Method for producing poly (3-hydroxyalkanoate) -based resin foam particle

Abstract

To provide a P3HA-based resin foam particle having a high expansion ratio by using a P3HA-based resin particle having a narrow molecular weight distribution as a raw material.SOLUTION: There is provided a method for producing P3HA-based resin foam particles comprising the steps of: dispersing P3HA-based resin particles having a specific weight-average molecular weight and a molecular weight distribution of less than 2.3, an organic peroxide of a specific type and in a specific amount, and a foaming agent into an aqueous dispersion medium in a vessel; and releasing the dispersion in the vessel to a region having a lower pressure than the pressure in the vessel.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing expanded poly(3-hydroxyalkanoate) resin beads. [Background technology]

[0002] In recent years, efforts have been made to utilize biodegradable resins from the perspective of environmental considerations. One type of biodegradable resin known is poly(3-hydroxyalkanoate)-based resin (hereinafter sometimes referred to as "P3HA-based resin"), which is a resin produced by microorganisms.

[0003] As one method for utilizing P3HA-based resins, expanded beads (expanded P3HA-based resin beads) using P3HA-based resins as a base resin have been proposed, as described in Patent Documents 1 and 2. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] International Publication No. WO2019 / 146555 [Patent Document 2] International Publication No. WO2023 / 189102 Summary of the Invention [Problem to be solved by the invention]

[0005] Expanded P3HA resin beads are produced by expanding P3HA resin particles. In the course of their research, the present inventors have discovered that when expanded P3HA resin beads are produced using P3HA resin particles with a narrow molecular weight distribution as a raw material, the resulting expanded P3HA resin beads have a lower expansion ratio than when expanded P3HA resin particles with a wide molecular weight distribution are used as a raw material.

[0006] In light of the above situation, an object of one embodiment of the present invention is to provide expanded poly(3-hydroxyalkanoate) resin particles with a high expansion ratio using P3HA resin particles with a narrow molecular weight distribution as a raw material. [Means for solving the problem]

[0007] As a result of intensive research conducted by the inventors to solve the above-mentioned problems, they discovered that a method for producing expanded P3HA-based resin beads, which includes the steps of dispersing P3HA-based resin particles with a narrow molecular weight distribution in an aqueous dispersion medium together with a specific type and amount of organic peroxide and a blowing agent in a container, and releasing the dispersion liquid in the container into a region with a lower pressure than the pressure in the container, can provide expanded poly(3-hydroxyalkanoate)-based resin beads with a high expansion ratio, even when using P3HA-based resin particles with a narrow molecular weight distribution as a raw material, and have thus completed the present invention.

[0008] That is, one aspect of the present invention includes the following configuration. [1] A method for producing expanded poly(3-hydroxyalkanoate) resin particles, comprising: a dispersing step of dispersing poly(3-hydroxyalkanoate) resin particles, an organic peroxide, and a blowing agent in an aqueous dispersion medium in a container; and a releasing step of opening one end of the container and releasing the dispersion liquid in the container into a region with a lower pressure than the pressure in the container, wherein the poly(3-hydroxyalkanoate) resin particles have a weight-average molecular weight of 350,000 to 600,000 and a molecular weight distribution (weight-average molecular weight / number-average molecular weight) of less than 2.3, the amount of the organic peroxide used in the dispersing step is 1.0 to 1.8 parts by weight per 100 parts by weight of the poly(3-hydroxyalkanoate) resin particles, and the organic peroxide is one or more compounds selected from a peroxyketal compound and a peroxycarbonate compound. [2] The method for producing expanded poly(3-hydroxyalkanoate) resin beads according to [1], wherein the dispersing step further comprises a temperature increasing step of increasing the temperature in the container to 120.0°C to 140.0°C, and a holding step of holding the temperature in the container for 20 minutes or more. [3] A method for producing expanded poly(3-hydroxyalkanoate) resin particles according to [1] or [2], wherein the poly(3-hydroxyalkanoate) resin particles contain two or more types of poly(3-hydroxyalkanoate) resins each having a different weight-average molecular weight. [4] The method for producing expanded poly(3-hydroxyalkanoate) resin particles according to [2], wherein the dispersing step further includes a pressure increasing step of increasing the pressure inside the container to 1.0 MPa to 10.0 MPa (gauge pressure), and the temperature and pressure inside the container are maintained for 20 minutes or more in the holding step. [Effects of the Invention]

[0009] According to one aspect of the present invention, expanded P3HA resin particles having a high expansion ratio can be provided using P3HA resin particles having a narrow molecular weight distribution as a raw material. DETAILED DESCRIPTION OF THE INVENTION

[0010] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0011] 1. Technical Concept of the Present Invention P3HA resins are biodegradable resins that can be produced by microorganisms, and microbially produced P3HA resins are actively used from the viewpoint of carbon neutrality, etc. However, when producing P3HA resins using microorganisms, it is difficult to control the molecular weight of the P3HA resin produced due to the influence of the metabolic state of the microorganisms, etc. As a result, the molecular weight distribution of the P3HA resin produced varies greatly from production lot to production lot. For the above reasons, P3HA resins produced by microorganisms may contain P3HA resins with narrow molecular weight distributions.

[0012] The molecular weight distribution of P3HA-based resin particles is proportional to the molecular weight distribution of the P3HA-based resin contained in the P3HA-based resin particles. Therefore, P3HA-based resin particles containing a P3HA-based resin with a narrow molecular weight distribution as described above will also have a narrow molecular weight distribution. In this specification, the term "narrow molecular weight distribution" refers to a P3HA-based resin particle having a "weight-average molecular weight to number-average molecular weight ratio (weight-average molecular weight / number-average molecular weight) of less than 2.3." The term "broad molecular weight distribution" refers to a P3HA-based resin particle having a "weight-average molecular weight to number-average molecular weight ratio (weight-average molecular weight / number-average molecular weight) of 2.3 or greater."

[0013] In the course of their research into expanded P3HA resin beads, the inventors discovered that when expanded P3HA resin beads are produced using P3HA resin particles with a narrow molecular weight distribution as a raw material, the resulting expanded P3HA resin beads have a lower expansion ratio than when expanded P3HA resin particles with a wide molecular weight distribution are used as a raw material. The relationship between the molecular weight distribution of the raw P3HA resin particles and the expansion ratio of the expanded P3HA resin beads obtained by expanding the P3HA resin particles was previously unknown, making this a novel problem.

[0014] Having discovered this new problem, the inventors conducted extensive research to solve the problem and discovered that a method for producing expanded P3HA-based resin beads, which includes the steps of dispersing P3HA-based resin particles with a narrow molecular weight distribution in an aqueous dispersion medium together with a specific type and amount of organic peroxide and a blowing agent in a container, and releasing the dispersion liquid in the container into a region with a lower pressure than the pressure in the container, can provide expanded poly(3-hydroxyalkanoate)-based resin beads with a high expansion ratio, even when using P3HA-based resin particles with a narrow molecular weight distribution as a raw material, and thereby completed the present invention.

[0015] 2. Method for producing expanded P3HA resin beads A method for producing expanded P3HA-based resin beads according to one embodiment of the present invention (hereinafter sometimes referred to as "the present production method") includes a dispersing step of dispersing P3HA-based resin particles, an organic peroxide, and a blowing agent in an aqueous dispersion medium in a container, and a releasing step of opening one end of the container and releasing the dispersion in the container into a region with a lower pressure than the pressure inside the container. The poly(3-hydroxyalkanoate)-based resin particles have a weight-average molecular weight of 350,000 to 600,000 and a molecular weight distribution (weight-average molecular weight / number-average molecular weight) of less than 2.3. The amount of organic peroxide used in the dispersing step is 1.0 to 1.8 parts by weight per 100 parts by weight of the P3HA-based resin particles. The organic peroxide is at least one compound selected from the group consisting of peroxyketal compounds and peroxycarbonate compounds.

[0016] Because the present production method has the above-mentioned features, it is possible to provide expanded P3HA resin beads with a high expansion ratio while using P3HA resin beads with a narrow molecular weight distribution, i.e., P3HA resin beads with a molecular weight distribution of less than 2.3, as raw materials. In the following description, "expanded P3HA resin beads" may be referred to as "expanded beads," and "expanded P3HA resin beads according to one embodiment of the present invention (i.e., expanded beads produced by the present production method)" may be referred to as "the present expanded beads."

[0017] The materials (raw materials) used in this production method will be explained below, followed by a description of specific aspects of each step.

[0018] <2-1. Materials> (P3HA resin particles) The P3HA-based resin particles produced by this production method are resin particles that use a P3HA-based resin as a base resin. In the following description, "P3HA-based resin particles" may be referred to as "resin particles," and "P3HA-based resin particles according to one embodiment of the present invention" may be referred to as "the present resin particles."

[0019] In this specification, the term "base resin" refers to the resin that substantially constitutes the target resin particles. Furthermore, in this specification, "resin particles having a P3HA-based resin as the base resin" refers to resin particles that contain 50 wt% or more of a P3HA-based resin relative to the total weight of the resin particles (100 wt%).

[0020] The content of the P3HA resin in the resin particles is not particularly limited as long as it is 50% by weight or more based on the total weight of the resin particles (100% by weight). However, since the higher the content of the P3HA resin in the resin particles, the more biodegradable and environmentally friendly the expanded particles can be, the content is preferably 60% by weight or more, more preferably 70% by weight or more, even more preferably 80% by weight or more, even more preferably 90% by weight or more, and particularly preferably 95% by weight or more. The resin particles may be composed essentially of P3HA resin only.

[0021] (P3HA resin) In this specification, the P3HA-based resin is a polymer having a 3-hydroxyalkanoic acid repeating unit represented by the formula: [—CHR—CH—CO—O—] (wherein R is C n H 2n+1where n is an integer of 1 to 15.) as an essential repeating unit, and the polymer (resin) is intended to contain 3-hydroxyalkanoic acid repeating units in an amount of 50 mol % or more of all monomer repeating units (100 mol %). P3HA-based resins are highly biodegradable and can be produced using renewable biomass resources, making them effective in reducing environmental impact.

[0022] The P3HA resin preferably contains 3-hydroxyalkanoic acid repeating units in an amount of 60 mol % or more, and more preferably 70 mol % or more, of all monomer repeating units (100 mol %).

[0023] The P3HA resin contained in the resin particles is not particularly limited and may be a homopolymer containing the repeating unit described above, or a copolymer containing the repeating unit described above. Examples of the copolymer include copolymers of 3-hydroxybutanoic acid (hereinafter sometimes referred to as "3HB") with one or more monomers selected from the group consisting of 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, and 3-hydroxyoctadecanoic acid. Another example of the copolymer is a copolymer of 3HB and one or more monomers selected from the group consisting of 4-hydroxybutanoic acid, 4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-hydroxynonanoic acid, 4-hydroxydecanoic acid, 4-hydroxyundecanoic acid, 4-hydroxydodecanoic acid, 4-hydroxytridecanoic acid, 4-hydroxytetradecanoic acid, 4-hydroxyhexadecanoic acid, and 4-hydroxyoctadecanoic acid.

[0024] Specific examples of the P3HA-based resin contained in the resin particles include 3HB homopolymers such as poly(3-hydroxybutyrate) (sometimes referred to as "P3HB"), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (sometimes referred to as "P3HB4HB"), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), and poly(3-hydroxybutyrate-co-3-hydroxyoctadecanoate). Only one type of P3HA may be used, or two or more types may be used in combination. As used herein, "poly(X-co-Y)" refers to a copolymer containing X repeating units and Y repeating units, obtained by copolymerizing a monomer from which the X repeating units are derived with a monomer from which the Y repeating units are derived. Furthermore, during the production of a P3HA-based resin by a microorganism, a trace amount (approximately 1 mol % or less) of a monomer may be copolymerized. However, if this does not significantly affect the physical properties of the resulting P3HA, such a trace amount of monomer is not reflected in the name of the P3HA-based resin.

[0025] The P3HA resin contained in the resin particles preferably contains 3-hydroxybutanoic acid (3HB) repeating units. Furthermore, when the P3HA resin contains 3HB repeating units, from the viewpoint of a balance between flexibility and strength, the composition ratio of 3HB repeating units to repeating units other than 3HB repeating units (other repeating units) (3HB repeating units / other repeating units) of all monomer repeating units (100 mol%) is preferably 99 / 1 (mol% / mol%) to 60 / 40 (mol% / mol%), more preferably 97 / 3 (mol% / mol%) to 70 / 30 (mol% / mol%), and even more preferably 95 / 5 (mol% / mol%) to 80 / 20 (mol% / mol%). When the composition ratio of 3HB repeating units in the P3HA resin is 60 mol% or more, it is advantageous in that resin products can be provided with superior rigidity. On the other hand, when the composition ratio of 3HB repeating units in the P3HA resin is 99 mol% or less, it is advantageous in that resin products can be provided with superior flexibility. The monomer composition ratio of the P3HA resin can be measured by gas chromatography or the like (see, for example, WO 2014 / 020838).

[0026] P3HA resins can be produced by microorganisms. The first microorganism capable of producing P3HA resins was Bacillus megaterium, discovered in 1925. Other known natural microorganisms include Cupriavidus necator (formerly Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. These microorganisms accumulate P3HB within their cells.

[0027] Known microorganisms that produce P3HA resins, which are copolymers of 3HB and other hydroxyalkanoic acids, include Aeromonas caviae, which produces P3HB3HH, and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co-4-hydroxybutyrate). To increase P3HB3HH productivity, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)) is particularly preferred. In addition to the above, genetically modified microorganisms containing various P3HA synthesis-related genes may be used, or culture conditions, including the type of substrate, may be optimized depending on the P3HA resin desired.

[0028] The weight-average molecular weight of the P3HA resin contained in the present resin particles is not particularly limited, but is preferably 350,000 to 700,000, more preferably 400,000 to 650,000, and even more preferably 400,000 to 600,000, in order to provide resin particles having a suitable weight-average molecular weight. In this specification, the weight-average molecular weight of the P3HA resin is a value measured using gel permeation chromatography under the following conditions: Column: TSK-GEL GMHXL16141 manufactured by Tosoh Corporation Column temperature: 40℃ Mobile phase: chloroform Standard material: polystyrene.

[0029] (additives) The resin particles may further contain additives in addition to the P3HA-based resin. Examples of additives that may be contained in the resin particles include crosslinkers, crystal nucleating agents, cell control agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, antioxidants, UV absorbers, colorants, inorganic fillers, organic fillers, hydrolysis inhibitors, and nonionic water-soluble polymers. The resin particles may contain only one of these additives, or two or more of them. Furthermore, biodegradable additives are particularly preferred.

[0030] Examples of nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. One of these nucleating agents may be used alone, or two or more may be used in combination. When two or more nucleating agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0031] 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, and bentonite. Among these cell regulators, talc is preferred because of its particularly excellent dispersibility in P3HA-based resins. One of these cell regulators may be used alone, or two or more may be used in combination. When two or more cell regulators are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0032] Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid.

[0033] Examples of the antistatic agent include coconut oil fatty acid diethanolamide.

[0034] The content of these additives in the resin particles is not particularly limited, and can be appropriately determined by a person skilled in the art.

[0035] (Molecular weight of resin particles) The resin particles have a weight average molecular weight of 350,000 to 600,000 and a molecular weight distribution of less than 2.3.

[0036] The weight average molecular weight of the resin particles is not particularly limited as long as it is 350,000 to 600,000, but is preferably 350,000 to 550,000, more preferably 370,000 to 500,000, and even more preferably 370,000 to 480,000, since this has the advantage of being able to provide expanded particles with a higher expansion ratio and to provide expanded molded articles with high strength.

[0037] The weight-average molecular weight of resin particles is proportional to the weight-average molecular weight of the P3HA resin contained therein. To achieve the above weight-average molecular weight, the resin particles may contain only one P3HA resin having a weight-average molecular weight of 350,000 to 600,000, or may contain two or more P3HA resins having different weight-average molecular weights within the range of 350,000 to 600,000. Alternatively, the weight-average molecular weight of the resulting resin particles may be adjusted to fall within the above range by mixing P3HA resins having different weight-average molecular weights outside the range of 350,000 to 600,000, or by mixing a P3HA resin having a weight-average molecular weight outside the range of 350,000 to 600,000 with a P3HA resin having a weight-average molecular weight within the range of 350,000 to 600,000. Since it becomes easier to adjust the weight-average molecular weight of the resin particles and, as a result, the variation in the physical properties of the resulting foamed molded body can be reduced, it is preferable that the resin particles contain two or more poly(3-hydroxyalkanoate) resins each having a different weight-average molecular weight so that the weight-average molecular weight of the resin particles is within the above-mentioned range.

[0038] The molecular weight distribution of the resin particles is not particularly limited as long as it is less than 2.3, but may be 2.1 or less, or 2.0 or less. The lower limit is not particularly limited, but may be, for example, 0.1 or more, 0.5 or more, or 1.0 or more. The molecular weight distribution of the resin particles is a value calculated based on the following formula: Molecular weight distribution of the present resin particles = weight average molecular weight of the present resin particles / number average molecular weight of the present resin particles.

[0039] In this specification, the weight average molecular weight and number average molecular weight of P3HA-based resin particles, including the present resin particles, are values measured using gel permeation chromatography (Nexera GPC system manufactured by Shimadzu Corporation) under the conditions described in the examples.

[0040] <2-2. Steps that may be included in this manufacturing method> This manufacturing method includes a dispersing step of dispersing the above-mentioned resin particles, an organic peroxide, and a blowing agent in an aqueous dispersion medium in a container, and a discharging step of opening one end of the container and discharging the dispersion in the container into a region with a pressure lower than the pressure in the container.

[0041] The present manufacturing method may include at least the dispersion step and release step described above, but may also include a resin particle preparation step for preparing the present resin particles, and a two-stage expansion step for further expanding the P3HA-based resin expanded particles obtained by the release step.

[0042] Each step that may be included in this manufacturing method will be described in detail below.

[0043] (Resin particle preparation process) The present production method preferably includes a resin particle preparation step, prior to the dispersion step, in which the P3HA resin is granulated to prepare the present resin particles. The resin particle preparation step can also be considered a step of molding the P3HA resin into a shape that is easy to use for foaming. The embodiment of the resin particle preparation step is not particularly limited as long as it can produce the present resin particles, but examples include an embodiment that includes a melt-kneading step of melt-kneading a P3HA resin composition containing a P3HA resin and optional additives, and a resin particle molding step of molding the melt-kneaded P3HA resin composition into a shape that is easy to use for foaming. Below, a preferred embodiment of the resin particle preparation step will be described in more detail, taking as an example a method that includes the melt-kneading step and the resin particle molding step.

[0044] Melt-mixing process The resin particle preparation process preferably includes a melt-kneading process in which a P3HA-based resin composition containing a P3HA-based resin and optional additives is melt-kneaded. In the melt-kneading process, the temperature at which the P3HA-based resin composition is melt-kneaded (kneading temperature) cannot be generally defined because it depends on the physical properties of the P3HA-based resin (e.g., melting point, weight-average molecular weight) and the type of additives used. However, for example, a kneading temperature of 130°C to 200°C is preferred, 135°C to 180°C is more preferred, and 140°C to 160°C is even more preferred. A kneading temperature of 130°C or higher can sufficiently melt the P3HA-based resin, thereby enabling the P3HA-based resin composition to be sufficiently melt-kneaded. On the other hand, a kneading temperature of 200°C or lower can suppress thermal decomposition of the P3HA-based resin during melt-kneading.

[0045] ·Resin particle molding process The resin particle preparation step preferably includes a resin particle molding step in which the melt-kneaded P3HA-based resin composition is molded into a shape that is easily usable for foaming. The form of the resin particle molding step is not particularly limited as long as it allows the melt-kneaded P3HA-based resin composition to be molded into the desired shape. For example, when a melt-kneading device equipped with a die and a cutting device is used as the melt-kneading device in the melt-kneading step, the melt-kneaded P3HA-based resin composition can be easily molded into the desired shape by extruding the melt-kneaded P3HA-based resin composition from the die nozzle of the melt-kneading device and cutting the extruding P3HA-based resin composition with the built-in cutting device simultaneously with or after extruding. The shape into which the P3HA-based resin composition is molded in the resin particle molding step, in other words, the shape of the resin particles (present resin particles) obtained in the resin particle preparation step, is not particularly limited, but cylindrical, elliptical, spherical, cubic, rectangular, etc. are preferred because they are easily usable for foaming.

[0046] In the resin particle molding step, the P3HA resin composition extruded from the die nozzle may be cooled. When the P3HA resin composition extruded from the die nozzle is cooled, molding (cutting) may be performed simultaneously with cooling of the P3HA resin composition, or molding (cutting) of the P3HA resin composition after cooling may be performed.

[0047] (Dispersion process) This production method includes a dispersion step in which the resin particles, an organic peroxide, and a blowing agent are dispersed in an aqueous dispersion medium in a container. In addition to the above-mentioned substances, if necessary, a dispersant, a crosslinking aid, a dispersion aid, and / or a plasticizer may also be dispersed in the aqueous dispersion medium during the dispersion step. The dispersion step can also be considered a process for preparing a dispersion in a container in which the resin particles, the organic peroxide, the blowing agent, and if necessary, the dispersant, the crosslinking aid, the dispersion aid, and / or a plasticizer are dispersed. The organic peroxide, the blowing agent, and other optional dispersing substances used in the dispersion step may be consumed in the dispersion by reaction with the P3HA-based resin in the resin particles or may be impregnated into the resin particles, thereby disappearing from the aqueous dispersion medium.

[0048] The vessel used in the dispersion step is not particularly limited, but is preferably one that can withstand the foaming temperature and foaming pressure described below, for example, a pressure-resistant vessel.

[0049] The aqueous dispersion medium used in the dispersion step is not particularly limited as long as it can uniformly disperse at least the resin particles, organic peroxide, and blowing agent. From the viewpoint of enabling stable production of expanded particles, it is preferable to use pure water or ultrapure water such as RO water (water purified by reverse osmosis membrane), distilled water, deionized water (water purified by ion exchange resin), etc. Alternatively, tap water and / or industrial water can be used as the aqueous dispersion medium.

[0050] In the dispersion process, the resin particles and an organic peroxide are dispersed in an aqueous dispersion medium, and the organic peroxide is impregnated into the resin particles and reacted with them, thereby directly bonding the molecular chains of the P3HA resin in the resin particles (without going through a structure derived from a crosslinking agent) to form a crosslinked structure. Therefore, the organic peroxide can also be considered a crosslinking agent.

[0051] The organic peroxide used in the dispersion process is one or more compounds selected from peroxyketal compounds and peroxycarbonate compounds. The use of such organic peroxides in the dispersion process makes it possible to produce expanded particles with a high expansion ratio, even when using the P3HA-based resin particles, which have a narrow molecular weight distribution, as the raw material. Another advantage is that no harmful substances (such as benzene in the case of benzoyl peroxide) are generated during the reaction with benzoyl peroxide, thereby reducing the environmental impact.

[0052] Examples of peroxyketal compounds that can be used in the dispersion step include 1,1-di(t-butylperoxy)cyclohexane (1-hour half-life temperature: 111.1°C), 2,2-di(t-butylperoxy)butane (1-hour half-life temperature: 121.7°C), n-butyl-4,4-di(t-butylperoxy)valerate (1-hour half-life temperature: 126.5°C), 2,2-di(4,4-di(t-butylperoxy)cyclohexyl)propane (1-hour half-life temperature: 114.0°C), and 1,1-di(t-hexyperoxy)cyclohexane (1-hour half-life temperature: 107.3°C). These peroxyketal compounds may be used alone or in combination with two or more. Furthermore, these peroxyketal compounds may be used in combination with one or more peroxycarbonate compounds.

[0053] Examples of peroxycarbonate compounds that can be used in the dispersion step include t-butylperoxy-2-ethylhexyl monocarbonate (one-hour half-life temperature: 121° C.), t-butylperoxyisopropyl monocarbonate (one-hour half-life temperature: 118° C.), t-amylperoxyisopropyl monocarbonate (one-hour half-life temperature: 115° C.), and t-amylperoxy-2-ethylhexyl monocarbonate (one-hour half-life temperature: 117° C.). Of these peroxycarbonate compounds, one type may be used alone, or two or more types may be used in combination.

[0054] Among the above organic peroxides, organic peroxides having a one-hour half-life temperature of 90°C to 160°C are preferred, and organic peroxides having a one-hour half-life temperature of 105°C to 125°C are more preferred, as they have the advantage of being able to rapidly proceed with the crosslinking reaction near the softening temperature of the resin particles.

[0055] The amount of organic peroxide used in the dispersion step is 1.0 to 1.8 parts by weight, more preferably 1.1 to 1.7 parts by weight, and even more preferably 1.2 to 1.6 parts by weight, per 100 parts by weight of the resin particles. By using an organic peroxide in the amount within the above range, expanded particles containing a sufficiently crosslinked P3HA-based resin can be obtained, and expanded particles with a low content of substances that cause mold contamination during molding (e.g., calcium phosphate (dispersant) etc.) can be provided. Note that the "amount used" in the dispersion step means "the amount dispersed in the above-mentioned aqueous dispersion medium."

[0056] The blowing agent used in the dispersion step is not particularly limited, but examples thereof 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. When two or more blowing agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0057] The amount of the 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 the resin particles.

[0058] In the dispersion step, it is preferable to further use a dispersant. The use of a dispersant has the advantage of suppressing mutual adhesion of the resin particles and enabling stable production of expanded particles. 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. One of these dispersants may be used alone, or two or more may be used in combination. Furthermore, when two or more dispersants are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0059] When a dispersant is used, the amount of the dispersant used in the dispersion step is not particularly limited, but is preferably 0.01 to 3.00 parts by weight, more preferably 0.03 to 1.50 parts by weight, and even more preferably 0.05 to 1.00 parts by weight, relative to 100 parts by weight of the resin particles. If the amount of the dispersant used is within the above range, the dispersant will exhibit sufficient effects as a dispersant without impairing the effects of the present invention.

[0060] In the dispersion step, a dispersing aid may be used to further improve the effect of suppressing mutual adhesion between resin particles. Examples of dispersing aids include anionic surfactants such as sodium alkane sulfonate, sodium alkylbenzene sulfonate, and sodium α-olefin sulfonate. 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.

[0061] When a dispersing aid is used, the amount of the dispersing aid used in the dispersion step is not particularly limited, but is preferably 0.01 to 3.00 parts by weight, more preferably 0.03 to 1.50 parts by weight, and even more preferably 0.05 to 1.00 parts by weight, relative to 100 parts by weight of the resin particles. If the amount of the dispersing aid used is within the above range, the effect of the present invention is not impaired and the dispersing aid exerts a sufficient effect.

[0062] In the dispersion step, a crosslinking aid may be used to improve the crosslinking efficiency of the P3HA resin. Examples of crosslinking aids include compounds having at least one unsaturated bond in the molecule. Among these compounds, allyl esters, acrylic esters, methacrylic esters, divinyl compounds, and the like are particularly preferred as crosslinking aids. One of these crosslinking aids may be used alone, or two or more may be used in combination. When two or more crosslinking aids are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0063] When a crosslinking aid is used, the amount of the crosslinking aid used in the dispersion step is not particularly limited, but is preferably 0.01 to 3.00 parts by weight, more preferably 0.03 to 1.50 parts by weight, and even more preferably 0.05 to 1.00 parts by weight, relative to 100 parts by weight of the resin particles. If the amount of the crosslinking aid used is within the above range, the crosslinking aid will exert a sufficient effect without impairing the effects of the present invention.

[0064] In the dispersion step, when the resin particles are impregnated with and reacted with an organic peroxide 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 crosslinking efficiency. 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 an inorganic gas such as carbon dioxide or nitrogen, and evacuating the gas in the container.

[0065] A plasticizer may be used in the dispersion process. Examples of plasticizers that can be used in the dispersion process include glycerin ester compounds such as glycerin diacetomonolaurate, citrate ester compounds such as acetyl tributyl citrate, sebacate compounds such as dibutyl sebacate, adipate compounds, polyether ester compounds, benzoate ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds such as benzyl methyl diethylene glycol adipate. Among these, glycerin ester compounds, citrate ester compounds, sebacate ester compounds, and dibasic acid ester compounds are preferred because of their excellent plasticizing effect on aliphatic polyester resins. One of these plasticizers may be used alone, or two or more may be used in combination. When two or more plasticizers are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0066] When a plasticizer is used, the amount of the plasticizer used is not particularly limited, but is preferably 0.01 to 4 parts by weight per 100 parts by weight of the resin particles. By using the plasticizer in the above amount, expanded beads that can provide expanded molded articles with good strength can be produced.

[0067] Heating process, pressure rising process and holding process The dispersion step preferably includes a temperature-raising step of raising the temperature inside a container containing a dispersion liquid containing the resin particles, an organic peroxide, and a foaming agent to a constant temperature (foaming temperature), a pressure-raising step of raising the pressure inside the container to a constant pressure (foaming pressure), and / or a holding step of maintaining the temperature and pressure inside the container at a constant temperature and / or constant pressure (i.e., the foaming temperature and / or foaming pressure).

[0068] The foaming temperature in the temperature-raising step is not particularly limited, but is preferably 120.0°C to 140.0°C, more preferably 125.0°C to 135.0°C, and even more preferably 130.0°C to 133.0°C, because this allows the crosslinking reaction by the organic peroxide to proceed quickly and also allows hydrolysis of P3HA to be suppressed during the foaming process. Furthermore, the rate at which the temperature is raised to the desired foaming temperature in the temperature-raising step is not particularly limited, but may be, for example, 1.0°C / min to 3.0°C / min.

[0069] The expansion pressure in the pressure increasing step is not particularly limited, but is preferably 1.0 MPa to 10.0 MPa (gauge pressure), more preferably 2.0 MPa to 5.0 MPa (gauge pressure), and even more preferably 2.5 MPa to 4.0 MPa, since expanded beads with a higher expansion ratio can be provided.

[0070] In the holding step, the time for which the temperature and pressure in the container are held at the foaming temperature and / or foaming pressure is not particularly limited, but is preferably 20 minutes or more, more preferably 30 minutes or more, from the viewpoint of fully exerting the desired effects of the temperature and pressure increase. In the holding step, (1) when only the temperature increase step is performed, it is preferable to hold at least the temperature in the container constant, (2) when only the pressure increase step is performed, it is preferable to hold at least the pressure in the container constant, and (3) when both the temperature increase step and the pressure increase step are performed, it is preferable to hold both the temperature and pressure in the container constant.

[0071] In one embodiment of the present invention, the dispersion step preferably includes a temperature-raising step of raising the temperature inside the container to 120°C to 140°C and a holding step of maintaining the container at that temperature for 20 minutes or more, because this allows the crosslinking reaction by the organic peroxide to proceed more quickly and further suppresses hydrolysis of P3HA during the foaming process. It is more preferable that the dispersion step includes a temperature-raising step of raising the temperature inside the container to 120°C to 140°C, a pressure-raising step of raising the pressure inside the container to 1.0 MPa to 10.0 MPa (gauge pressure), and a holding step of maintaining the container at that temperature and pressure for 20 minutes or more.

[0072] (Release process) The present production method includes a dispersing step in which the resin particles, an organic peroxide, and a blowing agent are dispersed, and preferably further includes a releasing step in which one end of a container containing the dispersion that has been subjected to the temperature-raising, pressure-raising, and / or holding steps is opened and the dispersion in the container is released into a region with a pressure lower than that in the container. By carrying out the releasing step, the resin particles can be expanded, resulting in expanded particles.

[0073] In the releasing step, the "region under a pressure lower than the pressure inside the container" refers to "a region under a pressure lower than the pressure inside the container" or "a space under a pressure lower than the pressure inside the container", and can also be referred to as "an atmosphere under a pressure lower than the pressure inside the container". The region under a pressure lower than the pressure inside the container is not particularly limited as long as it is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure. Furthermore, when a temperature-pressure increasing step is performed, the "pressure inside the container" in the releasing step can also be referred to as the "foaming pressure".

[0074] In the release step, the pressure in the region lower than the pressure inside the container is not particularly limited as long as it is a region lower than the pressure inside the container, and in particular, when a pressure increase step is carried out in the dispersion step, the pressure in the region lower than the pressure inside the container may be atmospheric pressure.

[0075] In the discharging step, when discharging the dispersion into a region with a lower pressure than the pressure inside the container, it is preferable to discharge the dispersion through an orifice with a diameter of 1 mm to 5 mm, since this allows the flow rate of the dispersion to be adjusted and allows homogeneous expanded beads to be obtained.

[0076] In the releasing step, the resulting expanded beads may be washed with a detergent. Examples of detergents include warm water and sodium hexametaphosphate. Washing the expanded beads allows the amount of dispersant and other components adhering to the surface of the expanded beads to be adjusted.

[0077] (Two-stage foaming process) From the viewpoint of obtaining expanded beads with a higher expansion ratio, the present production method may include a second-stage expansion step in which the expanded beads obtained through the series of steps from the dispersing step to the discharging step are further expanded. When the second-stage expansion step is performed, the series of steps including the dispersing step to the discharging step is sometimes referred to as a first-stage expansion step, and the expanded beads obtained through the first-stage expansion step are sometimes referred to as first-stage expanded beads.

[0078] The second-stage expansion process can be carried out, for example, in the following manner: (1) the first-stage expanded particles obtained in the first-stage expansion process are fed into a container; (2) air or an inorganic gas such as carbon dioxide is fed into the container to increase the pressure inside the container; (3) the inorganic gas is impregnated into the first-stage expanded particles by the process (2), and the pressure inside the first-stage expanded particles is increased above atmospheric pressure; (4) the inorganic gas-impregnated first-stage expanded particles are then heated with steam or the like to further expand them, thereby obtaining expanded particles with a higher expansion ratio.

[0079] When expanded beads having a sufficiently high expansion ratio are obtained by a series of steps including the dispersing step to the releasing step, the second-stage expansion step may or may not be carried out.

[0080] <2-3. Foam particles> The present expanded beads are expanded beads produced by the present production method. The physical properties and uses of the present expanded beads will be described in detail below.

[0081] (Physical properties of expanded beads) Foaming ratio The expansion ratio of the expanded beads is not particularly limited, but is preferably 15 times or more, more preferably 15.5 times or more, and even more preferably 16 times or more. An expansion ratio of 15 times or more means that the expanded beads have a sufficiently high expansion ratio. The higher the expansion ratio of the expanded beads, the more preferable it is, and although there is no particular upper limit, it can be, for example, 25 times or less. In this specification, the expansion ratio of the expanded beads is a value measured by the method described in the examples.

[0082] High temperature melting heat The high-temperature heat of fusion of the expanded beads is not limited, but is preferably 0.1 J / g to 20.0 J / g, more preferably 0.3 J / g to 15.0 J / g, and even more preferably 0.5 J / g to 10.0 J / g. When the high-temperature heat of fusion of the expanded beads is within the above range, it has the advantage of being able to provide a foamed molded article with excellent surface properties. The high-temperature heat of fusion of the expanded beads can be adjusted by adjusting the foaming conditions (particularly the foaming temperature, foaming pressure, and holding time). In this specification, the high-temperature heat of fusion of the expanded beads is a value measured by the method described in the Examples.

[0083] Calcium phosphate content The calcium phosphate content of the present expanded beads is not particularly limited, but is preferably 1500 ppm or less, more preferably 1000 ppm or less, from the viewpoint of suppressing mold contamination during molding. Because the present expanded beads are produced using one or more organic peroxides selected from peroxyketal compounds and peroxycarbonate compounds, even when a substance containing calcium phosphate is used in the dispersion step, the calcium phosphate content of the expanded beads can be kept at 1500 ppm or less, resulting in expanded beads that cause less mold contamination during molding. In this specification, the calcium phosphate content of the expanded beads is a value measured by the method described in the Examples.

[0084] (foam molded body) The present expanded beads can be molded by a known method to obtain a foamed molded article. That is, in one embodiment of the present invention, there is provided a foamed molded article obtained by molding the present expanded beads.

[0085] (Uses of foam particles) The expanded beads and foamed molded articles obtained by molding the expanded beads can be suitably used in a variety of fields, including packaging cushioning materials (e.g., cushioning materials for packaging home appliances such as refrigerators, freezers, air conditioner bodies and their outdoor units, washing machines, air purifiers, humidifiers, rice cookers, microwave ovens, ovens, toasters, fans, and storage battery units; and cushioning materials for packaging automotive items such as transmissions, roofs, hoods, doors, batteries, and engines), automotive components (e.g., bumper cores, headrests, luggage boxes, tool boxes, floor spacers, seat cores, child seat cores, sun visor cores, and knee pads), heat insulating materials (e.g., containers for constant temperature storage and containers for constant temperature transportation), casting models, agricultural product boxes, fish boxes, building materials, and civil engineering materials. [Example]

[0086] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0087] 〔material〕 The substances used in the examples and comparative examples are shown below.

[0088] (Poly(3-hydroxyalkanoate)) P3HA-1: P3HB3HH (monomer ratio: 3HB / 3HH = 94.5 / 5.5 (mol% / mol%), melting point: 145.0°C, Mw = 487,000, Mw / Mn = 2.3) P3HA-2: P3HB3HH (monomer ratio: 3HB / 3HH = 94.5 / 5.5 (mol% / mol%), melting point: 144.7°C, Mw = 416,000, Mw / Mn = 1.8) P3HA-3:P3HB3HH (monomer ratio 3HB / 3HH = 94.4 / 5.6 (mol% / mol%), melting point 144.4°C, Mw = 500,000, Mw / Mn = 2.5) P3HA-4: P3HB3HH (monomer ratio: 3HB / 3HH = 94.5 / 5.5 (mol% / mol%), melting point 144.4°C, Mw = 384,000, Mw / Mn = 2.2) P3HA-5: P3HB3HH (monomer ratio 3HB / 3HH = 94.4 / 5.6 (mol% / mol%), melting point 145.8°C, Mw = 470,000, Mw / Mn = 1.8) P3HA-6: P3HB3HH (monomer ratio: 3HB / 3HH = 94.5 / 5.5 (mol% / mol%), melting point 146.2°C, Mw = 517,000, Mw / Mn = 2.5) (nucleating agent) Pentaerythritol (Mitsubishi Chemical Corporation, NeuRizer P) (lubricant) Erucic acid amide (Neutron S, manufactured by Nippon Fine Chemical Co., Ltd.) Behenamide (Nippon Fine Chemical Co., Ltd., BNT-22H) (organic peroxide) 1,1-Di(t-butylperoxy)cyclohexane (TBCH: NOF Corporation, Perhexa C, 1-hour half-life temperature: 111.1°C) (Foam adjuster) Talc (Micro Ace K-1 manufactured by Nippon Talc Co., Ltd.) (foaming agent) Carbon dioxide (manufactured by Air Water Inc.) (dispersant) Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) (Dispersion aid) Sodium alkanesulfonate (Latemul PS manufactured by Kao Corporation) [Measurement method] In the examples and comparative examples, the methods for measuring the various physical properties were as follows.

[0089] (Measurement of the melting point of resin particles) The melting point of the resin particles was measured using a differential scanning calorimeter (DSC7200 manufactured by Seiko Instruments Inc.) The specific operating procedures were as follows (1) to (3): (1) 4.5 mg to 5.5 mg of resin particles were weighed out; (2) the temperature of the weighed resin particles was increased from 10.0°C to 190.0°C at a heating rate of 10.0°C / min to melt the resin particles; (3) the temperature of the highest melting peak in the DSC curve obtained in the process (2) was determined as the melting point of the resin particles.

[0090] (Measurement of weight average molecular weight (Mw), number average molecular weight (Mn) and molecular weight distribution (Mw / Mn) of resin particles) The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the resin particles were measured by gel permeation chromatography (Nexera GPC system manufactured by Shimadzu Corporation). Specific measurement conditions were as follows: 2 mg of resin particles were weighed and dissolved in 2 mL of chloroform at 40°C. The sample was a solution prepared by dissolving 2 mg of resin particles in 2 mL of chloroform at 40°C. The column used was a TSK-GEL GMHXL16141 manufactured by Tosoh Corporation, the column temperature was 40°C, the mobile phase was chloroform, and the standard substance was polystyrene. Based on the weight-average molecular weight (Mw) and number-average molecular weight (Mn) of the resin particles measured under the above conditions, the molecular weight distribution of the resin particles was calculated according to the following formula: Molecular weight distribution of resin particles (Mw / Mn) = (weight average molecular weight of resin particles (Mw) / number average molecular weight of resin particles (Mn)).

[0091] (Measurement of expansion ratio of expanded beads) The expansion ratio of the expanded beads was measured as follows (1) to (3): (1) A measuring cylinder containing ethanol was prepared, and expanded beads with a weight W (g) were submerged in the ethanol; (2) The volume of the expanded beads with the weight W (g), which was read based on the rise in the liquid level of the ethanol, was determined as V (cm 3 (3) The expansion ratio of the expanded beads was calculated using the following formula: Expansion ratio of expanded beads (times) = specific gravity (g / cm) of resin particles used as raw material for the expanded beads to be measured 3 ) / (W / V). In the above formula, the specific gravity of the resin particles is a value measured by the underwater displacement method using an automatic pycnometer (DSG-1 manufactured by Toyo Seiki Seisaku-sho, Ltd.) in accordance with JIS K7112.

[0092] (Measurement of the heat of fusion on the high temperature side of the expanded beads) The heat of fusion of the expanded beads at high temperatures was measured using a differential scanning calorimeter (DSC7200 manufactured by Seiko Instruments Inc.) The specific operating procedures were as follows (1) to (3): (1) 4.5 mg to 5.5 mg of resin particles were weighed out; (2) the temperature of the weighed resin particles was increased from 10.0°C to 190.0°C at a heating rate of 10.0°C / min to melt the resin particles; (3) in the DSC curve obtained in the process (2), the heat of the highest melting peak was taken as the heat of fusion of the expanded beads at high temperatures.

[0093] (Measurement of calcium phosphate content in foamed beads) The calcium phosphate content of the expanded beads was measured by measuring the absorbance at a wavelength of 410 nm using an ultraviolet-visible spectrophotometer (UV-1280 manufactured by Shimadzu Corporation). The specific operating procedures were as follows (1) to (4): (1) A solution (liquid A) was prepared by dissolving 2.240 g of ammonium metavanadate in 500 mL of pure water, and a solution (liquid B) was prepared by dissolving 54.0 g of ammonium molybdate in 400 mL of pure water; (2) A solution was further prepared by mixing 250 mL of nitric acid (concentration 69 to 70 wt%), 250 mL of liquid A, 200 mL of liquid B, and 300 mL of pure water, and this was used as the color developing solution; (3) 0.5 g of expanded particles was weighed, and 50 mL of the above color developing solution was added. The mixture was shaken for at least 1 minute and then allowed to stand, and the supernatant was used as the sample solution; (4) The absorbance (wavelength 410 nm) of the sample solution obtained in (3) was measured, and the calcium phosphate content of the target expanded particles was calculated based on the measured absorbance and a standard curve using calcium phosphate solutions of known concentrations.

[0094] Example 1 (Resin particle preparation process) A P3HA-based composition was prepared by weighing and dry-blending 100 parts by weight of P3HA-1, 1.0 part by weight of pentaerythritol as a nucleating agent, 0.50 parts by weight of erucamide and 0.50 parts by weight of behenamide as lubricants, and 0.10 parts by weight of talc. The resulting P3HA-based composition was fed into a twin-screw extruder (TEM-26SX, manufactured by Toshiba Machine Co., Ltd.), and melt-kneaded at a cylinder temperature of 140 to 145°C (melt-kneading step). The melt-kneaded P3HA-based composition at 160°C was extruded from the nozzle of a die 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 resin particles weighing 1.6 mg each and having a length / diameter ratio of 1.8 (resin particle molding step). The weight-average molecular weight and molecular weight distribution of the resulting resin particles were measured. The results are shown in Table 1.

[0095] (Dispersion process) 100 parts by weight of the resin particles obtained in the above (resin particle preparation step), 1.3 parts by weight of TBCH as an organic peroxide, 378 parts by weight 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. Carbon dioxide was introduced into the pressure vessel and thoroughly aerated to remove oxygen from the pressure vessel. Furthermore, carbon dioxide was supplied as a foaming agent to the pressure vessel and dispersed in the dispersion to prepare a dispersion (dispersion step).

[0096] (Temperature increase step, pressure increase step and holding step) The temperature inside the pressure vessel was raised to a foaming temperature of 131.3°C (heating step). Carbon dioxide was then supplied to the pressure vessel to raise the pressure inside the pressure vessel to a foaming pressure of 3.2 MPa (gauge pressure) (pressure raising step). The temperature and pressure inside the pressure vessel were maintained at approximately the foaming temperature and foaming pressure, respectively, for 30 minutes (maintenance step).

[0097] (Release process) After the holding step, the valve at the bottom of the pressure vessel was opened, and the dispersion liquid in the pressure vessel was released to atmospheric pressure through a 3.6 mm diameter orifice, yielding expanded beads. The dispersant and other materials adhering to the surface of the resulting expanded beads were washed with water for 30 seconds, and then dried at 75°C. The resulting expanded beads had a length / diameter ratio of 1.0 and a cylindrical shape. After washing and drying, the expanded beads were measured for expansion ratio, high-temperature heat of fusion, and calcium phosphate content. The results are shown in Table 1.

[0098] Example 2 Resin particles and expanded particles were produced in the same manner as in Example 1, except that TBCH was used in an amount of 1.4 parts by weight, and the physical properties were measured. The results are shown in Table 1.

[0099] Example 3 Resin particles and expanded particles were produced in the same manner as in Example 1, except that P3HA-1 was changed to P3HA-2, TBCH was used at 1.5 parts by weight, and the expansion temperature was set at 130.6° C., and the physical properties were measured. The results are shown in Table 1.

[0100] Example 4 Resin particles and expanded particles were produced in the same manner as in Example 1, except that P3HA-1 was changed to P3HA-2, TBCH was used at 1.2 parts by weight, and the expansion temperature was set at 130.6° C., and the physical properties were measured. The results are shown in Table 1.

[0101] Example 5 Resin particles and expanded particles were produced in the same manner as in Example 1, except that a mixture of 80 parts by weight of P3HA-3 and 20 parts by weight of P3HA-4 (total 100 parts by weight) was used instead of P3HA-1, 1.3 parts by weight of TBCH was used, and the foaming temperature was set to 131.4°C, and the physical properties were measured. The results are shown in Table 1.

[0102] Comparative Example 1 Resin particles and expanded particles were produced in the same manner as in Example 1, except that the amount of TBCH was 2.0 parts by weight and the expansion temperature was 129.5° C., and the physical properties were measured. The results are shown in Table 1.

[0103] Comparative Example 2 Resin particles and expanded particles were produced in the same manner as in Example 1, except that P3HA-1 was changed to P3HA-2, TBCH was used at 2.3 parts by weight, and the expansion temperature was set at 130.0° C., and the physical properties were measured. The results are shown in Table 1.

[0104] Comparative Example 3 Resin particles and expanded particles were produced in the same manner as in Example 1, except that P3HA-1 was changed to P3HA-5, TBCH was used at 1.9 parts by weight, and the expansion temperature was set at 131.0°C, and the physical properties were measured. The results are shown in Table 1.

[0105] Comparative Example 4 Resin particles and expanded particles were produced in the same manner as in Example 1, except that a mixture of 80 parts by weight of P3HA-3 and 20 parts by weight of P3HA-4 (100 parts by weight in total) was used instead of P3HA-1, 2.2 parts by weight of TBCH was used, and the foaming temperature was set to 129.5°C, and the physical properties were measured. The results are shown in Table 1.

[0106] [Reference example 1] Resin particles and expanded particles were produced in the same manner as in Example 1, except that P3HA-1 was changed to P3HA-6, TBCH was used at 2.0 parts by weight, and the expansion temperature was set at 130.0° C., and the physical properties were measured. The results are shown in Table 1.

[0107] [Table 1]

[0108] As is clear from Table 1, the expanded beads of Examples 1 to 5, which were produced using a specified amount of TBCH (a peroxyketal compound) as an organic peroxide, had excellent expansion ratios exceeding 15 times, despite being made from resin particles with a narrow molecular weight distribution (a molecular weight distribution of less than 2.3), which is usually difficult to expand at a high expansion ratio. On the other hand, the expanded beads of Comparative Examples 1 to 4, which were produced using an amount of TBCH (a peroxyketal compound) exceeding the specified range, had poor expansion ratios. This shows that in order to provide expanded beads with a high expansion ratio using resin particles with a narrow molecular weight distribution as a raw material, it is necessary to use a specific organic peroxide in a specific amount.

[0109] Furthermore, the results of Reference Example 1 show that resin particles with a wide molecular weight distribution (molecular weight distribution of 2.3 or more) can produce expanded particles with a high expansion ratio even when TBCH is used in an amount exceeding the specified range. This also shows that the problem of the present invention does not occur when resin particles with a wide molecular weight distribution are used. In other words, the problem of the present invention is unique to the use of resin particles with a narrow molecular weight distribution as a raw material. [Industrial Applicability]

[0110] The expanded beads produced according to one embodiment of the present invention can be suitably used in a variety of fields, including cushioning materials for packaging (e.g., cushioning materials for packaging home appliances such as refrigerators, freezers, air conditioner bodies and their outdoor units, washing machines, air purifiers, humidifiers, rice cookers, microwave ovens, ovens, toasters, electric fans, and storage battery units; and cushioning materials for packaging automobile parts such as transmissions, roofs, hoods, doors, batteries, and engines), automobile components (e.g., bumper cores, headrests, luggage boxes, tool boxes, floor spacers, seat cores, child car seat cores, sun visor cores, and knee pads), heat insulating materials (e.g., containers for constant temperature storage and containers for constant temperature transportation), casting models, agricultural product boxes, fish boxes, building materials, and civil engineering materials.

Claims

1. a dispersing step of dispersing poly(3-hydroxyalkanoate) resin particles, an organic peroxide, and a blowing agent in an aqueous dispersion medium in a container; a discharging step of opening one end of the container and discharging the dispersion liquid in the container into a region having a pressure lower than the pressure inside the container, the poly(3-hydroxyalkanoate) resin particles have a weight-average molecular weight of 350,000 to 600,000 and a molecular weight distribution (weight-average molecular weight / number-average molecular weight) of less than 2.3; the amount of the organic peroxide used in the dispersing step is 1.0 parts by weight to 1.8 parts by weight with respect to 100 parts by weight of the poly(3-hydroxyalkanoate)-based resin particles, The method for producing expanded poly(3-hydroxyalkanoate) resin particles, wherein the organic peroxide is at least one compound selected from the group consisting of peroxyketal compounds and peroxycarbonate compounds.

2. 2. The method for producing expanded poly(3-hydroxyalkanoate) resin beads according to claim 1, wherein the dispersing step further comprises a heating step of raising the temperature inside the container to 120.0°C to 140.0°C, and a holding step of holding the temperature inside the container at that temperature for 20 minutes or more.

3. The method for producing expanded poly(3-hydroxyalkanoate)-based resin particles according to claim 1 or 2, wherein the poly(3-hydroxyalkanoate)-based resin particles contain two or more poly(3-hydroxyalkanoate)-based resins each having a different weight-average molecular weight.

4. the dispersion step further includes a pressure increasing step of increasing the pressure in the container to 1.0 MPa to 10.0 MPa (gauge pressure), 3. The method for producing expanded poly(3-hydroxyalkanoate) resin beads according to claim 2, wherein the temperature and pressure in the container are maintained for 20 minutes or longer in the maintaining step.

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