expanded P3HA resin beads have room for improvement in terms of obtaining sufficient strength when used in an extremely low temperature (−20° C. or lower) environment.

[0014] Therefore, the present inventors conducted extensive research to solve the above-mentioned problems and found for the first time that, in the production of expanded P3HA resin beads obtained by expanding resin particles containing a P3HA resin, it is possible to obtain expanded molded P3HA resin articles that have excellent strength even when used in a cryogenic environment by using resin particles containing two or more types of P3HA resins with different constitutional unit compositions and setting the glass transition temperature of the expanded P3HA resin beads to 2.0° C. or lower. Even a person skilled in the art could not predict that the improvement in strength in a cryogenic environment would be achieved from the constitutional units of the P3HA resin and the glass transition temperature of the expanded P3HA resin beads, and this is a surprising effect.

[0015] The expanded P3HA resin beads according to one embodiment of the present invention can provide a P3HA resin foamed molded article that exhibits excellent strength even in a cryogenic environment, and are therefore extremely useful in applications particularly in a cryogenic environment. In this specification, "cryogenic environment" refers to an environment of -20°C or below.

[0016] Furthermore, the above-described configuration makes it possible to provide a foamed molded article of a P3HA-based resin that has excellent strength even in cryogenic environments, which can contribute to the achievement of the Sustainable Development Goals (SDGs), such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development." The present invention will be described in detail below.

[0017] 2. Expanded P3HA-based resin beads Expanded P3HA-based resin beads according to one embodiment of the present invention are obtained by expanding resin particles containing a P3HA-based resin, the resin particles containing two or more types of P3HA-based resins having different constitutional unit compositions, and the expanded P3HA-based resin beads have a glass transition temperature of 2.0° C. or lower. In this specification, "expanded P3HA-based resin beads" are also referred to as "expanded beads."

[0018] [2-1. P3HA-based resin] A P3HA-based resin according to one embodiment of the present invention is a polymer having a 3-hydroxyalkanoate unit as an essential structural unit (monomer unit). In this specification, "3-hydroxyalkanoate" may also be referred to as "3HA." Specifically, the P3HA-based resin is preferably a polymer containing a repeating unit represented by the following general formula (1): [-CHR-CH ２ -CO-O-]...(1).

[0019] In general formula (1), R represents an alkyl group represented by CnH2n+1, and n represents an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. n is preferably 1 to 10, and more preferably 1 to 8.

[0020] As the P3HA-based resin, a P3HA-based resin produced by a microorganism is particularly preferred. The P3HA-based resin produced by a microorganism is a poly[(R)-3HA] in which all 3HA units are (R)-3HA.

[0021] The P3HA resin preferably contains 3HA units (particularly repeating units of general formula (1)) in an amount of 50 mol% or more, more preferably 70 mol% or more, and even more preferably 80 mol% or more, of 100 mol% of all repeating units in the P3HA resin. Furthermore, the repeating units (monomer units) may consist solely of 3HA units, or may contain, in addition to 3HA units, repeating units derived from monomers other than 3HA (e.g., 4-hydroxyalkanoate units, etc.).

[0022] Specific examples of 3HA units include 3-hydroxybutyrate units, 3-hydroxyvalerate units, and 3-hydroxyhexanoate units. 3-Hydroxybutyrate has a melting point and tensile strength close to those of propylene. Therefore, it is preferable that a P3HA-based resin according to one embodiment of the present invention contains a 3-hydroxybutyrate unit. In this specification, "3-hydroxybutyrate" will also be referred to as "3HB" hereinafter.

[0023] The P3HA resin preferably contains 3HB units (monomer units) in an amount of 65 mol % or more, and more preferably 70 mol % or more, of the total repeating units (100 mol %) of the P3HA resin. As the P3HA, a polymer containing 3HB units, in which all the 3HB is (R)-3HB (a polymer produced by a microorganism) is particularly preferred.

[0024] When a P3HA-based resin contains two or more types of repeating units, the monomer from which the repeating units other than the repeating unit with the largest content are derived is referred to as a comonomer. In this specification, a "repeating unit derived from a comonomer" is also referred to as a "comonomer unit" hereinafter.

[0025] The comonomer is not particularly limited, but 3-hydroxyhexanoate (hereinafter also referred to as 3HH) or 4-hydroxybutyrate (hereinafter also referred to as 4HB) is preferred.

[0026] Specific examples of P3HA-based resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter, sometimes referred to as "P3HB3HV"); poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate); and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter, sometimes referred to as "P3HB3HH"). Examples thereof include poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter, sometimes referred to as "P3HB4HB"). In particular, from the viewpoints of processability and the physical properties of foamed molded articles, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is more preferred.

[0027] In this specification, P3HA-based resins with the same name (compound name) but different content ratios (monomer ratios) of the structural units (monomer units and comonomer units) that make up the P3HA-based resin are considered to be different types of P3HA-based resins. Therefore, as the P3HA-based resin, only P3HA-based resins with the same name (compound name) but different monomer ratios may be used from among the P3HA-based resins described above, or P3HA-based resins with different names may be used in combination.

[0028] The P3HA resin preferably has a 3HB unit as an essential structural unit and also has a comonomer unit. That is, the P3HA resin is preferably a copolymer having a 3HB unit and a comonomer unit. When the P3HA resin has a 3HB unit and a comonomer unit, the ratio of the 3HB unit to the comonomer unit (3HB unit / comonomer unit) in 100 mol% of all structural units in the P3HA resin is preferably 99.0 / 1.0 (mol% / mol%) to 69.0 / 31.0 (mol% / mol%), more preferably 98.5 / 1.5 (mol% / mol%) to 69.5 / 30.5 (mol% / mol%), and even more preferably 98.0 / 2.0 (mol% / mol%) to 70.0 / 30.0 (mol% / mol%). If the ratio of comonomer units to 100 mol% of all structural units of the P3HA resin is 1.0 mol% or more, the melt-mixable temperature range of the P3HA resin and the thermal decomposition temperature range are sufficiently separated, which has the advantage of a wide preferred molding process range. On the other hand, if the ratio of comonomer units to 100 mol% of all structural units of the P3HA resin is 31.0 mol% or less, the P3HA resin composition crystallizes quickly during melt-mixing, resulting in high productivity. The content ratio of each monomer unit in the P3HA resin can be determined by methods known to those skilled in the art, such as the method described in WO 2013 / 147139.

[0029] The melting point of the P3HA resin is not particularly limited, but is preferably 110.0° C. to 165.0° C., more preferably 120.0° C. to 155.0° C., and even more preferably 130.0° C. to 145.0° C. If the melting point of the P3HA resin is 110.0° C. or higher, there is no risk of the resulting foamed molded article changing in size upon heating, while if the melting point of the P3HA resin is 165.0° C. or lower, there is no risk of hydrolysis occurring during the foaming step.

[0030] The melting point of the P3HA resin was measured by differential scanning calorimetry (hereinafter also referred to as "DSC"), specifically as follows: (1) weigh out 5 to 6 mg of P3HA; (2) raise the temperature of the P3HA from 10.0°C to 190.0°C at a rate of 10.0°C / min to melt the P3HA; (3) determine the melting point of the P3HA from the temperature of the highest melting peak in the DSC curve of the P3HA obtained in step (2).

[0031] The weight-average molecular weight of the P3HA resin is not particularly limited, but is preferably 200,000 to 2,000,000, more preferably 250,000 to 1,500,000, and even more preferably 300,000 to 1,000,000. If the weight-average molecular weight of P3HA is 200,000 or more, there is no risk of the closed cell ratio of the resulting expanded beads being low. On the other hand, if the weight-average molecular weight is 2,000,000 or less, the load on the machine when melt-kneading the P3HA composition is reduced, resulting in good productivity. The weight-average molecular weight of P3HA can be measured from the polystyrene-equivalent molecular weight distribution using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. As the column for this gel permeation chromatography, a known column suitable for measuring weight-average molecular weight may be used.

[0032] In one embodiment of the present invention, the method for producing a P3HA-based resin is not particularly limited, and may be a production method by chemical synthesis or a production method using a microorganism. Among these, a production method using a microorganism is preferred. As a method for producing P3HA using a microorganism, known methods such as those described in WO 2009 / 145164 and WO 2019 / 142845 can be applied.

[0033] The microorganism that produces microbially produced P3HA is not particularly limited as long as it is a microorganism capable of producing P3HAs. For example, the first P3HB-producing bacterium was Bacillus megaterium, discovered in 1925, and other natural microorganisms include Cupriavidus necator (formerly classified as Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. It is known that P3HB accumulates in the cells of these microorganisms.

[0034] Specific examples of bacteria that produce copolymers of 3HB and other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, with regard to P3HB3HH, Alcaligenes eutrophus AC32 strain (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) is more preferred, in which P3HB3HH productivity has been improved by introducing genes encoding the P3HA synthase group. In the method for producing P3HA, microbial cells obtained by culturing microorganisms such as Alcaligenes eutrophus AC32 strain under appropriate conditions and allowing P3HB3HH to accumulate within the cells are preferably used. In addition to the copolymer-producing bacteria described above, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may also be used depending on the P3HA to be produced. Furthermore, various culture conditions for the microorganisms (bacteria), including the type of substrate, may be optimized depending on the P3HA to be produced.

[0035] [2-2. P3HA-based Resin Particles] The P3HA-based resin particles of the present invention are particles comprised of a composition (P3HA-based composition) containing P3HA as an essential component, and include two or more types of P3HA-based resins with different constitutional unit compositions. In this specification, "different constitutional unit compositions" of P3HA-based resins includes both cases where "the types of constitutional units constituting the P3HA-based resin are different" and cases where "the P3HA-based resin contains two or more types of the same constitutional units but the content ratios (monomer ratios) of the constitutional units are different."

[0036] The composition typically contains a P3HA resin and, if necessary, additives. In this specification, "(3-hydroxyalkanoate) resin particles" are also referred to as "resin particles." In this specification, "resin particles" refers to particles that have not yet been expanded and are not yet subjected to the expansion step.

[0037] The content of P3HA-based resin in the resin particles is not particularly limited, but since the resulting expanded beads and foamed molded articles have excellent biodegradability, it is preferably 70% by weight or more, and more preferably 80% by weight or more, relative to 100% by weight of the expanded beads.

[0038] When the P3HA resin contained in the resin particles is a copolymer having 3HB units and comonomer units, the average content of the comonomer units in 100 mol% of all repeating units in the copolymer is preferably 6.5 to 12.0 mol%, more preferably 6.6 to 11.8 mol%, and even more preferably 6.7 to 11.6 mol%. If the average content of the comonomer units in 100 mol% of all repeating units in the copolymer is 6.5 to 12.0 mol%, the copolymer has the advantage of excellent low-temperature strength.

[0039] From the viewpoint of excellent physical properties and / or moldability, the resin particles according to the present invention preferably contain P3HB3HH as the P3HA-based resin. The resin particles may contain P3HB3HH and a P3HA-based resin other than P3HB3HH, or may contain P3HB3HH(A) and P3HB3HH(B), which contain 3HB units and 3HH units and have different ratios (monomer ratios) of the 3HB units to the 3HH units.

[0040] When the P3HA resin contained in the resin particles is a copolymer having a 3HB unit and a comonomer unit, it is preferable to include a copolymer (A) having a comonomer unit content of 1.0 to 6.0 mol% of all repeating units (100 mol%) and a copolymer (B) having a comonomer unit content of 13.0 mol% or more of all repeating units (100 mol%). From the viewpoint of stability of crystallization rate, the comonomer unit content of 100 mol% of all repeating units in the copolymer (A) is preferably 1.0 to 6.0 mol%, more preferably 1.2 to 5.9 mol%, and even more preferably 1.4 to 5.8 mol%. Furthermore, from the viewpoint of ensuring strength at low temperatures, the comonomer unit content of 100 mol% of all repeating units in the copolymer (B) is preferably 13.0 mol% or more, more preferably 14.0 mol% or more, and even more preferably 15.0 mol% or more.

[0041] The weight of copolymer (A) contained in the resin particles is preferably 65% ​​or more, more preferably 70% or more, and even more preferably 75% or more, based on 100% by weight of the total of copolymer (A) and copolymer (B). This configuration has the advantage of being able to adjust the physical properties of the resulting foamed molded article.

[0042] The resin particles according to one embodiment of the present invention may contain additives as long as the effects of the present invention are not impaired. Examples of additives that can be used depending on the purpose include crystal nucleating agents, cell regulators, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, organic fillers, and hydrolysis inhibitors. Biodegradable additives are particularly preferred as additives. The "crystal nucleating agent" is also referred to as a "crystallization nucleating agent." For information on the type of additive, the amount of additive, and other usage methods, the types and usage methods described in WO 2021 / 002092 can be used, for example.

[0043] Examples of the crystal nucleating agent include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, etc. Among these, pentaerythritol is preferred because it has a particularly excellent effect of promoting the crystallization of P3HA.

[0044] The content of the nucleating agent in the resin particles is not particularly limited, but is preferably 0.1 to 5.0 parts by weight, more preferably 0.5 to 3.0 parts by weight, and even more preferably 0.7 to 1.5 parts by weight, relative to 100 parts by weight of P3HA. One type of nucleating agent may be used alone, or two or more types may be mixed and used. When two or more types of nucleating agents are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

[0045] Examples of the cell 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, talc is preferred because of its particularly excellent dispersibility in P3HA.

[0046] The content of the cell control agent in the resin particles is not particularly limited, but is preferably 0.01 to 1.0 parts by weight, more preferably 0.03 to 0.5 parts by weight, and even more preferably 0.05 to 0.3 parts by weight, relative to 100 parts by weight of P3HA. The cell control agent may be used alone or in combination with two or more different types. When two or more different cell control agents are used in combination, the mixing ratio may be adjusted appropriately depending on the purpose.

[0047] Examples of the lubricant include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, polycondensates of ethylenediamine, stearic acid, and sebacic acid, etc. Among these, behenamide and / or erucamide are preferred because of their particularly excellent lubricating effect on P3HA.

[0048] The content of the lubricant in the resin particles is not particularly limited, but is preferably 0.01 to 5.0 parts by weight, more preferably 0.05 to 3.0 parts by weight, and even more preferably 0.1 to 1.5 parts by weight, relative to 100 parts by weight of P3HA. One type of lubricant may be used alone, or two or more types may be mixed and used. When two or more types of lubricants are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

[0049] The resin particles according to one embodiment of the present invention may further contain resin components other than P3HA (also referred to as "other resin components"). Examples of the other resin components include (a) aliphatic polyesters such as polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone, and (b) aliphatic aromatic polyesters.

[0050] The content of the other resin components in the resin particles is not particularly limited, but is preferably 10 to 400 parts by weight, and more preferably 50 to 150 parts by weight, relative to 100 parts by weight of P3HA. One type of the other resin components may be used alone, or two or more types may be mixed and used.

[0051] The glass transition temperature of the resin particles is 1.0°C or lower, preferably 0.8°C or lower, and more preferably 0.6°C or lower. When the glass transition temperature of the resin particles is 1.0°C or lower, a foamed molded article of P3HA-based resin having excellent strength even when used in an extremely low temperature environment can be obtained. Furthermore, the lower limit of the glass transition temperature of the resin particles is not particularly limited, but is, for example, -8.0°C or higher, preferably -7.5°C or higher, more preferably -7.0°C or higher, and even more preferably -6.5°C or higher. In particular, when the lower limit of the glass transition temperature of the resin particles is -6.5°C or higher, an excellent shrinkage rate can be achieved.

[0052] The melting point of the resin particles (hereinafter sometimes referred to as "Tmp") is not particularly limited, but is preferably 110.0°C to 165.0°C, more preferably 120.0°C to 155.0°C, and even more preferably 130.0°C to 145.0°C. If the melting point of the resin particles is 110.0°C or higher, dimensional change due to heating during molding of the resulting expanded beads can be suppressed. On the other hand, if the melting point of the resin particles is 165.0°C or lower, there is no risk of P3HA being hydrolyzed during expansion of the resin particles. Note that components other than P3HA contained in the resin particles (e.g., additives) have almost no effect on the melting point of the resin particles. In other words, the melting point of the resin particles can also be said to be the melting point of the P3HA contained in the resin particles.

[0053] The melting point (Tmp) of the resin particles is measured by a differential scanning calorimeter (hereinafter referred to as the "DSC method"), and the specific procedure is as follows: (1) 5 mg to 6 mg of resin particles are weighed out; (2) the temperature of the resin particles is increased from 10°C to 190°C at a rate of 10°C / min to melt the resin particles; (3) the temperature of the highest melting peak in the DSC curve of the resin particles obtained in the process (2) can be determined as the melting point of the resin particles.

[0054] The melt flow rate (hereinafter also referred to as MFR) of the resin particles at 165°C is preferably 1.0 to 20.0 g / 10 min, more preferably 1.0 to 17.0 g / 10 min, and even more preferably 1.0 to 15.0 g / 10 min. When the MFR is 1.0 g / 10 min or more, expanded particles with a high apparent density can be obtained with only one expansion. When the MFR is 20.0 g / 10 min or less, the strength of the resulting foamed molded article is high. The MFR of the resin particles is determined using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7210, under conditions of a load of 5 kg and a measurement temperature of +5 to 10°C of the melting end temperature read from the DSC curve obtained in measuring the melting point of the resin particles.

[0055] The weight of each resin particle is not particularly limited, but is preferably 0.3 mg to 10.0 mg, and more preferably 0.5 mg to 5.0 mg. When the weight of each resin particle is 0.3 mg or more, the resin particles can be produced stably with high productivity. On the other hand, when the weight of each resin particle is 10.0 mg or less, the expanded particles obtained from the resin particles can easily provide thin-walled expanded molded articles.

[0056] The shape of the resin particles is not particularly limited, but the length-to-diameter ratio (length / diameter) is preferably 0.5 to 3.0, more preferably 1.5 to 2.7, and even more preferably 2.0 to 2.5. When the length / diameter ratio of the resin particles is 0.5 to 3.0, the resulting expanded beads are likely to be spherical or nearly spherical rather than flattened. Spherical or nearly spherical expanded beads have good filling properties in the molding cavity of the mold of a molding machine and can provide expanded molded articles with excellent surface aesthetics. Here, the length of a resin particle refers to the maximum distance between two cross sections that appear (or are generated) on the resin particle when the resin particle is cut during the resin particle production process. Next, when the length direction of the resin particle is the x direction, draw an arbitrary line y and a line z perpendicular to line y on a cross section (cross section x) perpendicular to the x direction. The line segment obtained by cutting line y at cross section x is called line segment y, and the line segment obtained by cutting line z at cross section x is called line segment z. The diameter of the resin particle means the average value of the length of the line segment y and the length of the line segment z.

[0057] (Resin particle preparation process) The resin particle preparation process according to one embodiment of the present invention is a process of preparing P3HA-based resin particles containing P3HA and, if necessary, additives. The resin particle preparation process can be carried out before the foaming process described below. The resin particle preparation process can also be said to be a process of molding a resin composition containing P3HA into a shape that is easy to use for foaming. The mode of the resin particle preparation process is not particularly limited as long as resin particles can be obtained.

[0058] The resin particle preparation step preferably includes: (a) a melt-kneading step of melt-kneading a resin composition containing P3HA and, if necessary, additives; and (b) a particle molding step of molding the melt-kneaded resin composition into a shape that is easy to use for foaming.

[0059] The mode of the melt-kneading step is not particularly limited as long as a melt-kneaded resin composition can be obtained. Specific examples of the melt-kneading step include the following methods (a1) and (a2): (a1) A method in which P3HA and, if necessary, additives are mixed or blended using a mixer or the like to prepare a resin composition, and then the resin composition is supplied to a melt-kneading device and melt-kneaded; (a2) A method in which P3HA and, if necessary, additives are supplied to a melt-kneading device, and a resin composition is prepared (completed) in the melt-kneading device, and the resin composition is melt-kneaded.

[0060] In the method (a1), the order in which P3HA and, if necessary, additives are mixed or blended (dry blended) is not particularly limited.In the method (a2), the order in which P3HA and, if necessary, additives are supplied to the melt-kneading apparatus is not particularly limited.

[0061] In the method (a1), the mixing device is not particularly limited, and examples thereof include a ribbon blender, a flash blender, a tumbler mixer, and a super mixer.

[0062] In the methods (a1) and (a2), the melt-kneading device is not particularly limited, and examples thereof include an extruder, a kneader, a Banbury mixer, a roll, etc. From the viewpoint of excellent productivity and convenience, the melt-kneading device is preferably an extruder, and more preferably a twin-screw extruder.

[0063] In the method (a1), the types and amounts of P3HA and additives used in mixing or blending determine the types and contents of P3HA and additives in the resulting resin particles. In the method (a2), the types and amounts of P3HA and additives supplied to the melt-kneading device determine the types and contents of P3HA and additives in the resulting resin particles. The types and contents of P3HA and additives in the resin particles determine the types and contents of P3HA and additives in the expanded beads obtained using the resin particles. Therefore, the types, amounts used, and amounts of additives are described in the above section (Additives). It is not necessary to use all of the additives used in the expanded bead production method in the resin bead preparation step. In other words, all or some of the additives (e.g., crosslinking agents) used in the expanded bead production method may be added to the dispersion in the subsequent expansion step (e.g., dispersion step) without being used in the resin bead preparation step, i.e., without being incorporated into the resin particles.

[0064] In the melt-kneading step, the temperature at which the resin composition is melt-kneaded cannot be generally specified because it depends on the physical properties of P3HA (melting point, weight-average molecular weight, etc.) and the type of additive 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 die nozzle (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 the resin composition being insufficiently melt-kneaded. On the other hand, when the composition temperature is 200°C or lower, there is no risk of the P3HA being thermally decomposed.

[0065] The form of the particle molding step is not particularly limited as long as the melt-kneaded resin composition can be molded into the desired shape. By using a melt-kneading device equipped with a die and a cutting device as the melt-kneading device, the melt-kneaded resin composition can be easily molded into the desired shape in the particle molding step. Specifically, the melt-kneaded resin composition is discharged from the nozzle of the die equipped in the melt-kneading device, and the resin composition is cut by the cutting device simultaneously with or after discharge, thereby molding into the desired shape. The shape of the obtained resin particles is not particularly limited, but cylindrical, elliptical, spherical, cubic, rectangular parallelepiped, etc. are preferred because they are easily usable for foaming.

[0066] In the particle molding step, the resin composition extruded from the die nozzle may be cooled. When the resin composition extruded from the die nozzle is cooled, the resin composition may be cut by a cutting device simultaneously with or after cooling.

[0067] In the particle molding step, when the resin composition discharged from the die nozzle is cooled, the temperature of the cooled resin composition (hereinafter sometimes referred to as the cooling temperature) is not particularly limited. The cooling temperature is preferably 20°C to 80°C, more preferably 30°C to 70°C, and even more preferably 40°C to 60°C. This configuration has the advantage that the melt-kneaded resin composition crystallizes sufficiently quickly, thereby improving the productivity of resin particles.

[0068] [2-3. Expanded P3HA Resin Beads] (Glass Transition Temperature of Expanded Beads) The glass transition temperature of the expanded beads is 2.0°C or lower, preferably 1.8°C or lower, and more preferably 1.6°C or lower. When the expanded beads have a glass transition temperature of 2.0°C or lower, a P3HA resin foam molded article having excellent strength can be obtained even when used in an extremely low temperature environment. The lower limit of the glass transition temperature of the expanded beads is not particularly limited, but is, for example, −6.5°C or higher, preferably −6.0°C or higher, more preferably −5.5°C or higher, and even more preferably −5.0°C or higher. In particular, when the lower limit of the glass transition temperature of the expanded beads is −5.0°C or higher, an excellent shrinkage rate can be achieved.

[0069] (Expansion Ratio of Expanded Beads) The expansion ratio of the expanded beads is preferably 20 to 60 times, more preferably 20 to 50 times, even more preferably 23 to 50 times, and particularly preferably 25 to 40 times. By using expanded beads having an expansion ratio in the above range, it is possible to obtain an expanded molded article having a good balance between mechanical strength and light weight. For the method of calculating the expansion ratio, please refer to the examples of the present application.

[0070] (Gel fraction of expanded beads) Expanded beads have a crosslinked structure. In this specification, the crosslinked structure of expanded beads is evaluated by the gel fraction of the expanded beads. The term "expanded beads have a crosslinked structure" means that the gel fraction of the expanded beads is 1% by weight or more relative to 100% by weight of the expanded beads. There are no particular limitations on the method for crosslinking the expanded beads, but examples include a method of adding a crosslinking agent during the production of the expanded beads, as described below.

[0071] The gel fraction of the expanded beads is preferably 65 to 90% by weight, more preferably 70 to 85% by weight, and even more preferably 72 to 83% by weight, based on 100% by weight of the expanded beads. When the gel fraction of the expanded beads is 65% by weight or more, based on 100% by weight of the expanded beads, the expanded beads have a wider molding temperature range in which a high-quality expanded molded article can be obtained, which is advantageous in that productivity is improved. When the gel fraction is 90% by weight or less, the expanded molded article has an advantage of being excellent in surface beauty.

[0072] In one embodiment of the present invention, the gel fraction of expanded beads is an index showing the degree of crosslinking of P3HA in the expanded beads. The gel fraction of expanded beads can be controlled by the type and / or amount of crosslinking agent used. For a method for measuring the gel fraction of expanded beads, please refer to the examples in this application.

[0073] (Average cell diameter of expanded beads) The average cell diameter of expanded beads is not particularly limited, but is preferably 270 μm or less, more preferably 250 μm or less. When the average cell diameter of expanded beads is 270 μm or less, there is an advantage that the molding cycle tends to be good. In addition, there is no particular limit to the lower limit of the average cell diameter of expanded beads, but it is preferably 50 μm or more, more preferably 100 μm or more, and even more preferably 140 μm or more. When the average cell diameter of expanded beads is 50 μm or more, there is an advantage that by molding the expanded beads, a foamed molded article with excellent surface beauty can be obtained.

[0074] In this specification, the average cell diameter of expanded beads is specifically a value obtained by measurement using the following methods (1) to (4): (1) cutting an expanded bead using a razor (for example, a high-stainless double-edged razor manufactured by Feather Corporation) so that the cut surface passes through the center of the expanded bead; (2) observing the resulting cut surface of the expanded bead using an optical microscope (for example, VHX-100 manufactured by Keyence Corporation) at a magnification of 50 times; (3) drawing a straight line passing through the center or approximately the center of the cut surface of the expanded bead in the image obtained by observation; (4) (4-1) measuring the number n of cells present on the line; (4-2) measuring the length of the line segment cut from the line at the intersection of the line with the surface of the expanded bead, and defining this as the expanded bead diameter L; (5) calculating the average cell diameter of the expanded beads using the following formula: average cell diameter (μm) = L / n.

[0075] (Bulk Density of Expanded Beads) The bulk density of the expanded beads is not particularly limited, but is preferably 20.0 g / L to 600.0 g / L, more preferably 30.0 g / L to 300.0 g / L, and even more preferably 32.0 g / L to 100.0 g / L. When the expanded beads have a bulk density of (a) 20.0 g / L or more, there is an advantage that a foamed molded article with excellent cushioning properties and / or mechanical strength tends to be obtained, and when the expanded beads have a bulk density of (b) 600.0 g / L or less, there is an advantage that a foamed molded article with excellent lightness tends to be obtained. For the method for measuring the bulk density of the expanded beads, please refer to the Examples of the present application.

[0076] (Method for producing expanded P3HA-based resin beads) The expanded P3HA-based resin beads of the present invention can be obtained by expanding the P3HA-based resin beads described above. The expansion step in this production method preferably includes: (a) a dispersing step of dispersing resin particles, an aqueous dispersion medium, a crosslinking agent, a blowing agent, and, if necessary, a dispersant and / or a dispersion aid in a container; (b) a temperature-pressure increasing step of increasing the temperature inside the container to a constant temperature and the pressure inside the container to a constant pressure; (c) a maintaining step of maintaining the temperature and pressure inside the container at a constant temperature and a constant pressure; and (d) a releasing step of opening one end of the container and releasing the dispersion inside the container into a region (space) where the pressure is lower than the expansion pressure (i.e., the pressure inside the container).

[0077] (a) Dispersion step The dispersion step can be said to be a step of preparing a dispersion in which resin particles, a crosslinking agent, a foaming agent, and optionally a dispersant, a crosslinking aid, a dispersion aid, and / or a plasticizer are dispersed in an aqueous dispersion medium. Note that in the dispersion, the crosslinking agent and the crosslinking aid are consumed by reaction with P3HA in the resin particles and may not be present, and the foaming agent and the plasticizer are impregnated in the resin particles and may not be present in a dispersed state.

[0078] The container is not particularly limited, but is preferably a container that can withstand the foaming temperature and foaming pressure described below, for example, a pressure-resistant container.

[0079] The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse resin particles, a crosslinking agent, a foaming agent, etc. For example, tap water and / or industrial water can be used as the aqueous dispersion medium. From the viewpoint of enabling stable production of expanded particles, it is preferable to use pure water such as RO water (water purified by a reverse osmosis membrane method), distilled water, deionized water (water purified by an ion exchange resin), or ultrapure water as the aqueous dispersion medium.

[0080] The amount of the aqueous dispersion medium used is not particularly limited, but is preferably 100 to 1000 parts by weight per 100 parts by weight of the resin particles.

[0081] In the method for producing expanded beads, a crosslinking agent is used. By using a crosslinking agent, the P3HA in the resulting expanded beads becomes P3HA with a crosslinked structure. In other words, expanded P3HA beads with an excellent gel fraction can be obtained. As a result, when molding a foamed molded article, the molding temperature range of the expanded beads that can provide a high-quality foamed molded article is broadened, which has the advantages of improving productivity and allowing foamed molded articles with excellent internal fusion to be obtained at low molding pressure. Because the crosslinking reaction of the P3HA in the resin beads also progresses during the foaming process, the foaming process can also be considered a crosslinking process.

[0082] The crosslinking agent is not particularly limited as long as it can crosslink P3HA. An organic peroxide is preferred as the crosslinking agent. In other words, the P3HA-based expanded beads are preferably crosslinked with an organic peroxide. The organic peroxide may be used in the resin particle production process, the dispersion process, or both the resin particle production process and the dispersion process. More specifically, to react the organic peroxide with P3HA, the organic peroxide and P3HA may be melt-kneaded in the resin particle production process, the resin particles and the organic peroxide may be dispersed in an aqueous dispersion medium in the dispersion process, or the organic peroxide and P3HA may be melt-kneaded and further dispersed in an aqueous dispersion medium. In the dispersion process, the resin particles produced in the resin particle production process and the organic peroxide are dispersed in an aqueous dispersion medium, thereby allowing the organic peroxide to be impregnated into and react with the resin particles. For these reasons, an organic peroxide is preferred as the crosslinking agent in the expanded bead production method. When an organic peroxide is used as the cross-linking agent, the molecular chains of P3HA bond directly to each other (without going through a structure derived from the cross-linking agent) to form a cross-linked structure.

[0083] Although it depends on the type of P3HA used, the organic peroxide used as the crosslinking agent is preferably an organic peroxide having a one-hour half-life temperature of 90° C. to 160° C., more preferably an organic peroxide having a one-hour half-life temperature of 105° C. to 125° C., and even more preferably an organic peroxide having a one-hour half-life temperature of 110° C. to 125° C. Specifically, benzoyl peroxide (BPO, one-hour half-life temperature: 92° C.), t-butylperoxy-2-ethylhexyl carbonate (TBEC, one-hour half-life temperature: 121° C.), t-butylperoxyisopropyl carbonate (TBIC, one-hour half-life temperature: 118° C.), t-amylperoxy-2-ethylhexyl carbonate (TAEC, one-hour half-life temperature: 117° C.), t-amylperoxyisopropyl carbonate (TAIC, one-hour half-life temperature: 115°C), t-butyl peroxyisobutyrate (1-hour half-life temperature: 93°C), t-butyl peroxy-2-ethylhexanoate (1-hour half-life temperature: 95°C), t-butyl peroxyisononanoate (1-hour half-life temperature: 123°C), t-butyl peroxyacetate (1-hour half-life temperature: 123°C), t-butyl peroxydibenzoate (1-hour half-life temperature: 125°C), t-amyl peroxyisobutyrate (1-hour half-life temperature: 93°C), t- Amylperoxy-2-ethylhexanoate (1-hour half-life temperature: 92°C), t-amylperoxyisononanoate (1-hour half-life temperature: 114°C), t-amylperoxyacetate (1-hour half-life temperature: 120°C), t-amylperoxybenzoate (1-hour half-life temperature: 122°C), dicumyl peroxide (1-hour half-life temperature: 137°C), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (1-hour half-life temperature: 140°C), di- Examples include t-butyl peroxide (one-hour half-life temperature: 149°C), 1,1-bis(t-butylperoxy)cyclohexane (TBCH, one-hour half-life temperature: 116°C), 2,2-di(t-butylperoxy)butane (one-hour half-life temperature: 127°C), 1,1-di(t-amylperoxy)cyclohexane (one-hour half-life temperature: 112°C), and 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane (one-hour half-life temperature: 114°C).The use of an organic peroxide having a one-hour half-life temperature of 90° C. or higher has the advantage that expanded beads having a desired gel fraction tend to be obtained, whereas the use of an organic peroxide having a one-hour half-life temperature of 160° C. or lower has the advantage that there is no risk of unreacted crosslinker remaining in the final product.

[0084] As the organic peroxide to be used as the crosslinking agent, an organic peroxide having a t-butoxy group and / or a cumyloxy group is more preferred, since the crosslinking of P3HA in the resulting expanded beads approaches uniform crosslinking. Specific examples of peroxides having a t-butoxy group and / or a cumyloxy group include t-butylperoxy-2-ethylhexyl carbonate (TBEC), t-butylperoxyisopropyl carbonate (TBIC), t-butylperoxyisobutyrate, t-butylperoxy-2-ethylhexanoate, t-butylperoxyisononanoate, t-butylperoxyacetate, t-butylperoxydibenzoate, dicumyl peroxide, 2,5-dimethyl-2,5-di(t-butylperoxy)hexane, di-t-butyl peroxide, 1,1-bis(t-butylperoxy)cyclohexane (TBCH), 2,2-di(t-butylperoxy)butane, and 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane. Furthermore, the use of organic peroxides having t-butoxy and / or cumyloxy groups has the advantage of being less environmentally hazardous than organic peroxides (e.g., BPO) that do not have t-butoxy and / or cumyloxy groups. Among organic peroxides having t-butoxy and / or cumyloxy groups, organic peroxides having t-butoxy and / or cumyloxy groups and peroxycarbonate groups are preferred because the crosslinking of P3HA in the resulting expanded beads is closer to uniform crosslinking.

[0085] The present inventors have independently discovered that, surprisingly, when an organic peroxide having a t-butoxy group and / or a cumyloxy group is used as a crosslinking agent, expanded beads whose internal pressure is difficult to reduce can be easily obtained. Therefore, when an organic peroxide having a t-butoxy group and / or a cumyloxy group is used as a crosslinking agent, expanded beads that can provide foamed molded articles with excellent fusibility can be easily obtained by applying a lower internal pressure than in the prior art.

[0086] The amount of crosslinking agent used is not particularly limited, but is preferably 0.1 to 5.0 parts by weight, more preferably 0.3 to 3.0 parts by weight, even more preferably 0.5 to 3.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight, per 100 parts by weight of resin particles. When the amount of crosslinking agent used is 0.1 parts by weight or more per 100 parts by weight of resin particles, (a) the resulting expanded beads can be sufficiently crosslinked, and (b) the resulting expanded beads have a high closed-cell content, resulting in a foamed molded article with good surface aesthetics and low molding shrinkage. On the other hand, when the amount of crosslinking agent used is 5.0 parts by weight or less per 100 parts by weight of resin particles, the effect corresponding to the amount of crosslinking agent used is obtained, and there is no risk of economic waste. The amount of crosslinking agent used is positively correlated with the gel fraction of the expanded beads and significantly affects the gel fraction value of the expanded beads. Therefore, it is desirable to strictly determine the amount of crosslinking agent used, taking into account the gel fraction of the resulting expanded beads. The resin particles used in the dispersion step may already contain a crosslinking agent. In such a case, it is preferable that the total amount of the crosslinking agent already contained in the resin particles before the dispersion step and the amount of the crosslinking agent used in the dispersion step falls within the above range.

[0087] Examples of blowing agents include inorganic gases such as nitrogen, carbon dioxide, and air; saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane; ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane; and water. The blowing agent may be at least one selected from the group consisting of the inorganic gases, saturated hydrocarbons having 3 to 5 carbon atoms, ethers, halogenated hydrocarbons, and water. Among these, nitrogen or carbon dioxide is preferred from the viewpoints of environmental impact and foaming power. These blowing agents may be used alone or in combination of two or more. When two or more blowing agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0088] The amount of foaming agent used is not particularly limited, but is preferably 2 to 10,000 parts by weight, more preferably 5 to 5,000 parts by weight, and even more preferably 10 to 1,000 parts by weight, per 100 parts by weight of resin particles. When the amount of foaming agent used is 2 parts by weight or more per 100 parts by weight of resin particles, expanded particles with a suitable density can be obtained. On the other hand, when the amount of foaming agent used is 10,000 parts by weight or less per 100 parts by weight of resin particles, the effect corresponding to the amount of foaming agent used is obtained, so economic waste does not occur.

[0089] In the method for producing expanded beads, it is preferable to use a dispersant. The use of a dispersant has the advantage of suppressing adhesion (sometimes referred to as blocking) between resin particles, thereby enabling stable production of expanded beads. Examples of dispersants include inorganic substances such as tribasic calcium phosphate, tribasic magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, aluminum oxide, titanium oxide, and aluminum hydroxide. These dispersants may be used alone or in combination of two or more. When two or more dispersants are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose. The amount of dispersant used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight, and more preferably 0.5 to 1.5 parts by weight, per 100 parts by weight of resin particles.

[0090] In the dispersion step, when the resin particles are impregnated with and reacted with a crosslinking agent and, if necessary, a crosslinking aid, it is preferable to lower the oxygen concentration in the container and the amount of dissolved oxygen in the dispersion in order to increase the crosslinking efficiency of P3HA. Methods for lowering the oxygen concentration in the container and the amount of dissolved oxygen in the dispersion include replacing the gas in the container and the gas dissolved in the dispersion with inorganic gases such as carbon dioxide and nitrogen, and evacuating the gas in the container.

[0091] In the method for producing expanded beads, a dispersing aid may be used to improve the effect of suppressing adhesion of resin particles to each other. Examples of dispersing aids include anionic surfactants such as sodium alkanesulfonate, sodium alkylbenzenesulfonate, and sodium α-olefinsulfonate. One of these dispersing aids may be used alone, or two or more may be used in combination. When two or more dispersing aids are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0092] The amount of the dispersing aid used is not particularly limited, but is preferably 0.001 to 0.5 parts by weight, and more preferably 0.01 to 0.2 parts by weight, relative to 100 parts by weight of the resin particles. In order to further improve the effect of suppressing adhesion of the resin particles to each other, it is preferable to use the dispersing agent and the dispersing aid in combination.

[0093] (b) Temperature-increase step and (c) retention step The temperature-increase step is preferably carried out after the dispersion step, and the retention step is preferably carried out after the temperature-increase step. In this specification, the constant temperature in the temperature-increase step and the retention step may be referred to as the foaming temperature, and the constant pressure in the foaming pressure may be referred to as the foaming pressure.

[0094] The foaming temperature cannot be generally defined, as it varies depending on the type of P3HA, the type of blowing agent, the desired apparent density of the expanded beads, and other factors. The foaming temperature is preferably lower than the melting point (Tmp) of the resin beads before foaming. The foaming temperature is preferably, for example, (Tmp-40)°C to (Tmp-10)°C, more preferably (Tmp-30)°C to (Tmp-10)°C, even more preferably (Tmp-20)°C to (Tmp-15)°C, and most preferably (Tmp-19)°C to (Tmp-16)°C. When the foaming temperature is (Tmp-40)°C or higher, expanded beads with a suitable density tend to be obtained. On the other hand, when the foaming temperature is Tmp°C or lower, there is no risk of hydrolysis of the resin beads occurring in the container.

[0095] In one embodiment of the present invention, the foaming temperature preferably falls within the above-mentioned temperature range and is 130.0°C or higher. When the foaming temperature falls within the above-mentioned temperature range and is 130.0°C or higher, expanded beads with good bulk density can be obtained and the holding time can be shortened. Components other than P3HA contained in the resin particles (e.g., additives) have almost no effect on the melting point of the resin particles. In other words, the melting point of the resin particles can also be said to be the melting point of the P3HA contained in the resin particles.

[0096] In the temperature-pressure increasing step, the rate at which the temperature is increased to the desired foaming temperature (hereinafter sometimes referred to as the temperature increase rate) is preferably 1.0°C / min to 3.0°C / min, and more preferably 1.5°C / min to 3.0°C / min. If the temperature increase rate is 1.0°C / min or more, excellent productivity is achieved. On the other hand, if the temperature increase rate is 3.0°C / min or less, there is no risk of insufficient impregnation of the resin particles with the foaming agent and insufficient reaction of the crosslinking agent with P3HA during the temperature increase.

[0097] The expansion pressure is, for example, preferably 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), more preferably 2.5 MPa (gauge pressure) to 4.5 MPa (gauge pressure), even more preferably 3.0 MPa (gauge pressure) to 4.0 MPa (gauge pressure), even more preferably 3.1 MPa (gauge pressure) to 3.5 MPa (gauge pressure), and particularly preferably 3.2 MPa (gauge pressure) to 3.4 MPa (gauge pressure). If the expansion pressure is 1.0 MPa (gauge pressure) or more, expanded beads with a suitable density can be obtained.

[0098] In the holding step, the time (holding time) for holding the dispersion in the container at near the foaming temperature and foaming pressure is not particularly limited. The holding time is preferably 1 minute to 120 minutes, more preferably 5 minutes to 100 minutes, even more preferably 10 minutes to 80 minutes, and particularly preferably 15 minutes to 70 minutes. When the holding time is 1 minute or longer, there is no risk of unreacted crosslinking agent remaining. On the other hand, when the holding time is 120 minutes or shorter, there is no risk of excessive hydrolysis of the P3HA contained in the resin particles.

[0099] (d) Release Step The release step is preferably carried out after the temperature-pressure increase step or the holding step. The release step allows the resin particles to expand, resulting in expanded particles.

[0100] In the releasing step, the "region under a pressure lower than the foaming pressure" refers to a "region under a pressure lower than the foaming pressure" or a "space under a pressure lower than the foaming pressure", and can also be referred to as "an atmosphere under a pressure lower than the foaming pressure". The region under a pressure lower than the foaming pressure is not particularly limited as long as it is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure.

[0101] In the discharging step, when the dispersion is discharged into a region with a pressure lower than the expansion pressure, the dispersion can be discharged through an orifice having a diameter of 1 mm to 5 mm for the purposes of adjusting the flow rate of the dispersion, reducing variations in the expansion ratio of the resulting expanded beads, etc. Furthermore, when resin particles with a relatively high melting point are used, the low-pressure region (space) can be filled with saturated water vapor for the purpose of improving the expandability.

[0102] (Two-Stage Expansion Process) In the above-described method for producing expanded beads, the expansion process alone may not always produce expanded beads with the desired apparent density. In such cases, the method may further include a second-stage expansion process in which the expanded beads obtained in the expansion process are further expanded. The second-stage expansion process is not particularly limited as long as it can produce expanded beads with an apparent density lower than that of the expanded beads obtained in the expansion process by further expanding the expanded beads obtained in the expansion process. Examples of the two-stage expansion process include: (s1) feeding the expanded beads obtained in the expansion process into a container; (s2) supplying air or an inorganic gas such as carbon dioxide into the container to increase the pressure inside the container; (s3) impregnating the expanded beads with the inorganic gas in (s2) and increasing the pressure inside the expanded beads above atmospheric pressure; and (s4) subsequently heating the expanded beads with steam or the like to further expand them to produce expanded beads with the desired apparent density. The expanded beads obtained in the two-stage expansion process are sometimes referred to as second-stage expanded beads. When a two-stage expansion step is carried out, the expansion step is sometimes referred to as a first-stage expansion step, and the expanded beads obtained in the first-stage expansion step are sometimes referred to as first-stage expanded beads.

[0103] The gel fraction of the second-stage expanded beads is preferably the same as that of the expanded beads, i.e., the description in the above section (Gel Fraction) can be appropriately applied to the gel fraction of the second-stage expanded beads.

[0104] 3. P3HA-based resin foam molded article A P3HA-based resin foam molded article according to one embodiment of the present invention is obtained by molding the above-described P3HA-based resin foam beads. The process for molding the P3HA-based resin foam beads includes a pressurizing step, a filling step, and a foam molding step. Hereinafter, the "poly(3-hydroxyalkanoate) foam molded article" will also be referred to as the "foam molded article." There are no particular limitations on the method for producing this foam molded article (i.e., the method for molding the foam beads), and known methods can be used. Examples of in-mold foam molding methods include, but are not limited to, the following (A) to (D): (A) a method in which the present expanded beads are pressurized with an inorganic gas in a container to impregnate the expanded beads with the inorganic gas, and after applying a predetermined internal pressure to the expanded beads, the expanded beads are filled into a mold and heated with steam; (B) a method in which the present expanded beads are filled into a mold, compressed so as to reduce the volume within the mold by 10% to 75%, and heated with steam; (C) a method in which the present expanded beads are compressed with gas pressure and filled into a mold, and heated with steam using the recovery force of the expanded beads; (D) a method in which the present expanded beads are filled into a mold without any particular pretreatment, and heated with steam.

[0105] In the production of the present foamed molded article, the pressure of the steam used to heat the present foamed beads (hereinafter sometimes referred to as the molding pressure) varies depending on the properties of the foamed beads used, etc., and cannot be generally defined. The molding pressure is preferably 0.05 MPa to 0.30 MPa (gauge pressure), more preferably 0.08 MPa to 0.25 MPa (gauge pressure), and even more preferably 0.10 MPa to 0.20 MPa (gauge pressure).

[0106] In the method (A) of producing a foamed molded article, the inorganic gas that can be used is at least one selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc. Among these inorganic gases, air and / or carbon dioxide are preferred.

[0107] In the method (A) for producing a foamed molded article, the temperature inside the container when the inorganic gas is impregnated into the foamed particles is preferably 10°C to 90°C, more preferably 20°C to 90°C, more preferably 30°C to 90°C, and even more preferably 40°C to 90°C.

[0108] In the method (A) for producing a foamed molded article, the internal pressure of the foamed beads is preferably 0.10 MPa to 0.30 MPa (absolute pressure), more preferably 0.11 MPa to 0.25 MPa (absolute pressure), and even more preferably 0.12 MPa to 0.20 MPa (absolute pressure). The internal pressure of the foamed beads may be measured according to the measurement method described in the examples below.

[0109] The expansion ratio of the P3HA resin foam molded article obtained as described above is preferably 20 to 60 times, more preferably 23 to 50 times, and even more preferably 25 to 40 times. Within the above range, a foam molded article with a good balance between mechanical strength and light weight can be provided. For the method of calculating the expansion ratio, see the examples of this application.

[0110] The P3HA-based resin foam molded article according to one embodiment of the present invention can be used for a variety of applications, including food containers, cushioning materials for packaging, agricultural product boxes, fish boxes, and low-temperature transport containers, all of which are used in low-temperature environments.

[0111] The present invention is not limited to the above-described embodiments, and various modifications are possible within the scope of the claims. Embodiments obtained by appropriately combining the technical means disclosed in different embodiments are also included in the technical scope of the present invention.

[0112] That is, one aspect of the present invention includes the following: <1> Expanded poly(3-hydroxyalkanoate)-based resin beads obtained by expanding resin particles containing a poly(3-hydroxyalkanoate)-based resin, wherein the resin particles contain two or more types of poly(3-hydroxyalkanoate)-based resins having different constitutional unit compositions, and the expanded poly(3-hydroxyalkanoate)-based resin beads have a glass transition temperature of 2.0°C or lower. <2> The expanded poly(3-hydroxyalkanoate)-based resin beads according to <1>, wherein the resin particles contain, as the poly(3-hydroxyalkanoate)-based resin, a copolymer having 3-hydroxybutyrate units and comonomer units, and the average content of the comonomer units in 100 mol% of all repeating units in the copolymer is 6.5 to 12.0 mol%. <3> The expanded poly(3-hydroxyalkanoate)-based resin particles according to <1> or <2>, wherein the poly(3-hydroxyalkanoate)-based resin contains a copolymer having 3-hydroxybutyrate units and comonomer units, and the resin particles contain copolymer (A) having a comonomer unit content of 1.0 to 6.0 mol% and copolymer (B) having a comonomer unit content of 13.0 mol% or more. <4> The expanded poly(3-hydroxyalkanoate)-based resin particles according to <3>, wherein the proportion of copolymer (A) is 65% by weight or more relative to 100% by weight of the total of copolymer (A) and copolymer (B). <5> The expanded poly(3-hydroxyalkanoate)-based resin particles according to any one of <1> to <4>, wherein the resin particles are poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). <6> The expanded poly(3-hydroxyalkanoate) resin beads according to any one of <1> to <5>, wherein the expanded poly(3-hydroxyalkanoate) resin beads have an expansion ratio of 20 to 50. <7> The expanded poly(3-hydroxyalkanoate) resin beads according to any one of <1> to <6>, wherein the gel fraction is 65 to 90% by weight, relative to 100% by weight of the expanded poly(3-hydroxyalkanoate) resin beads.<8> The expanded poly(3-hydroxyalkanoate) resin beads according to any one of <1> to <7>, having a bulk density of 20.0 to 600.0 g / L. <9> A poly(3-hydroxyalkanoate) resin foam molded article obtained by molding the expanded poly(3-hydroxyalkanoate) resin beads according to any one of <1> to <8>.

[0113] The present invention will be described in more detail below based on examples, but the present invention is not limited to these examples.

[0114] [Materials] The materials used in the examples and comparative examples are shown below.

[0115] (Poly(3-hydroxyalkanoate)) P3HA-1: P3HA-1 was P3HB3HH (monomer ratio: 3HB / 3HH = 94.5 / 5.5 (mol% / mol%)) and was prepared according to the method described in Example 1 of WO 2019 / 142845. P3HA-2: P3HA-2 was P3HB3HH (monomer ratio: 3HB / 3HH = 98 / 2 (mol% / mol%)) and was prepared according to the method described in Example 2 of WO 2019 / 142845. P3HA-3: P3HA-3 is P3HB3HH (monomer ratio: 3HB / 3HH = 72 / 28 (mol% / mol%)) and was prepared according to the method described in Example 9 of WO 2019 / 142845.

[0116] (Nucleating agent) Pentaerythritol (Neuraizer P, manufactured by Mitsubishi Chemical Corporation) (Foaming agent) Talc (Micro Ace K1, manufactured by Nippon Talc Co., Ltd.) (Lubricant) Behenic acid amide (BNT-22H, manufactured by Nippon Fine Chemicals Co., Ltd.) Erucic acid amide (Neutron-S, manufactured by Nippon Fine Chemicals Co., Ltd.) (Blowing agent) Carbon dioxide (manufactured by Air Water Inc.) Nitrogen (manufactured by Air Water Inc.) (Crosslinking agent) 1,1-di(t-butylperoxy)cyclohexane (TBCH: Perhexa C, manufactured by NOF Corporation) (Dispersant) Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) (Dispersing aid) Sodium alkanesulfonate (Latemul PS, manufactured by Kao Corporation).

[0117] [Measurement Methods] Measurements and evaluations in the examples and comparative examples were carried out by the following methods.

[0118] (Measurement of Glass Transition Temperature) The glass transition temperatures of P3HA-based resin particles and expanded P3HA-based resin particles were measured using a differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.). The specific operating procedure is as follows: (1) 2 mg of P3HA is weighed out; (2) the temperature of the P3HA is increased from -50°C to 190°C at a heating rate of 10°C / min to melt the P3HA; (3) In the DSC curve of P3HA obtained in the process (2), the glass transition temperature is determined as the point where a line equidistant in the vertical direction from the line extending from the low-temperature baseline and the high-temperature baseline intersects with the curve representing the stepwise change in the glass transition.

[0119] (Measurement of Gel Fraction) The gel fraction of expanded P3HA resin beads was measured by the following steps (1) to (5): (1) 1 g of expanded beads and 100 ml of chloroform were placed in a 150 ml flask; (2) the mixture in the flask was heated under reflux at 62°C under atmospheric pressure for 8 hours; (3) the resulting heat-treated product was filtered using a suction filtration device equipped with a 100-mesh wire mesh; (4) the filtered product on the wire mesh was dried in an oven at 80°C under vacuum conditions for 8 hours, and the weight of the dried product, Wg (g), was measured; (5) the gel fraction was calculated using the following formula: gel fraction (wt%) = Wg / 1 × 100.

[0120] (Dynamic Test Evaluation) As a dynamic test of the P3HA-based resin foam molded body, a destructive test was carried out using ACST-200 (manufactured by Shin-ei Technology Co., Ltd.) and M130-4290 (manufactured by Kyowa Electronics Co., Ltd.) under the conditions of a drop height of 885 mm, a free fall method, a strain of 80% or more, and a sample size of 100 × 100 × 50 mm (without skin).

[0121] The destructive test was carried out as follows: (1) the sample was placed on a table, and a weight was raised to a height of 885 mm (drop height) from the sample; (2) the stopper supporting the weight was removed, and the weight was allowed to fall freely onto the sample.

[0122] The evaluation method involved preparing three samples of P3HA-based resin foam molded articles for each Example and Comparative Example, and subjecting the three prepared samples to the above-mentioned destructive test at a test temperature of -10°C. If it was confirmed that no cracks and / or crevices occurred in all three samples, the test temperature was lowered by 5°C increments and the same destructive test was repeated. The lowest temperature at which it was confirmed that no cracks and / or crevices occurred in all three samples was taken as the dynamic drop test pass temperature.

[0123] (Measurement of bulk density and calculation of expansion ratio) The bulk density of the expanded P3HA resin beads was measured by the following steps (1) to (3): (1) the weight W (g) of the expanded beads was measured; (2) the entire amount of the expanded beads having the weight W was placed in a measuring cylinder, and the volume V (L) of the expanded beads was measured; (3) the bulk density of the expanded beads was calculated using the following formula: bulk density (g / L) = W / V.

[0124] The expansion ratio of the expanded P3HA resin beads was calculated using the above bulk density according to the following formula: specific gravity of expanded P3HA resin beads (1200) / bulk density.

[0125] (DSC Peak Area (Heat of Fusion)) The DSC peak area was measured by the following steps (1) to (4): (1) Approximately 2 mg of expanded beads were weighed; (2) Using a differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.), the expanded beads were melted by increasing the temperature from 10°C to 190°C at a heating rate of 10°C / min using a differential scanning calorimeter; (3) In the DSC curve obtained in the step (2), a baseline was created by connecting the point representing the melting start temperature (80°C) with the point representing the melting end temperature with a straight line; (4) The area surrounded by the created baseline and the DSC curve was defined as the DSC peak area, and the heat calculated from the DSC peak area was defined as the heat of fusion of the expanded beads.

[0126] (Shrinkage Ratio of Foam Molded Article) The methods for measuring and evaluating the shrinkage ratio of foam molded articles were as follows (1) to (3): (1) the length t (mm) of the foam molded article in the longitudinal direction was measured; (2) the length K (mm) of the molding space of the mold used for in-mold foam molding of the foam molded article in the direction corresponding to the longitudinal direction of the foam molded article was measured; (3) the shrinkage ratio of the foam molded article was calculated according to the following formula: shrinkage ratio (%)={(K−t) / K}×100.

[0127] Example 1 <Resin Particle Production Process> A twin-screw extruder (TEM-26SX manufactured by Toshiba Machine Co., Ltd.) was used to melt-knead the P3HA-based composition. Based on 100 parts by weight of the P3HA-based resin composition, 86 parts by weight of P3HA-1, 7 parts by weight of P3HA-2, 7 parts by weight of P3HA-3, 0.10 parts by weight of talc as a cell regulator, 1.0 parts by weight of pentaerythritol as a crystal nucleating agent, and 0.50 parts by weight of behenic acid amide and 0.5 parts by weight of erucic acid amide as lubricants were weighed and dry-blended to prepare a P3HA-based composition. The prepared P3HA-based composition was fed into the twin-screw extruder, and melt-kneaded at a cylinder setting temperature of 130.0°C to 160°C (melt-kneading step). The melt-kneaded P3HA-based composition at 180°C was extruded from a die nozzle attached to the tip of the extruder. The extruded P3HA-based composition was cooled with water at 43°C and then cut to obtain cylindrical P3HA-based resin particles with a length / diameter ratio of 2.5 (particle molding step). The melting point of the obtained resin particles was 148.4°C. The glass transition temperature of the obtained resin particles was then measured using the method described above.

[0128] <Expanded Bead Manufacturing Process> 100 parts by weight of the P3HA-based resin particles obtained in the resin particle manufacturing process, 1.8 parts by weight of TBCH as a crosslinking agent, 350 parts of pure water, 1.8 parts by weight of tribasic calcium phosphate as a dispersant, and 0.15 parts by weight of sodium alkanesulfonate as a dispersing aid were supplied to a pressure vessel. The raw materials in the pressure vessel were stirred. Thereafter, the contents (dispersion) in the pressure vessel were continuously stirred until the release of the dispersion was completed.

[0129] The pressure vessel was thoroughly aerated with carbon dioxide gas to remove oxygen from the vessel. Furthermore, carbon dioxide was supplied as a blowing agent into the vessel to prepare a dispersion (dispersion step). The temperature inside the vessel was then raised to a foaming temperature of 131.0°C. Further, carbon dioxide was supplied to the vessel to raise the pressure inside the vessel to a foaming pressure of 3.3 MPa (gauge pressure) (temperature-pressure increase step). The temperature and pressure inside the vessel were then maintained near the foaming temperature and foaming pressure, respectively, for 20 minutes (holding step). After the holding step, the valve at the bottom of the vessel was opened, and the dispersion in the vessel was released to atmospheric pressure through a 3.6 mm diameter orifice to obtain P3HA-based expanded beads (release step). The dispersant and other substances adhering to the surface of the expanded beads were washed with water, and the expanded beads were then dried at 75°C. The expanded beads obtained by drying were subjected to the measurement of glass transition temperature, gel fraction, bulk density, calculation of expansion ratio, and measurement of heat of fusion by the methods described above.

[0130] <Step of manufacturing foamed molded article> The foamed beads were supplied to a pressure vessel at 80°C. With the temperature inside the pressure vessel maintained at 80°C, the foamed beads in the pressure vessel were pressurized with air until the internal pressure of the foamed beads reached 0.16 MPa (absolute pressure). The pressure vessel was cooled to room temperature, and the foamed beads inside the pressure vessel (the foamed beads to which internal pressure had been applied) were removed (pressurization step).

[0131] The mold used was a mold having a molding space of 370 mm length x 320 mm width x 80 mm thickness, mounted on a molding machine (EP-900 manufactured by DAISEN Co., Ltd.) The molding space of the mold, which had a cracking of 4.0 mm, was filled with expanded beads to which internal pressure had been applied in a pressurizing step using a filling machine (filling step).

[0132] Next, the movable mold was driven toward the fixed mold, and after the mold was completely closed, the mold was preheated with steam, further heated in one direction and in the reverse direction with steam, and then heated on both sides with steam. Through these operations, the filled foamed beads were fused to obtain a foamed molded article (foam molding process). The steam pressure during one direction heating and the reverse direction heating (steam pressure A) was 0.06 MPa (gauge pressure), and the steam pressure during the double-sided heating (steam pressure B) was 0.13 MPa (gauge pressure). The obtained foamed molded article was removed from the mold and dried at 75°C. The dried foamed molded article was subjected to dynamic testing to measure the dynamic drop test passing temperature and further to measure the shrinkage rate.

[0133] Example 2 Resin particles, expanded particles, and expanded molded articles were produced in the same manner as in Example 1, except that 80 parts by weight of P3HA-1, 10 parts by weight of P3HA-2, and 10 parts by weight of P3HA-3 were used in the melt-kneading step. The melting point of the resulting resin particles was 149.5°C. Furthermore, the glass transition temperature, gel fraction, bulk density, expansion ratio, and heat of fusion of the resulting expanded beads were measured in the same manner as in Example 1. Furthermore, the dynamic drop test pass temperature and shrinkage rate of the resulting expanded molded articles were measured in the same manner as in Example 1.

[0134] Example 3 Resin particles, expanded particles, and expanded molded articles were produced in the same manner as in Example 1, except that 60 parts by weight of P3HA-1, 20 parts by weight of P3HA-2, and 20 parts by weight of P3HA-3 were used in the melt-kneading step. The melting point of the resulting resin particles was 152.9°C. Furthermore, the glass transition temperature, gel fraction, bulk density, expansion ratio, and heat of fusion of the resulting expanded beads were measured in the same manner as in Example 1. Furthermore, the dynamic drop test pass temperature and shrinkage rate of the resulting expanded molded articles were measured in the same manner as in Example 1.

[0135] Example 4 Resin particles, expanded particles, and expanded molded articles were produced in the same manner as in Example 1, except that 40 parts by weight of P3HA-1, 30 parts by weight of P3HA-2, and 30 parts by weight of P3HA-3 were used in the melt-kneading step. The melting point of the resulting resin particles was 155.0°C. Furthermore, the glass transition temperature, gel fraction, bulk density, expansion ratio, and heat of fusion of the resulting expanded beads were measured in the same manner as in Example 1. Furthermore, the dynamic drop test pass temperature and shrinkage rate of the resulting expanded molded articles were measured in the same manner as in Example 1.

[0136] Comparative Example 1 Resin particles, expanded particles, and foamed molded articles were produced in the same manner as in Example 1, except that 100 parts by weight of P3HA-1 was used in the melt-kneading step, and neither P3HA-2 nor P3HA-3 was used. The melting point of the resulting resin particles was 145.3°C. Furthermore, the glass transition temperature, gel fraction, bulk density, expansion ratio, and heat of fusion of the resulting expanded beads were measured in the same manner as in Example 1. Furthermore, the dynamic drop test pass temperature and shrinkage rate of the resulting foamed molded article were measured in the same manner as in Example 1.

[0137] [Evaluation Results] Table 1 shows the results of measuring the glass transition temperature, gel fraction, bulk density, expansion ratio, and heat of fusion of the P3HA-based resin particles in the examples and comparative examples, the results of measuring the glass transition temperature of the expanded P3HA-based resin beads, and the results of dynamic test evaluation and shrinkage measurement of the P3HA-based resin foam molded articles.

[0138] It was confirmed that the glass transition temperature of both the resin particles and the expanded particles decreases as the amount of P3HA-3 used increases and the 3HH ratio increases. It was also confirmed that the dynamic drop test pass temperature of the expanded molded article tends to decrease as the glass transition temperature decreases. On the other hand, it was confirmed that when the number of parts by weight of P3HA-3 used exceeds about 20 parts by weight, the shrinkage rate of the expanded molded article tends to increase, and the performance of the expanded molded article decreases. Furthermore, it was confirmed that the dynamic drop test pass temperature of the expanded molded article decreases when the expansion temperature is between (Tmp-40)°C and Tmp°C and is 130.0°C or higher.

[0139] Specifically, it was found that if the expanded P3HA resin beads used are obtained by expanding resin particles containing a P3HA resin that includes structural units composed of two or more different compositions, and the glass transition temperature of the expanded P3HA resin beads is 2.0° C. or lower, the resulting foamed molded article will have sufficient strength when used in an extremely low temperature environment (−20° C. or lower). Furthermore, it was found that if such expanded P3HA resin beads are used, the shrinkage rate of the resulting foamed molded article will be reduced, i.e., the performance of the foamed molded article will tend to be improved.

[0140] One embodiment of the present invention can be suitably used for food containers, cushioning materials for packaging, agricultural product boxes, fish boxes, low-temperature transport containers, etc.

Claims

1. A poly(3-hydroxyalkanoate)-based resin expanded particle obtained by expanding resin particles containing a poly(3-hydroxyalkanoate)-based resin, the resin particles contain two or more types of poly(3-hydroxyalkanoate) resins having different constitutional unit compositions, The resin particles contain, as the poly(3-hydroxyalkanoate)-based resin, a copolymer having a 3-hydroxybutyrate unit and a comonomer unit, The resin particles contain a copolymer (A) having a comonomer unit content of 1.0 to 6.0 mol % and a copolymer (B) having a comonomer unit content of 13.0 mol % or more, The expanded poly(3-hydroxyalkanoate) resin particles have a glass transition temperature of 2.0° C. or lower.

2. the resin particles contain, as the poly(3-hydroxyalkanoate)-based resin, a copolymer having a 3-hydroxybutyrate unit and a comonomer unit; 2. The expanded poly(3-hydroxyalkanoate) resin particles according to claim 1, wherein the average content of the comonomer units in 100 mol % of all repeating units in the copolymer is 6.5 to 12.0 mol %.

3. The expanded poly(3-hydroxyalkanoate)-based resin particles according to claim 1 or 2, wherein the proportion of the copolymer (A) is 65% by weight or more relative to 100% by weight of the total of the copolymer (A) and the copolymer (B).

4. 3. The expanded poly(3-hydroxyalkanoate)-based resin particles according to claim 1, wherein the resin particles contain poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).

5. 3. The expanded poly(3-hydroxyalkanoate) resin beads according to claim 1, wherein the expansion ratio of the expanded poly(3-hydroxyalkanoate) resin beads is 20 to 50 times.

6. 3. The expanded poly(3-hydroxyalkanoate) resin beads according to claim 1, wherein the gel fraction is 65 to 90% by weight based on 100% by weight of the expanded poly(3-hydroxyalkanoate) resin beads.

7. 3. The expanded poly(3-hydroxyalkanoate) resin particles according to claim 1, having a bulk density of 20.0 to 600.0 g / L.

8. 3. A poly(3-hydroxyalkanoate) resin foamed article obtained by molding the expanded poly(3-hydroxyalkanoate) resin beads according to claim 1 or 2.