Manufacturing method of poly(3-hydroxyalkanoate)-based expanded beads

Abstract

To provide P3HA-based foamed particles having a low content of interconnected voids.SOLUTION: A method for producing second P3HA-based foamed particles includes a compression step for compressing first P3HA-based foamed particles in a container and a dispensing step for dispensing the first P3HA-based foamed particles out of the container while or after releasing the pressure in the container so as to meet specific conditions.SELECTED DRAWING: None

Description

[Technical Field]

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

[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. In recent years, microplastics have become a major problem in the marine environment. For this reason, biodegradable plastics, which can be decomposed by microorganisms in (a) the ocean, soil, and other environments, and (b) landfills and compost, have attracted attention. Development of biodegradable plastics is underway for a wide range of applications, including (a) agricultural, forestry, and fishery materials used in the environment, and (b) food containers, packaging materials, sanitary products, garbage bags, and other items that are difficult to recover and reuse after use. Furthermore, foam molded products made from biodegradable plastics are expected to be used in packaging cushioning, agricultural product boxes, fish boxes, automotive components, building materials, civil engineering materials, and more.

[0003] Among the biodegradable plastics, poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as "P3HA"), a plastic derived from plant materials, has attracted attention from the viewpoints of excellent biodegradability and carbon neutrality.

[0004] The use of the biodegradable plastics described above for moldings has been investigated. For example, Patent Document 1 discloses expanded beads made of poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), a biodegradable aliphatic polyester resin, and a method for producing an in-mold foamed article using the expanded beads. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2000-319438 Summary of the Invention [Problem to be solved by the invention]

[0006] However, the above-mentioned conventional techniques have room for further improvement in terms of the open cell ratio of poly(3-hydroxyalkanoate) expanded beads.

[0007] In view of the above circumstances, an object of one embodiment of the present invention is to provide expanded poly(3-hydroxyalkanoate) beads having a low open cell content. [Means for solving the problem]

[0008] The present inventors have conducted extensive research to solve the above problems and have completed the present invention.

[0009] That is, one embodiment of the present invention includes the following configuration. [1] A method for producing a second poly(3-hydroxyalkanoate)-based expanded particle, comprising: a pressurizing step of supplying first poly(3-hydroxyalkanoate)-based expanded particles into a container and pressurizing the first poly(3-hydroxyalkanoate)-based expanded particles; and a discharging step of discharging the first poly(3-hydroxyalkanoate)-based expanded particles from the container while releasing the pressure in the container or after releasing the pressure in the container, wherein the pressure in the container is released in the discharging step so as to satisfy the following formula (1): pressure release rate (MPa / sec) × pressure in container (gauge pressure) at pressure release (MPa) / area of ​​pressure release port (m 2 )<10.00...Equation (1). [2] The method for producing second poly(3-hydroxyalkanoate)-based expanded beads according to [1], wherein the pressurizing step is a step of pressurizing the first poly(3-hydroxyalkanoate)-based expanded beads so that the pressure (absolute pressure) inside the second poly(3-hydroxyalkanoate)-based expanded beads is 0.12 MPa to 0.35 MPa. [3] The second method for producing expanded poly(3-hydroxyalkanoate) beads according to [1] or [2], wherein the pressure release rate is 0.0001 MPa / sec to 0.0350 MPa / sec. [4] The second method for producing expanded poly(3-hydroxyalkanoate) beads according to any one of [1] to [3], wherein the pressure (gauge pressure) inside the container when the pressure is released is 0.04 MPa to 0.50 MPa. [5] The area of ​​the pressure relief port is 0.0005 m 2 ~0.0100m 2 The second method for producing expanded poly(3-hydroxyalkanoate) beads according to any one of [1] to [4], wherein: [6] The second method for producing expanded poly(3-hydroxyalkanoate) beads according to any one of [1] to [5], wherein in the discharging step, the temperature inside the container is 10°C to 60°C when the pressure is released. [7] A method for producing a second expanded poly(3-hydroxyalkanoate)-based particle according to any one of [1] to [6], wherein the first expanded poly(3-hydroxyalkanoate)-based particle is crosslinked with an organic peroxide. [8] The second method for producing expanded poly(3-hydroxyalkanoate) beads according to [7], wherein the organic peroxide has a t-butoxy group and / or a cumyloxy group. [9] A method for producing a poly(3-hydroxyalkanoate)-based expanded molded article, comprising a step of molding the second poly(3-hydroxyalkanoate)-based expanded beads produced by the method for producing the second poly(3-hydroxyalkanoate)-based expanded beads described in any one of [1] to [8].

[10] Second poly(3-hydroxyalkanoate)-based expanded beads are discharged from a container after first poly(3-hydroxyalkanoate)-based expanded beads are subjected to a pressure treatment in the container, wherein the difference between the open cell rate of the first poly(3-hydroxyalkanoate)-based expanded beads and the open cell rate of the second poly(3-hydroxyalkanoate)-based expanded beads is 0% to 4%, and the open cell rate of the second poly(3-hydroxyalkanoate)-based expanded beads is 9.5% or less. [Effects of the Invention]

[0010] According to one embodiment of the present invention, it is possible to provide expanded poly(3-hydroxyalkanoate) beads having a low open cell rate. DETAILED DESCRIPTION OF THE INVENTION

[0011] 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)."

[0012] In this specification, poly(3-hydroxyalkanoate)-based expanded beads may be referred to as "P3HA-based expanded beads" or "expanded beads," and poly(3-hydroxyalkanoate)-based expanded molded products may be referred to as "P3HA-based expanded molded products" or "expanded molded products." In addition, in a method for producing P3HA-based expanded beads according to one embodiment of the present invention, both the material used in the method and the product obtained by the method are P3HA-based expanded beads. However, the internal pressure of the P3HA-based expanded beads obtained by the method according to one embodiment of the present invention is higher than the internal pressure of the P3HA-based expanded beads that are the material used in the method. For convenience, in this specification, (a) the P3HA-based expanded beads, which are the raw material for the method for producing P3HA-based expanded beads according to one embodiment of the present invention, and the P3HA-based expanded beads being processed in the method (i.e., present in a container) may be referred to as "first poly(3-hydroxyalkanoate)-based expanded beads," "first P3HA-based expanded beads," or "first expanded beads." Also, (b) the P3HA-based expanded beads obtained by the method for producing P3HA-based expanded beads according to one embodiment of the present invention (i.e., discharged from a container) may be referred to as "second poly(3-hydroxyalkanoate)-based expanded beads," "second P3HA-based expanded beads," or "second expanded beads." Furthermore, in this specification, when there is no need to distinguish between the first and second expanded beads, they may simply be referred to as "expanded beads." That is, "expanded beads" refers to both the first and second expanded beads.

[0013] In addition, the P3HA-based expanded beads (second P3HA-based expanded beads) obtained by carrying out the method for producing P3HA-based expanded beads according to one embodiment of the present invention may be subjected again to the method for producing P3HA-based expanded beads according to one embodiment of the present invention.

[0014] 1. Technical Concept of One Embodiment of the Present Invention In order to obtain a P3HA foam molded article with a beautiful surface, a high internal fusion rate, and little shrinkage using conventional P3HA foam beads such as those described in Patent Document 1, there was room for further improvement.

[0015] Here, the lower the open cell rate of the P3HA-based expanded beads, the more beautiful the surface, the higher the internal fusion rate, and the less shrinkage the P3HA-based expanded molded article that can be obtained.

[0016] The present inventors have independently discovered that even P3HA-based expanded beads with a low open cell ratio immediately after production may produce P3HA-based expanded molded articles with poor surface appearance, poor internal fusion rate, and poor shrinkage. The present inventors have conducted extensive research to determine the reason for this.

[0017] During intensive research, the present inventors focused on "applying internal pressure" to P3HA-based expanded beads. This "applying internal pressure" step may be performed (a) on first-stage expanded beads when second-stage expanded beads are produced from first-stage expanded beads of P3HA-based expanded beads, or (b) on P3HA-based expanded beads when a P3HA-based expanded molded article is produced from the P3HA-based expanded beads. Using P3HA-based expanded beads after the internal pressure application step for molding has the advantage that the density of the resulting P3HA-based expandable article is not significantly reduced from the density of the P3HA-based expanded beads used as the raw material (the density can be maintained).

[0018] More specifically, in applying internal pressure to the P3HA-based expanded beads, pressure is applied to the P3HA-based expanded beads placed in a container, and the P3HA-based expanded beads are then removed from the container and used for second-stage expansion and / or molding.

[0019] As a result of extensive investigation, the present inventors have independently and surprisingly found that the open cell ratio of the P3HA-based expanded beads obtained after application of internal pressure is increased compared to the P3HA-based expanded beads before application of internal pressure.

[0020] That is, the present inventors independently discovered that even if the open cell rate of the P3HA-based expanded beads is low before the application of internal pressure, the open cell rate of the P3HA-based expanded beads increases after the application of internal pressure, and this may result in deterioration of the surface appearance, internal fusion rate, and shrinkage properties of the resulting foamed molded article.

[0021] Based on these new findings, the inventors conducted further studies with the aim of reducing the difference (increase) in open cell ratio between P3HA-based expanded beads before and after application of internal pressure.

[0022] As a result of extensive research, the inventors independently discovered the following, which led to the completion of the present invention: by removing P3HA-based expanded beads from a container after the application of internal pressure under specific conditions, the difference in open cell ratio between the P3HA-based expanded beads before the application of internal pressure and the P3HA-based expanded beads after the application of internal pressure can be reduced, and as a result, poly(3-hydroxyalkanoate)-based expanded beads with a low open cell ratio can be provided.

[0023] 2. Second Method for Producing Expanded Poly(3-hydroxyalkanoate) Beads A second method for producing expanded poly(3-hydroxyalkanoate)-based beads according to one embodiment of the present invention includes a pressurizing step of supplying first expanded poly(3-hydroxyalkanoate)-based beads into a container and pressurizing the first expanded poly(3-hydroxyalkanoate)-based beads, and a discharging step of discharging the first expanded poly(3-hydroxyalkanoate)-based beads from the container while releasing the pressure in the container or after releasing the pressure in the container, wherein the pressure in the container is released in the discharging step so as to satisfy the following formula (1): pressure release rate (MPa / sec) × pressure in container (gauge pressure) at pressure release (MPa) / area of ​​pressure release port (m 2 )<10.00...Equation (1).

[0024] The present production method has the above-mentioned features, and thus has the advantage of being able to provide second poly(3-hydroxyalkanoate)-based expanded beads with a low open cell rate. Furthermore, the production method also has the advantage of being able to provide second poly(3-hydroxyalkanoate)-based expanded beads that can provide P3HA-based expanded molded articles with a beautiful surface, a high internal fusion rate, and little shrinkage.

[0025] Furthermore, this production method enables poly(3-hydroxyalkanoate) foam molded articles to be used more suitably in applications such as food containers, packaging materials, sanitary products, garbage bags, cushioning materials for packaging, agricultural product boxes, fish boxes, automotive components, building materials, and civil engineering materials, thereby contributing to the achievement of the Sustainable Development Goals (SDGs).

[0026] In this specification, a repeating unit derived from an X monomer may be referred to as an “X unit.” A repeating unit may also be referred to as a structural unit.

[0027] Each component in this production method will be described below.

[0028] (2-1. First Poly(3-hydroxyalkanoate)-Based Expanded Particles) The first poly(3-hydroxyalkanoate)-based expanded particles are expanded particles obtained by introducing a crosslinked structure into poly(3-hydroxyalkanoate)-based resin particles and expanding the poly(3-hydroxyalkanoate)-based resin particles. The poly(3-hydroxyalkanoate)-based resin particles are made of a poly(3-hydroxyalkanoate)-based resin composition containing P3HA. In this specification, the "poly(3-hydroxyalkanoate) (P3HA)-based resin composition" may be referred to as the "resin composition," and the "poly(3-hydroxyalkanoate) (P3HA)-based resin particles" may be referred to as the "resin particles."

[0029] (Poly(3-hydroxyalkanoate)) P3HA 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, P3HA is preferably a polymer containing a repeating unit represented by the following general formula (2): [-CHR-CH2-CO-O-]···(2). In the general formula (2), R is C n H 2n+1where n is 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.

[0030] As P3HA, P3HA produced by a microorganism is particularly preferred. P3HA produced by a microorganism is poly[(R)-3HA] in which all three HA units are (R)-3HA.

[0031] P3HA preferably contains 3HA units (particularly repeating units of general formula (2)) in an amount of 50 mol % or more, more preferably 70 mol % or more, and even more preferably 80 mol % or more of the total repeating units of P3HA (100 mol %). 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.).

[0032] Specific examples of the 3HA unit include a 3-hydroxybutyrate unit, a 3-hydroxyvalerate unit, and a 3-hydroxyhexanoate unit. 3-Hydroxybutyrate has a melting point and tensile strength close to those of propylene. Therefore, it is preferable that the P3HA according to one embodiment of the present invention contains a 3-hydroxybutyrate unit. In this specification, "3-hydroxybutyrate" may also be referred to as "3HB."

[0033] P3HA preferably contains 3HB units (monomer units) in an amount of 80 mol % or more, more preferably 85 mol % or more, based on 100 mol % of all repeating units of P3HA. Particularly preferred P3HA is a polymer containing 3HB units, all of which are (R)-3HB (a polymer produced by a microorganism).

[0034] When P3HA contains two or more 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" may also be referred to as a "comonomer unit."

[0035] The comonomer is not particularly limited, but is preferably 3-hydroxyhexanoate (hereinafter sometimes referred to as 3HH) or 4-hydroxybutyrate (hereinafter sometimes referred to as 4HB).

[0036] Specific examples of P3HA include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter, may be referred to as "P3HB3HV"), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter, may be referred to as "P3HB3HH"), poly Examples of such 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) are preferred. In one embodiment of the present invention, the above-mentioned P3HA may be used alone or in combination of two or more.

[0037] It is preferable that P3HA has 3HB units as an essential repeating unit (structural unit) and also has comonomer units. That is, P3HA is preferably a copolymer having 3HB units and comonomer units. The case where P3HA has 3HB units and comonomer units will be described. In this case, the ratio of 3HB units to comonomer units (3HB units / comonomer units) in 100 mol% of all repeating units in P3HA is preferably 99 / 1 (mol% / mol%) to 80 / 20 (mol% / mol%), more preferably 97 / 3 (mol% / mol%) to 80 / 20 (mol% / mol%), and even more preferably 95 / 5 (mol% / mol%) to 85 / 15 (mol% / mol%). When the ratio of comonomer units in 100 mol% of all repeating units of P3HA is 1 mol% or more, the melt-kneadable temperature range and the thermal decomposition temperature range of P3HA are sufficiently separated, which has the advantage that the resulting expanded beads have excellent processability. On the other hand, if the ratio of comonomer units to 100 mol% of all repeating units of P3HA is 20 mol% or less, crystallization of the P3HA composition during melt-kneading is rapid, and productivity is high. P3HA having such a ratio of each monomer unit can be produced according to a method known to those skilled in the art, for example, the method described in International Publication WO2009 / 145164.

[0038] The ratio of each monomer unit in P3HA can be determined by a method known to those skilled in the art, for example, the method described in WO 2013 / 147139.

[0039] In one embodiment of the present invention, the method for producing P3HA is not particularly limited, and may be a production method by chemical synthesis or a production method using a microorganism. Of these, a production method using a microorganism is preferred. Known methods can be applied to the production of P3HA using a microorganism.

[0040] Specific examples of bacteria that produce copolymers of 3HB with other hydroxyalkanoates include Aeromonas caviae, which produces P3HB3HV and P3HB3HH, and Alcaligenes eutrophus, which produces P3HB4HB. In particular, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, pp. 4821-4830 (1997)), which has been improved in P3HB3HH productivity by introducing genes encoding P3HA synthases, is preferred. Microbial cells, such as Alcaligenes eutrophus AC32, that have been cultured under appropriate conditions to accumulate P3HB3HH within the cells, are suitable for use in P3HA production methods. 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 (fungi), including the type of substrate, may be optimized depending on the P3HA to be produced.

[0041] In one embodiment of the present invention, the method for culturing a microorganism that produces P3HA is not particularly limited, and for example, the method described in International Publication No. WO2019 / 142717 can be used.

[0042] The content of P3HA in the first expanded beads is not particularly limited, but is preferably 70% by weight or more, and more preferably 80% by weight or more, relative to 100% by weight of the expanded beads, since the resulting expanded beads and foamed molded articles have excellent biodegradability.

[0043] The first expanded beads may further contain resin components other than P3HA (sometimes 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. One of these other resin components may be used alone, or two or more may be used in combination with P3HA.

[0044] The content of the other resin components in the first expanded beads is not particularly limited, but is preferably 10 to 400 parts by weight, more preferably 50 to 150 parts by weight, per 100 parts by weight of P3HA.

[0045] (additives) The resin composition may further contain additives in addition to the resin component containing P3HA. Examples of additives that can be used depending on the purpose include crystal nucleating agents, polyalkylene glycols, cell control agents, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, UV absorbers, colorants, inorganic fillers, organic fillers, and hydrolysis inhibitors. Biodegradable additives are particularly preferred. The term "crystal nucleating agent" may also be referred to as "crystallization nucleating agent."

[0046] As the nucleating agent, for example, a conventionally known nucleating agent such as pentaerythritol can be used. The amount of the nucleating agent used is not particularly limited.

[0047] As the cell-forming agent, for example, a conventionally known cell-forming agent such as talc can be used. The amount of the cell-forming agent used is not particularly limited.

[0048] As the lubricant, for example, a conventionally known lubricant such as behenamide, erucamide, etc. The amount of the lubricant used is not particularly limited.

[0049] In addition, it is preferable to use a crosslinking agent in the first expanded bead manufacturing method. By using a crosslinking agent, the P3HA in the resulting first expanded bead becomes P3HA with a crosslinked structure. As a result, it is difficult for cells to open, which has the advantage of producing expanded beads with a low open cell ratio. Because the crosslinking reaction of the P3HA in the resin beads also progresses during the expansion process, the expansion process can also be considered a crosslinking process.

[0050] The crosslinking agent is not particularly limited as long as it can crosslink P3HA. The crosslinking agent is preferably an organic peroxide. In other words, the first expanded poly(3-hydroxyalkanoate) beads are preferably crosslinked with an organic peroxide.

[0051] The organic peroxide will be described in detail later in the section (2-2. First method for producing expanded poly(3-hydroxyalkanoate) beads).

[0052] (Physical Properties of the First Poly(3-hydroxyalkanoate)-Based Expanded Beads) The physical properties of the first poly(3-hydroxyalkanoate)-based expanded beads will be described in detail below.

[0053] (gel fraction) The expanded beads preferably have a crosslinked structure. In this specification, the crosslinked structure of the expanded beads is evaluated by the gel fraction of the expanded beads. The term "expanded beads having 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. The method for crosslinking the expanded beads is not particularly limited, but an example is a method in which a crosslinking agent is added during the production of the expanded beads, as described below. The gel fraction does not change through the pressurizing step and the discharging step. In other words, the gel fraction of the first expanded beads can also be said to be the gel fraction of the second expanded beads, and the gel fraction obtained by analyzing the second expanded beads can also be considered to be the gel fraction of the first expanded beads.

[0054] The gel fraction of the expanded beads is preferably 30% to 80% by weight, more preferably 50% to 80% by weight, and even more preferably 60% to 75% by weight, based on 100% by weight of the expanded beads. When the gel fraction of the expanded beads is (a) 30% by weight or more, based on 100% by weight of the expanded beads, there is an advantage that the molding temperature range of the expanded beads that can provide high-quality expanded molded articles is widened when molding an expanded molded article, thereby improving productivity, and when the gel fraction is (b) 80% by weight or less, there is an advantage that expanded molded articles with excellent surface beauty can be obtained.

[0055] In one embodiment of the present invention, the gel fraction of the expanded beads is an index showing the degree of crosslinking of P3HA in the expanded beads, and can be controlled by the type and / or amount of the crosslinking agent used.

[0056] In this specification, the method for measuring the gel fraction of expanded beads is as follows (1) to (5): (1) 1 g of expanded beads and 100 ml of chloroform are placed in a 150 ml flask; (2) the mixture in the flask is heated under reflux at 62°C under atmospheric pressure for 8 hours; (3) the obtained heat-treated product is filtered using a suction filtration device equipped with a 100-mesh wire mesh; (4) the filtered product on the wire mesh is dried in an oven at 80°C under vacuum conditions for 8 hours, and the weight Wg (g) of the dried product is measured; (5) the gel fraction is calculated using the following formula: Gel fraction (wt%) = Wg / 1 × 100.

[0057] (2-2. First Method for Producing Expanded Poly(3-hydroxyalkanoate)-Based Beads) The first method for producing expanded beads will be described below by taking as an example a production method including, in order, a resin particle preparation step of preparing resin particles and an expansion step of expanding the resin particles. The first method for producing expanded beads is not limited to the following production method.

[0058] (Resin particle preparation process) The resin particle preparation step is a step of preparing P3HA-based resin particles containing P3HA and, if necessary, additives. The resin particle preparation step can be carried out before the foaming step described below. The resin particle preparation step can also be said to be a step of molding a resin composition containing P3HA into a shape that is easy to use for foaming. The mode of the resin particle preparation step is not particularly limited as long as resin particles can be obtained.

[0059] The resin particle preparation step includes: (a) a melt-kneading step of melt-kneading a resin composition containing P3HA and, if necessary, additives; (b) a particle forming step of forming the melt-kneaded resin composition into a shape that is easy to use for foaming. Specific embodiments of the melt-kneading step and the particle forming step are not particularly limited, and conventionally known methods can be used as appropriate.

[0060] (Foaming process) The form of the expansion step in the first method for producing expanded beads is not particularly limited as long as it can expand the resin beads. (a) a dispersing step of dispersing resin particles, an aqueous dispersion medium, a crosslinking agent, a foaming agent, and optionally 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 increasing the pressure inside the container to a constant pressure; (c) maintaining the temperature and pressure in the container at a constant temperature and constant pressure; (d) a discharging step of opening one end of the container and discharging the dispersion liquid in the container into a region (space) having a pressure lower than the foaming pressure (i.e., the pressure inside the container).

[0061] The specific embodiments of the dispersing step, the temperature-pressure increasing step, the holding step, and the releasing step in the foaming step are not particularly limited, and conventionally known methods can be used as appropriate.

[0062] In the first method for producing expanded beads, as described above, it is preferable to use a crosslinking agent. By using a crosslinking agent, the P3HA in the resulting first expanded beads becomes P3HA with a crosslinked structure. Because the crosslinking reaction of the P3HA in the resin beads also progresses during the expansion process, the expansion process can also be considered a crosslinking process.

[0063] 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 expanded poly(3-hydroxyalkanoate)-based particles are preferably crosslinked with an organic peroxide. The organic peroxide may be used in (a) the resin particle production process, (b) the expansion process (e.g., the dispersion process), or (c) the resin particle production process and the expansion process (e.g., the dispersion process). More specifically, to react the organic peroxide with P3HA, (a) the organic peroxide and P3HA may be melt-kneaded in the resin particle production process, (b) the resin particles and the organic peroxide may be dispersed in an aqueous dispersion medium in the dispersion process of the expansion process, or (c) the organic peroxide and P3HA may be melt-kneaded and further dispersed in an aqueous dispersion medium. In the dispersion step of the expansion process, the resin particles produced in the resin particle production step and an organic peroxide are dispersed in an aqueous dispersion medium, allowing the organic peroxide to be impregnated into the resin particles and react with them. For these reasons, an organic peroxide is preferred as a crosslinking agent in the expanded particle production method. When an organic peroxide is used as a crosslinking agent, the molecular chains of P3HA are directly bonded to each other (without going through a structure derived from the crosslinking agent), thereby forming a crosslinked structure.

[0064] 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. Specific examples include 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), and t-amylperoxyisopropyl carbonate (TAIC, one-hour half-life temperature: 118°C). : 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), °C), di-t-butyl peroxide (one-hour half-life temperature: 149 °C), 1,1-di(t-butylperoxy)cyclohexane (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), 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane (one-hour half-life temperature: 114 °C), and the like.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.

[0065] As the organic peroxide 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-di(t-butylperoxy)cyclohexane, 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.

[0066] 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 expanded molded articles with a high internal fusion rate can be easily obtained by applying a lower internal pressure than in the prior art.

[0067] 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 part 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 a good surface appearance 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 added can be obtained, eliminating the 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 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 foaming step (e.g., the dispersion step) may already contain a crosslinking agent. In such cases, it is preferable that the total amount of the crosslinking agent already contained in the resin particles before the foaming step and the amount of the crosslinking agent used in the foaming step (e.g., the dispersion step) falls within the above range.

[0068] 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 standpoint 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 adjusted appropriately depending on the purpose.

[0069] 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 added is obtained, so economic waste does not occur.

[0070] In the first method for producing expanded beads, it is preferable to use a dispersant. The use of a dispersant has the advantage of suppressing adhesion of resin particles (sometimes referred to as blocking) and 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. One of these dispersants may be used alone, or two or more may be used in combination. When two or more dispersants are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0071] The amount of the 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, relative to 100 parts by weight of the resin particles.

[0072] In the dispersion step of the foaming process, when the resin particles are impregnated with and reacted with a crosslinking agent, it is preferable to reduce the oxygen concentration in the container and the amount of dissolved oxygen in the dispersion to increase the crosslinking efficiency of P3HA. Methods for reducing 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.

[0073] 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.

[0074] The amount of the dispersing agent used is not particularly limited, but is preferably 0.001 to 0.500 parts by weight, and more preferably 0.010 to 0.200 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 agent in combination.

[0075] (2-3. Second Method for Producing Expanded Poly(3-hydroxyalkanoate)-Based Beads) By applying internal pressure to the first poly(3-hydroxyalkanoate) expanded beads described above, second poly(3-hydroxyalkanoate) expanded beads can be obtained.

[0076] Specific steps included in this manufacturing method will be described below.

[0077] (Pressure process) The pressurizing step is a step of adjusting the pressure inside the first expanded beads by pressurizing the first expanded beads in the container after putting the first expanded beads into the container. Note that the "pressure inside the expanded beads" can also be called the "internal pressure of the expanded beads." The pressurizing step can also be called a step of applying internal pressure to the first expanded beads.

[0078] The container used in this production method is not particularly limited, but is preferably a container that can withstand pressure treatment, for example, a pressure-resistant container.

[0079] In the pressurizing step, the method for pressurizing the inside of the container is not particularly limited, but examples include a method of introducing (pressurizing) an inorganic gas into the container. In the pressurizing step, by introducing an inorganic gas into the container, the inside of the container can be pressurized and the first expanded beads in the container can be impregnated with the inorganic gas. As a result, internal pressure can be applied to the first expanded beads in the container. In the pressurizing step, by adjusting the amount of inorganic gas introduced into the container, the pressure in the container can be adjusted to a desired set pressure, and the internal pressure of the first expanded beads in the container (in other words, the internal pressure of the resulting second expanded beads) can be adjusted to a desired internal pressure.

[0080] Specific examples of inorganic gases used in the pressurization step include air, nitrogen, oxygen, carbon dioxide, helium, neon, and argon. One of these inorganic gases may be used alone, or two or more may be used in combination. When two or more inorganic gases are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose. Among these inorganic gases, air and / or carbon dioxide are preferred, and air is more preferred, as they improve the productivity of foamed molded articles and reduce costs.

[0081] In this specification, the pressure inside the container set to impart internal pressure to the first expanded beads in the pressurizing step is referred to as the “set pressure.” In other words, in the pressurizing step, the pressure inside the container is increased (pressurized) to the set pressure and maintained at the set pressure for a certain period of time, thereby imparting internal pressure to the first expanded beads.

[0082] The pressure set in the pressurizing step may be appropriately set depending on the desired internal pressure to be imparted to the first expanded beads. The set pressure is, for example, preferably 0.10 MPa (gauge pressure) to 0.50 MPa (gauge pressure), more preferably 0.10 MPa (gauge pressure) to 0.40 MPa (gauge pressure), further preferably 0.10 MPa (gauge pressure) to 0.30 MPa (gauge pressure), and particularly preferably 0.10 MPa (gauge pressure) to 0.25 MPa (gauge pressure). This configuration has the advantage of being able to impart a desired internal pressure to the first poly(3-hydroxyalkanoate)-based expanded beads.

[0083] The pressurization step is preferably a step of pressurizing the first P3HA-based expanded beads so that the internal pressure (absolute pressure) of the second P3HA-based expanded beads is 0.12 MPa (absolute pressure) to 0.35 MPa (absolute pressure). In other words, the internal pressure (absolute pressure) of the second P3HA-based expanded beads obtained by this production method is preferably 0.12 MPa (absolute pressure) to 0.35 MPa (absolute pressure). The internal pressure (absolute pressure) of the second P3HA-based expanded beads obtained by this production method is more preferably 0.13 MPa (absolute pressure) to 0.34 MPa (absolute pressure), more preferably 0.14 MPa (absolute pressure) to 0.30 MPa (absolute pressure), even more preferably 0.15 MPa (absolute pressure) to 0.25 MPa (absolute pressure), and particularly preferably 0.16 MPa (absolute pressure) to 0.19 MPa (absolute pressure). When the pressure (absolute pressure) inside the second P3HA-based expanded beads is 0.120 MPa (absolute pressure) or higher, the expanded beads expand sufficiently inside the mold during in-mold foam molding using a mold, resulting in a foamed molded article with excellent surface beauty and shrinkage. Furthermore, when the pressurization step is a step of pressurizing the first P3HA-based expanded beads so that the pressure (absolute pressure) inside the second P3HA-based expanded beads is 0.12 MPa (absolute pressure) to 0.19 MPa (absolute pressure), the following advantages are particularly apparent: (a) foamed molded articles with even more excellent surface beauty and shrinkage can be produced; and (b) during in-mold foam molding, there is no risk of rapid expansion of only the expanded beads relatively close to the mold, allowing steam to reach the expanded beads inside the mold. As a result, foamed molded articles with excellent fusion properties can be produced. Furthermore, when the pressurization step is a step of pressurizing the first P3HA-based expanded beads so that the pressure (absolute pressure) inside the second P3HA-based expanded beads is more than 0.19 MPa (absolute pressure) and not more than 0.35 MPa (absolute pressure), the following particular advantage is obtained: the shape of the second expanded beads can be maintained even when a long time passes between the production of the second expanded beads and the in-mold foam molding (for example, when the second expanded beads are produced and then shipped to a separate factory for use in in-mold foam molding). Therefore, there is an advantage in that a foam molded article with excellent surface beauty, internal fusion rate, and shrinkage can be provided.

[0084] In this specification, the method for measuring the pressure inside the second expanded beads (internal pressure of the second expanded beads) is as follows (1) to (5): (1) measuring the weight W1 (g) of the second expanded beads; (2) heating the second expanded beads at 150°C for 30 minutes to dissipate the inorganic gas inside the second expanded beads; (3) measuring the weight W2 (g) of the second expanded beads from which the inorganic gas has dissipated; (4) calculating the weight of the inorganic gas (ΔW) from the difference (W1 - W2) between the weights of the second expanded beads before and after dissipation of the inorganic gas; (5) calculating the pressure P (MPa (absolute pressure)) inside the second expanded beads using the equation of state of an ideal gas (for example, the following formula): Pressure inside the foam particles P (MPa (absolute pressure)) = (1 + ΔW / 28.8 × 0.082 × (273 + T) × (ρ × 1000 / W2)) / 9.87 In the above formula, T is the temperature (room temperature) when the weight of the second expanded beads is measured, and ρ is the apparent density (g / cc) of the second expanded beads (expanded beads having a weight W1).

[0085] In this specification, the method for measuring the apparent density of the pressure inside the second expanded beads (internal pressure of the second expanded beads) is as follows (1) to (3): (1) prepare a measuring cylinder containing ethanol, and submerge the second expanded beads with a weight Wd (g) in the ethanol; (2) determine the volume of the second expanded beads as Vd (cc) based on the rise in the water level of the ethanol (submersion method); (3) calculate the apparent density of the second expanded beads using the following formula: Apparent density (g / cc) = Wd / Vd.

[0086] Here, the internal pressure of the second expanded beads decreases over time. However, compared to expanded beads obtained from polyethylene, polypropylene, etc., the internal pressure of P3HA-based expanded beads is less likely to decrease, and has the advantage of being able to maintain its internal pressure for a long period of time. As described above, the internal pressure (absolute pressure) of the P3HA-based expanded beads during the production of a molded article is preferably 0.12 MPa (absolute pressure) to 0.19 MPa (absolute pressure). Therefore, the pressurizing step in this production method is preferably a step of pressurizing the first P3HA-based expanded beads so that the internal pressure (absolute pressure) of the second P3HA-based expanded beads is 0.12 MPa (absolute pressure) to 0.35 MPa (absolute pressure). Furthermore, in consideration of the decrease in the internal pressure of the second P3HA-based expanded beads over time, it is preferable to adjust the internal pressure applied to the first expanded beads during the pressurizing step so that the internal pressure of the second expanded beads becomes an internal pressure suitable for molding (0.12 MPa (absolute pressure) to 0.19 MPa (absolute pressure)) during the production of a molded article.

[0087] In the pressurizing step, the pressure inside the container may be maintained at a pressure higher than the set pressure for a certain period of time before the pressure inside the container is maintained at the set pressure. This configuration has the advantage of shortening the time required to apply internal pressure to the first expanded beads, in other words, the time required for the pressurizing step. When the pressure inside the container is maintained at a pressure higher than the set pressure for a certain period of time before the pressure inside the container is maintained at the set pressure, the time for which the pressure inside the container is maintained at a pressure higher than the set pressure is usually shorter than the time for which the pressure inside the container is maintained at the set pressure. Furthermore, in the pressurizing step, the pressure inside the container may be maintained at a pressure higher or lower than the set pressure for a certain period of time after the pressure inside the container is maintained at the set pressure. When the pressure inside the container is maintained at a pressure higher or lower than the set pressure for a certain period of time after the pressure inside the container is maintained at the set pressure, the time for which the pressure inside the container is maintained at a pressure higher or lower than the set pressure is usually shorter than the time for which the pressure inside the container is maintained at the set pressure. Therefore, the set pressure can also be said to be the pressure inside the container that is maintained for the longest period of time in the pressurizing step.

[0088] The temperature inside the container in the pressurizing step is not particularly limited. The pressurizing container and the first expanded beads may be heated before the first expanded beads are placed in the container. The temperature inside the container in the pressurizing step is preferably 10°C to 90°C, more preferably 40°C to 90°C, for example, since this allows for efficient application of internal pressure. The temperature inside the container may be adjusted to within the above-mentioned range before the first expanded beads are placed in the container, or may be adjusted to within the above-mentioned range after the first expanded beads are placed in the container. The pressure inside the container may be increased to a set temperature and the temperature inside the container may be adjusted to within the above-mentioned range in the pressurizing step. The pressure inside the container may be increased to a set temperature and the temperature inside the container may be adjusted to within the above-mentioned range after the pressure inside the container is increased to a set temperature.

[0089] (Discharge process) The discharging step is a step of discharging or taking out the first expanded beads to which internal pressure has been applied from the container while or after releasing the pressure inside the container. "Releasing the pressure inside the container" can also be said to be "reducing the pressure inside the container that was increased in the pressurizing step." The discharging step can also be said to be a step of obtaining the second expanded beads to which internal pressure has been applied.

[0090] In the discharging step, the method for releasing the pressure inside the container is not particularly limited, but for example, a method of discharging the inorganic gas (gas) introduced into the container to the outside of the container can be mentioned.

[0091] The container used in this manufacturing method may be provided with (a) a pressure release section for releasing the pressure inside the container, and (b) an expanded bead removal section for removing the first expanded beads inside the container. The pressure release section may be provided with an opening and a valve for controlling the opening and closing of the pressure release section. The pressure release section and the expanded bead removal section may be the same member. Suitable examples of the container include (a) a pressure-resistant container provided with a discharge section, or (b) a pressure-resistant container provided with a purge line and a manhole or side hole.

[0092] In this manufacturing method, a case where a container equipped with a dispensing unit is used as the container (Case A) will be described. The dispensing unit includes, for example, a valve for controlling the opening and closing of the dispensing unit and a dispensing port. In Case A, the pressure inside the container is released by opening the valve of the dispensing unit, and the first expanded beads inside the container can be dispensed to the outside of the container through the dispensing port of the dispensing unit by utilizing the pressure difference between the inside and outside of the container. Therefore, in Case A, the dispensing unit is both a pressure release unit and an expanded bead removal unit. Also, in Case A, the pressure release port is the dispensing port of the dispensing unit. In other words, the area of ​​the pressure release port is the cross-sectional area of ​​the dispensing port.

[0093] The following describes a case where a container equipped with a purge line and a manhole or side hole is used as the container (Case B). In Case B, the purge line is a pressure release section, and is equipped with, for example, a valve for controlling the opening and closing of the purge line and an opening. In Case B, the manhole or side hole is an expanded particle removal section. In Case B, the pressure inside the container is released (to atmospheric pressure, for example) by opening the valve of the purge line, and then the first expanded particles inside the container can be removed (discharged) from the container through the manhole or side hole. In Case B, the pressure release port is the opening of the purge line. In other words, the area of ​​the pressure release port is the cross-sectional area of ​​the opening of the purge line.

[0094] In the dispensing step, the pressure inside the container when the pressure inside the container is released is referred to as the “pressure inside the container at the time of pressure release (gauge pressure).” The pressure inside the container at the time of pressure release can also be said to be the pressure inside the container immediately before the valve of the pressure release part provided in the container is opened.

[0095] In the discharging process, the pressure drop from opening to closing the valve of the pressure release section is defined as the "pressure drop," and the time elapsed from opening to closing the valve of the pressure release section is defined as the "discharging time." However, in the above-mentioned case A, if all the expanded beads in the container are discharged while the valve of the discharging section (pressure release section) is open, (a) the pressure inside the container that drops from opening the valve of the discharging section until all the expanded beads are discharged from the container is defined as the "pressure drop," and (b) the time elapsed from opening the valve of the discharging section until all the expanded beads are discharged from the container is defined as the "discharging time." Furthermore, in the above-mentioned case B, if the pressure inside the container is released to atmospheric pressure, (a) the difference between the pressure inside the container and atmospheric pressure is defined as the "pressure drop," and (b) the time elapsed from opening the valve of the purge line until the pressure inside the container becomes atmospheric pressure is defined as the "discharging time."

[0096] The pressure (gauge pressure) inside the container when the pressure is released is preferably 0.04 MPa (gauge pressure) to 0.50 MPa (gauge pressure), more preferably 0.06 MPa (gauge pressure) to 0.30 MPa (gauge pressure), and even more preferably 0.08 MPa (gauge pressure) to 0.20 MPa (gauge pressure). When the pressure (gauge pressure) inside the container when the pressure is released is 0.04 MPa or more, it is advantageous that internal pressure can be efficiently applied to the first expanded beads. When the pressure (gauge pressure) inside the container when the pressure is released is 0.50 MPa or less, it is advantageous that a heavy-duty container capable of withstanding high pressure does not need to be used, and a general pressure-resistant container can be used. The pressure (gauge pressure) inside the container when the pressure is released may be, for example, the set pressure in the pressurizing step. In other words, after the pressure inside the container is maintained at the set pressure in the pressurizing step, pressure release may be performed without changing the pressure inside the container.

[0097] In this specification, the value obtained by dividing the pressure drop (MPa) by the dispensing time (seconds) is referred to as the "pressure release rate." The pressure release rate is preferably 0.0001 MPa / second to 0.0350 MPa / second, more preferably 0.0001 MPa / second to 0.0345 MPa / second, even more preferably 0.0001 MPa / second to 0.0335 MPa / second, and particularly preferably 0.0001 MPa / second to 0.0050 MPa / second. The pressure release rate can be faster than 0.0000 MPa / second and can actually be 0.0001 MPa / second or higher. A dispensing rate of 0.00350 MPa / second or lower has the advantage of reducing the difference (increase) in the open cell ratio of the expanded molded particles before and after carrying out this production method.

[0098] The area of ​​the pressure relief port is 0.0005m 2 ~0.0100m 2 It is preferable that the thickness is 0.0005 m. 2 ~0.0050m 2 is more preferable, and 0.0005m 2 ~0.0030m 2 is more preferable, and 0.0005 m 2 ~0.0025m 2 is particularly preferable. This configuration has the advantage that the second expanded beads can be easily expelled from the container. When the cross section of the pressure release port is circular, the area of ​​the pressure release port can be calculated from the diameter of the cross section of the pressure release port.

[0099] In addition, in the second method for producing expanded poly(3-hydroxyalkanoate) beads according to one embodiment of the present invention, the discharging step satisfies the following formula (1): Pressure release speed (MPa / sec) x pressure inside the container when pressure is released (gauge pressure) (MPa) / area of ​​pressure release port (m 2 )<10.00...Equation (1).

[0100] Pressure release speed (MPa / sec) x pressure inside the container when pressure is released (gauge pressure) (MPa) / area of ​​pressure release port (m 2) is less than 10.00, preferably less than 9.00, more preferably less than 8.00, even more preferably less than 7.00, and particularly preferably less than 6.00.

[0101] The present inventors have independently and surprisingly found that the value of the formula (1) correlates with the difference between the open cell ratio of the first poly(3-hydroxyalkanoate)-based expanded beads and the open cell ratio of the second poly(3-hydroxyalkanoate)-based expanded beads, as described below. In other words, the smaller the value of the formula (1), the smaller the difference in the open cell ratios, which is more preferable.

[0102] In the discharging step, the inside of the container may be cooled. By cooling the inside of the container, the first expanded beads in the container can be cooled. In this specification, the temperature inside the container when the pressure inside the container is released in the discharging step (in other words, immediately before the valve of the pressure release section is opened) is referred to as the "temperature inside the container at the time of pressure release." In other words, after adjusting the temperature inside the container in the pressurizing step, the inside of the container may be cooled to the temperature inside the container at the time of pressure release in the pressurizing step and / or the discharging step. The temperature inside the container at the time of pressure release is preferably 10°C to 60°C, more preferably 15°C to 55°C, even more preferably 20°C to 50°C, and particularly preferably 25°C to 45°C. Here, 15°C to 25°C can also be considered room temperature. Therefore, in other words, the temperature inside the container at the time of pressure release is preferably room temperature to 60°C, more preferably room temperature to 55°C, even more preferably room temperature to 50°C, and particularly preferably room temperature to 45°C. When the temperature inside the container when the pressure is released is within the above range, there is an advantage that the open cell ratio of the obtained second expanded beads is low.

[0103] 3. Second Poly(3-hydroxyalkanoate)-Based Expanded Particles The second P3HA-based expanded beads according to one embodiment of the present invention are second poly(3-hydroxyalkanoate)-based expanded beads discharged from a container after pressure treatment of the first poly(3-hydroxyalkanoate)-based expanded beads in the container, wherein the difference between the open cell ratio of the first poly(3-hydroxyalkanoate)-based expanded beads and the open cell ratio of the second poly(3-hydroxyalkanoate)-based expanded beads is 0% to 4%, and the open cell ratio of the second poly(3-hydroxyalkanoate)-based expanded beads is 9.5% or less.

[0104] The second P3HA-based expanded beads according to one embodiment of the present invention have the above-described configuration, and therefore have the advantage of being able to provide P3HA-based expanded molded articles with beautiful surfaces, a high internal fusion rate, and little shrinkage.

[0105] The difference between the open cell fraction of the first P3HA-based expanded beads and the open cell fraction of the second P3HA-based expanded beads is 0.0% to 4.0%, preferably 0.0% to 3.5%, more preferably 0.0% to 3.0%, even more preferably 0.0% to 2.5%, and particularly preferably 0.0% to 1.5%. This configuration provides a method for producing second P3HA-based expanded beads having a low open cell fraction. When the difference between the open cell fraction and the open cell fraction is within the above-mentioned range, the resulting second P3HA-based expanded beads have the advantages of a more beautiful surface, a higher internal fusion rate, and less shrinkage, resulting in a P3HA-based expanded molded article.

[0106] The second P3HA-based expanded beads have an open cell ratio of 9.5% or less, preferably 9.0% or less, more preferably 8.5% or less, even more preferably 8.0% or less, and particularly preferably 7.5% or less. This configuration provides a method for producing second P3HA-based expanded beads having a low open cell ratio, and therefore has the advantage of being able to provide P3HA-based expanded molded articles with a more beautiful surface, a higher internal fusion ratio, and less shrinkage.

[0107] The second P3HA-based expanded beads according to one embodiment of the present invention are preferably obtained by the production method described in the section "2. Production method for second poly(3-hydroxyalkanoate)-based expanded beads."

[0108] The second P3HA-based expanded beads according to one embodiment of the present invention can be used to produce second-stage expanded beads, and can also be used to produce poly(3-hydroxyalkanoate)-based expanded molded articles.

[0109] (two-stage foaming) In the first expanded bead manufacturing method described above, the expansion step alone may not produce expanded beads with the desired apparent density. In such cases, the first expanded beads obtained by the first expanded bead manufacturing method may be subjected to this manufacturing method to further expand (expand) the resulting second expanded beads. Further expanding the second expanded beads is called "second-stage expansion," and this process is called the "second-stage expansion process." By performing this manufacturing method and the second-stage expansion process on the first expanded beads, expanded beads with an apparent density even lower than that of the first expanded beads obtained by the expansion process described above can be obtained.

[0110] In the second-stage expansion process, for example, the second expanded beads are heated with steam or the like to further expand them, thereby obtaining expanded beads with a desired apparent density. The expanded beads obtained in the second-stage expansion process are sometimes referred to as second-stage expanded beads. When the second-stage expansion process is performed, the expansion process is sometimes referred to as the first-stage expansion process, and the expanded beads obtained in the first-stage expansion process are sometimes referred to as first-stage expanded beads.

[0111] In the second-stage expansion step, the pressure of the steam or the like used to heat the second expanded beads (hereinafter, sometimes referred to as the "second-stage expansion pressure") varies depending on the properties of the expanded beads used and the desired apparent density, and cannot be generally defined. The second-stage expansion pressure is preferably 0.01 MPa (gauge pressure) to 0.17 MPa (gauge pressure), and more preferably 0.03 MPa (gauge pressure) to 0.11 MPa (gauge pressure).

[0112] The gel fraction of the second-stage expanded beads is preferably the same as that of the first expanded beads, i.e., the description in the above section (Gel fraction) can be used as appropriate for the gel fraction of the second-stage expanded beads.

[0113] 4. Method for producing poly(3-hydroxyalkanoate) foamed molded articles A method for producing a poly(3-hydroxyalkanoate)-based expanded molded article according to one embodiment of the present invention includes a step of molding second poly(3-hydroxyalkanoate)-based expanded beads produced by the method described in Section [2. Method for producing second poly(3-hydroxyalkanoate)-based expanded beads] or the second poly(3-hydroxyalkanoate)-based expanded beads described in Section [3. Second poly(3-hydroxyalkanoate)-based expanded beads].

[0114] The method for producing a poly(3-hydroxyalkanoate)-based foam molded article according to one embodiment of the present invention has the above-mentioned configuration, and therefore has the advantage of being able to provide a poly(3-hydroxyalkanoate)-based foam molded article with a beautiful surface, a high internal fusion rate, and little shrinkage.

[0115] The poly(3-hydroxyalkanoate)-based expanded molded article according to one embodiment of the present invention can also be said to be an expanded molded article obtained by molding the second poly(3-hydroxyalkanoate)-based expanded beads obtained by the manufacturing method described in Section [2. Manufacturing method for second poly(3-hydroxyalkanoate)-based expanded beads], or the second poly(3-hydroxyalkanoate)-based expanded beads described in Section [3. Second poly(3-hydroxyalkanoate)-based expanded beads].

[0116] In one embodiment of the present invention, the following steps (1) to (4) may be carried out in this order: (1) subjecting the first expanded beads obtained by the first expanded bead production method to the present production method to obtain second expanded beads; (2) The second expanded beads obtained in (1) are subjected to the second-stage expansion step described above to obtain second expanded beads (second-stage expanded beads) having an apparent density lower than that of the first expanded beads; (3) subjecting the second-stage expanded beads obtained in (2) above to the present production method to obtain second expanded beads (second-stage expanded beads to which internal pressure has been applied); (4) The second-stage expanded beads to which internal pressure has been applied obtained in (3) above are subjected to a method for producing a poly(3-hydroxyalkanoate)-based expanded molded article according to one embodiment of the present invention to obtain an expanded molded article. The second-stage expanded beads obtained in (1) are expanded beads to which internal pressure has been applied, whereas the second-stage expanded beads obtained in (2) are expanded beads to which no internal pressure has been applied because they have undergone the second-stage expansion step in (2). In (3), the second-stage expanded beads are subjected to this production method, thereby applying internal pressure again to the second-stage expanded beads to which no internal pressure has been applied. Then, in (4), a foamed molded article is obtained using the second-stage expanded beads to which internal pressure has been applied.

[0117] Hereinafter, specific steps included in the method for producing a P3HA-based foam molded article according to one embodiment of the present invention will be described.

[0118] Using the second expanded beads, various foamed molded articles can be obtained by various molding methods. Hereinafter, a method for producing a P3HA-based foamed molded article according to one embodiment of the present invention will be described in more detail, taking an in-mold foam molding method using a mold as an example. It should be noted that the method for producing a P3HA-based foamed molded article according to one embodiment of the present invention is not limited to the in-mold foam molding method.

[0119] (Mold) The mold is not particularly limited, and an example thereof is a mold equipped with a fixed mold and a movable mold. The movable mold of the mold can be said to be a drivable mold, and the fixed mold of the mold can be said to be a non-drivable mold. The fixed mold and the movable mold can form a molding space inside the fixed mold and the movable mold by driving the movable mold toward the fixed mold (this operation is sometimes referred to as "mold closing").

[0120] The method for producing a P3HA-based foam molded article according to one embodiment of the present invention preferably includes the following steps subsequent to the pressurizing step.

[0121] (i) a filling step of filling the foamed beads to which internal pressure has been applied in the pressurizing step into a molding space of a mold; and (ii) A foam molding step in which the foamed beads filled in the molding space of the mold in the filling step are heated to fuse the foamed beads.

[0122] (filling process) The internal pressure of the expanded beads to which internal pressure has been applied decreases over time. However, as described above, the expanded beads can maintain an internal pressure suitable for molding for a long period of time after the application of internal pressure. Therefore, taking into account the decrease in the internal pressure of the second expanded beads over time, it is preferable to carry out the filling step during a period when the internal pressure of the second expanded beads becomes an internal pressure suitable for molding during expansion molding. When the expanded beads are used as a raw material, there is an advantage in that there is a large time lag between the pressurization step and the filling step.

[0123] In the filling step, the mold does not need to be closed, and a small gap (also called cracking) may be formed between the fixed mold and the movable mold. The cracking (mm) is not particularly limited, and may be, for example, more than 0.0 mm and not more than 20.0 mm, 1.0 mm to 10.0 mm, or 1.0 mm to 4.0 mm.

[0124] The method for filling the foamed beads into the molding space of the mold to which internal pressure has been applied is not particularly limited, and the foamed beads can be filled, for example, through a known filling machine.

[0125] (Foam molding process) The foam molding step can also be said to be a step for obtaining a foam molded article.

[0126] If the mold has cracks during the filling process, the moving mold is driven toward the fixed mold so that the mold is completely closed during the foam molding process.

[0127] In the expansion molding process, the method for fusing the expanded beads is not particularly limited. For example, the expanded beads can be fused by preheating the mold with steam, then heating the mold with steam in one direction and in the opposite direction, and then heating the mold on both sides with steam. Here, the "steam pressure during one-way heating and in the opposite direction heating" is referred to as "steam pressure A," and the "steam pressure during double-sided heating" is referred to as "steam pressure B."

[0128] The steam pressure A is not particularly limited, but is preferably 0.01 MPa (gauge pressure) to 0.15 MPa (gauge pressure), more preferably 0.02 MPa (gauge pressure) to 0.13 MPa (gauge pressure), and even more preferably 0.04 MPa (gauge pressure) to 0.13 MPa (gauge pressure). This configuration has the advantage that a foamed molded article with a high internal fusion rate tends to be obtained.

[0129] The water vapor pressure B is preferably 0.20 MPa (gauge pressure) or less, more preferably 0.19 MPa (gauge pressure) or less, even more preferably 0.16 MPa (gauge pressure) or less, and even more preferably 0.14 MPa (gauge pressure) or less. The lower the water vapor pressure B, the smaller the economic burden. There are no particular restrictions on the lower limit of the water vapor pressure B, but it is preferably 0.05 MPa (gauge pressure) or more, and more preferably 0.09 MPa (gauge pressure) or more. When the lower limit of the water vapor pressure B is within the above-mentioned range, there is an advantage that a foamed molded article having excellent internal fusion rate and impact resistance tends to be obtained.

[0130] (Productivity) In this specification, the productivity of the method for producing a P3HA-based foam molded article according to one embodiment of the present invention is evaluated by the length of the molding cycle, which refers to the time (seconds) required from the moment the movable mold starts to move toward the fixed mold so that the mold is completely closed in the foam molding process until the foam molded article is completely removed from the mold.

[0131] In the method for producing a P3HA-based foam molded article according to one embodiment of the present invention, the molding cycle is preferably 180 seconds or less, more preferably 175 seconds or less, even more preferably 170 seconds or less, even more preferably 165 seconds or less, and particularly preferably 160 seconds or less. When the molding cycle is 180 seconds or less, foam molded articles can be provided with high production efficiency. [Example]

[0132] 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.

[0133] 〔material〕 The substances used in the examples and comparative examples are shown below.

[0134] (Poly(3-hydroxyalkanoate)) P3HA-1: P3HA-1 is P3HB3HH (monomer ratio: 3HB / 3HH = 95 / 5 (mol% / mol%), melting point: 145°C) and was prepared in accordance with the method described in Example 1 of International Publication WO2021 / 085534.

[0135] (nucleating agent) Pentaerythritol (Mitsubishi Chemical NeuRizer P) (Foam adjuster) Talc (Hayashi Kasei Talc Powder PK-S) (lubricant) Behenamide (Nippon Fine Chemicals, BNT-22H) Erucic acid amide (Neutron-S, manufactured by Nippon Fine Chemicals) (foaming agent) Carbon dioxide (manufactured by Air Water Inc.) Nitrogen (manufactured by Air Water Inc.) (Crosslinking agent) t-Butylperoxy-2-ethylhexyl monocarbonate (TBEC: Perbutyl E manufactured by NOF Corporation) (dispersant) Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.) (Dispersion aid) Sodium alkanesulfonate (Latemul PS manufactured by Kao Corporation).

[0136] [Measurement method] The evaluation methods used in the examples and comparative examples are described below.

[0137] (internal pressure of foam particles) The internal pressure of the expanded beads was measured by the following methods (1) to (5): (1) the weight W1 (g) of the expanded beads after the pressurization step was measured; (2) the expanded beads were heated at 150°C for 30 minutes to allow the inorganic gas inside the expanded beads to dissipate; (3) the weight W2 (g) of the expanded beads from which the inorganic gas had dissipated was measured again; (4) the weight of the inorganic gas (ΔW) was calculated from the difference in weight (W1 - W2) of the expanded beads before and after the inorganic gas had dissipated; (5) the internal pressure P (MPa (absolute pressure)) of the expanded beads was calculated using the equation of state of an ideal gas (specifically, the following formula): Internal pressure of foam particles P (MPa (absolute pressure)) = (1 + ΔW / 28.8 × 0.082 × (273 + T) × (ρ × 1000 / W2)) / 9.87 In the above formula, T is the temperature (room temperature) when the weight of the expanded beads after the pressurizing step is measured, and ρ is the apparent density (g / cc) of the expanded beads after the pressurizing step (expanded beads with a weight W1).

[0138] The apparent density of the expanded beads (expanded beads after pressurization) was measured using the following methods (1) to (3): (1) A measuring cylinder containing ethanol was prepared, and expanded beads with a weight Wd (g) were submerged in the ethanol; (2) The volume of the expanded beads determined from the rise in the water level of the ethanol (submersion method) was defined as Vd (cc); (3) The apparent density of the expanded beads was calculated using the following formula: Apparent density (g / cc) = Wd / Vd.

[0139] (Open cell ratio of foamed beads) First, the volume of the foamed particles, Vc (cm), was measured in accordance with the method described in Procedure C of ASTM D2856-87. 3Next, the entire amount of the expanded beads after measuring the volume Vc was submerged in a measuring cylinder containing ethanol, and the apparent volume Va (cm) of the expanded beads was calculated from the rise in the water level in the measuring cylinder (submersion method). 3 The open cell ratio of the expanded beads was calculated from the formula (Va-Vc) / Va×100(%).

[0140] (Surface beauty of foam molded products) The evaluation method for the surface aesthetics of the foamed molded article was as follows: the surface of the foamed molded article was visually observed, and the surface aesthetics was evaluated based on the following criteria: ◯ (Good): There are no sink marks, wrinkles, or gaps between particles on the surface of the foamed molded article, and the surface irregularities are not noticeable. × (Poor): One or more of sink marks, wrinkles, and gaps between particles are present on the surface of the foamed molded article, and / or the surface is noticeably uneven.

[0141] (Internal fusion rate of foam molded body) The internal fusion rate was measured by the following methods (1) to (4): (1) a cutter was used to make a vertical incision on the surface of the foamed molded article, measuring 1 / 20 to 1 / 5 of the thickness (50 mm); (2) the foamed molded article was then manually broken along the incision; (3) an area of ​​45 mm length (thickness direction) x 90 mm width, excluding the incision, of the resulting fracture surface was visually observed, and the number of all foamed beads present within that area and the number of foamed beads within that area that were broken other than at the particle interface (i.e., foamed beads where the foamed beads themselves were broken) were counted; (4) the internal fusion rate was calculated using the following formula: Internal fusion rate (%) = (number of expanded particles broken at locations other than particle interfaces within the above-mentioned range of 45 mm length (thickness direction) × 90 mm width / total number of expanded particles within the above-mentioned range) × 100.

[0142] (Shrinkage rate of foam molded product) The methods for measuring and evaluating the shrinkage rate of the foam molded product were as follows (1) to (3): (1) The length t (mm) of the foam molded product in the longitudinal direction was measured; (2) The length K (mm) of the foam molded product in the molding space of the mold used for in-mold foam molding in the direction corresponding to the longitudinal direction of the foam molded product was measured; (3) The shrinkage rate of the foam molded product was calculated according to the following formula: Shrinkage rate (%) = {(Kt) / K} × 100.

[0143] [Production Example 1] (Production of first expanded beads) (Resin particle manufacturing process) A twin-screw extruder (TEM-26SX, manufactured by Toshiba Machine Co., Ltd.) was used to melt-knead the P3HA-based composition. 100 parts by weight of P3HA-1, 1.0 part by weight of pentaerythritol as a nucleating agent, 0.10 part by weight of talc as a cell control agent, and 0.10 parts by weight of behenamide and 0.10 parts by weight of erucamide as lubricants were weighed and dry-blended to prepare the P3HA-based composition. The prepared P3HA-based composition was fed into the twin-screw extruder, and melt-kneaded at a cylinder temperature of 130°C to 160°C (melt-kneading step). The melt-kneaded P3HA-based composition at 180°C was extruded from the 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).

[0144] (Foaming process) 100 parts by weight of the P3HA-based resin particles obtained in the resin particle production process described above, 2.0 parts by weight of TBEC as a crosslinking agent, 350 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.

[0145] Nitrogen was introduced into the pressure vessel, and a vacuum was created to remove oxygen from the pressure vessel. Carbon dioxide was then supplied as a blowing agent into the pressure vessel to prepare a dispersion (dispersion process). The temperature inside the pressure vessel was then raised to the foaming temperature of 129°C. Carbon dioxide was then supplied to the pressure vessel to raise the pressure inside the pressure vessel to a foaming pressure of 3.3 MPa (gauge pressure) (temperature-pressure increase process). The temperature and pressure inside the pressure vessel were then maintained near the foaming temperature and foaming pressure, respectively, for 60 minutes (holding process). After the holding process, the valve at the bottom of the pressure vessel was opened, and the dispersion in the pressure vessel was released into atmospheric pressure through a 3.6 mm diameter orifice, yielding first P3HA-based expanded beads (release process). The dispersant and other substances adhering to the surface of the expanded beads were washed with water, and the first expanded beads were then dried at 75°C.

[0146] Example 1 (Pressure process) A pressure-resistant vessel equipped with a discharge section was used as the vessel. The discharge section included (i) a valve installed midway through the piping and (ii) a discharge port with a diameter of 2.8 cm and a circular cross-sectional shape. The first expanded beads were supplied to the pressure-resistant vessel at 80°C. While the temperature inside the pressure-resistant vessel was maintained at 80°C, air was introduced into the pressure-resistant vessel to increase the pressure inside the pressure-resistant vessel to a pressure higher than the set pressure listed in Table 1. Next, the pressure inside the pressure-resistant vessel was reduced to the "set pressure" listed in Table 1 at a rate of 0.02 MPa / hr by releasing air from the pressure-resistant vessel, and the temperature inside the pressure-resistant vessel was then decreased to the "container temperature at pressure release" listed in Table 1. Through these operations, the first expanded beads were pressurized so that the internal pressure of the first expanded beads reached the pressure listed in "Immediately after the discharge step" under "Internal pressure of expanded beads (absolute pressure)" in Table 1. The pressure described in "immediately after the discharging step" is a value obtained by measuring the internal pressure of the second expanded beads obtained in the discharging step using the method described above.

[0147] (Discharge process) After the pressurization step, the pressure in the pressure-resistant container was released by opening the valve of the dispensing section, and the first expanded beads were discharged from the container through the dispensing port to obtain second expanded beads. After the amount of first expanded beads required for molding was discharged from the dispensing port, the valve was immediately closed. The pressure release conditions for the dispensing step are shown in Table 1. In Examples 1 and 6, the area of ​​the pressure release port was the area of ​​the dispensing port of the dispensing section. In all Examples and Comparative Examples, the "pressure release rate" and "pressure release port area" in Table 1 were calculated by rounding to the fifth decimal place and the second decimal place, respectively, for convenience, and the results are shown here.

[0148] Examples 2 and 3 (Pressure process) A pressure-resistant vessel equipped with a pressure release part and a manhole was used as the vessel. The pressure release part had (i) a valve installed midway through the pipe and (ii) an opening with a diameter of 2.8 cm and a circular cross-sectional shape. The first expanded beads were supplied to the pressure-resistant vessel at 80°C. While the temperature inside the pressure-resistant vessel was maintained at 80°C, air was introduced into the pressure-resistant vessel to increase the pressure inside the pressure-resistant vessel to the "set pressure" listed in Table 1. By this operation, the first expanded beads were pressurized so that the internal pressure of the first expanded beads reached the pressure listed in "Immediately after the dispensing process" under "Internal pressure of expanded beads (absolute pressure)" in Table 1.

[0149] (Discharge process) After the pressurization step, the temperature inside the pressure vessel was lowered to the "Temperature inside the vessel at the time of pressure release" shown in Table 1. Next, the valve of the pressure release section was opened to release the pressure inside the pressure vessel to atmospheric pressure at the "Pressure Release Rate" shown in Table 1. After the pressure inside the pressure vessel was released, the first expanded beads were taken out through the manhole to obtain second expanded beads. The pressure release conditions in the discharging step are shown in Table 1. In Examples 2 and 3, the area of ​​the pressure release port was the area of ​​the opening of the pressure release section.

[0150] Examples 4 and 5 (Pressure process) A pressure-resistant vessel equipped with a discharge section was used as the vessel. The discharge section had (i) a valve installed midway through the piping and (ii) a discharge port with a diameter of 5.5 cm and a circular cross-sectional shape. The first expanded beads were supplied to the pressure-resistant vessel at 80°C. While the temperature inside the pressure-resistant vessel was maintained at 80°C, air was introduced into the pressure-resistant vessel to increase the pressure inside the pressure-resistant vessel to the "set pressure" listed in Table 1. By this operation, the first expanded beads were pressurized so that the internal pressure of the first expanded beads reached the pressure listed in "Immediately after the discharge process" under "Internal pressure of expanded beads (absolute pressure)" in Table 1.

[0151] (Discharge process) After the pressurization step, the temperature inside the pressure vessel was lowered to the "temperature inside the vessel at the time of pressure release" shown in Table 1. Next, the pressure inside the pressure vessel was released by opening the valve of the dispensing section, and the first expanded beads were discharged from the vessel through the dispensing port to obtain second expanded beads. After the amount of first expanded beads required for molding was discharged from the dispensing port, the valve was immediately closed. The conditions for pressure release in the dispensing step are shown in Table 1. In Examples 4 and 5, the area of ​​the pressure release port was the area of ​​the dispensing port of the dispensing section.

[0152] Example 6 (Pressure process) A pressure-resistant vessel equipped with a discharge part was used as the vessel. The discharge part was equipped with (i) a valve installed midway through the piping, and (ii) a discharge port with a diameter of 5.5 cm and a circular cross-sectional shape. Except for this, the pressurization step was carried out in the same manner as in Example 1.

[0153] (Discharge process) The discharging step was carried out in the same manner as in Example 1 to obtain second expanded beads. The conditions for releasing pressure in the discharging step are shown in Table 1.

[0154] Examples 7 and 8 (Pressure process) A pressure-resistant vessel equipped with a pressure release part and a manhole was used. The pressure release part had (i) a valve installed midway through the pipe, and (ii) an opening with a diameter of 5.0 cm and a circular cross-sectional shape. Other than that, the pressurization step was carried out in the same manner as in Example 2.

[0155] (Discharge process) The discharging step was carried out in the same manner as in Example 2 to obtain second expanded beads, except that the pressure release rate was changed to the "pressure release rate" in Table 1. The conditions for pressure release in the discharging step are shown in Table 1.

[0156] (Comparative Example 1) The pressurizing step and the expelling step were carried out in the same manner as in Example 1 to obtain second expanded beads. The conditions for releasing the pressure in the expelling step are shown in Table 1.

[0157] (Comparative Example 2) (Pressure process) A pressure-resistant vessel equipped with a discharge part was used as the vessel. The discharge part was equipped with (i) a valve installed midway through the piping, and (ii) a discharge port with a diameter of 2.8 cm and a circular cross-sectional shape. Other than that, the pressurization step was carried out in the same manner as in Example 4.

[0158] (Discharge process) The discharging step was carried out in the same manner as in Example 4 to obtain second expanded beads. The conditions for releasing pressure in the discharging step are shown in Table 1.

[0159] (Production of foam molded products) The second expanded beads obtained in Examples 1 to 8 and Comparative Examples 1 and 2 were used to produce (molded) foamed molded articles by the following method. A mold having a molding space of 370 mm length x 320 mm width x 50 mm thickness mounted on a molding machine (EP-900 manufactured by DAISEN) was used. The molding space of the mold, with a cracking of 3.0 mm, was filled with the second expanded beads using a filling machine (filling step).

[0160] Next, the movable mold was driven toward the fixed mold, and after the mold was completely closed, the mold was preheated with steam. The mold was then heated in one direction and reverse direction with steam, and then heated on both sides with steam. These operations fused the filled second foam particles to obtain a foamed molded article (foam molding process). The steam pressure during one direction and reverse direction heating (steam pressure A) was 0.06 MPa (gauge pressure), and the steam pressure during double-sided heating (steam pressure B) was 0.13 MPa (gauge pressure). The resulting foamed molded article was removed from the mold and dried at 75°C. The surface appearance, internal fusion rate, and shrinkage rate of the dried foamed molded article were measured and evaluated. The results are shown in Table 1.

[0161] [Table 1] [Industrial Applicability]

[0162] According to one embodiment of the present invention, poly(3-hydroxyalkanoate)-based expanded particles having a low open cell content can be provided. The expanded molded articles can be suitably used for food containers, packaging materials, sanitary goods, garbage bags, cushioning materials for packaging, agricultural product boxes, fish boxes, automotive components, building materials, civil engineering materials, etc.

Claims

1. a pressurizing step of supplying first poly(3-hydroxyalkanoate)-based expanded beads into a container and pressurizing the first poly(3-hydroxyalkanoate)-based expanded beads; a discharging step of discharging the first poly(3-hydroxyalkanoate)-based expanded beads from the container while releasing the pressure in the container or after releasing the pressure in the container, In the discharging step, the pressure in the container is released so as to satisfy the following formula (1): Pressure release speed (MPa / sec) × pressure inside the container at the time of pressure release (gauge pressure) (MPa) / area of ​​the pressure release port (m ２ )<10.00... Formula (1).

2. The pressurizing step includes:

2. The method for producing the second poly(3-hydroxyalkanoate)-based expanded beads according to claim 1, wherein the first poly(3-hydroxyalkanoate)-based expanded beads are pressurized so that the pressure (absolute pressure) inside the second poly(3-hydroxyalkanoate)-based expanded beads is 0.12 MPa to 0.35 MPa.

3. 3. The second method for producing expanded poly(3-hydroxyalkanoate)-based beads according to claim 1, wherein the pressure release rate is 0.0001 MPa / sec to 0.0350 MPa / sec.

4. 4. The method for producing the second poly(3-hydroxyalkanoate)-based expanded beads according to claim 1, wherein the pressure (gauge pressure) inside the container when the pressure is released is 0.04 MPa to 0.50 MPa.

5. The area of ​​the pressure release port is 0.0005 m ２ ~0.0100m ２ The method for producing the second expanded poly(3-hydroxyalkanoate) beads according to any one of claims 1 to 4,

6. 6. The method for producing the second expanded poly(3-hydroxyalkanoate) beads according to claim 1, wherein the temperature inside the container when the pressure is released in the discharging step is 10°C to 60°C.

7. The method for producing the second poly(3-hydroxyalkanoate)-based expanded beads according to any one of claims 1 to 6, wherein the first poly(3-hydroxyalkanoate)-based expanded beads are crosslinked with an organic peroxide.

8. 8. The second method for producing expanded poly(3-hydroxyalkanoate)-based beads according to claim 7, wherein the organic peroxide has a t-butoxy group and / or a cumyloxy group.

9. A method for producing a poly(3-hydroxyalkanoate)-based expanded molded article, comprising a step of molding the second poly(3-hydroxyalkanoate)-based expanded beads produced by the second method for producing poly(3-hydroxyalkanoate)-based expanded beads according to any one of claims 1 to 8.

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