JP7819005B2 - Poly(3-hydroxyalkanoate)-based expanded particles and poly(3-hydroxyalkanoate)-based expanded molded articles - Google Patents

Description

The present invention relates to expanded poly(3-hydroxyalkanoate) beads and expanded poly(3-hydroxyalkanoate) molded articles.

Large quantities 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 also become a major problem in the marine environment. For this reason, biodegradable plastics that are decomposed by the action of microorganisms in (a) the ocean, soil, and other environments, and (b) landfills and compost, have attracted attention. Development of biodegradable plastics is underway with the aim of achieving 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 products that are difficult to recover and reuse after use. Furthermore, foams made from biodegradable plastics are expected to be used in packaging cushioning, agricultural product boxes, fish boxes, automotive components, building materials, civil engineering materials, and more.

Among the biodegradable plastics, poly(3-hydroxyalkanoate) resins (hereinafter sometimes referred to as "P3HA resins") derived from plant materials have attracted attention due to their excellent biodegradability and carbon neutrality, and the use of these P3HA resins in molded articles is being investigated.

Patent Document 1 discloses poly(3-hydroxyalkanoate)-based expanded beads (hereinafter sometimes referred to as "P3HA-based expanded beads") that have a heat of fusion on the high-temperature side of a specific range, and a technique for in-mold foaming of the P3HA-based expanded beads to obtain a poly(3-hydroxyalkanoate)-based expanded molded article (hereinafter sometimes referred to as "P3HA-based expanded molded article"). Furthermore, Patent Document 2 discloses a technique for in-mold foaming of biodegradable polyester-based resin expanded beads that contain a biodegradable polyester-based resin in a specific crystalline state to obtain a foamed molded article.

International Publication No. 2019/146555 International Publication No. 2020/201935

The above-mentioned technology is excellent, but there is room for improvement in terms of the stability of the production of P3HA-based expanded beads that have a heat of fusion on the higher end of a specific range.

In light of the above circumstances, an object of one embodiment of the present invention is to provide P3HA-based expanded beads that have the desired high-temperature heat of fusion and can be produced stably.

The inventors conducted extensive research to solve the above problems, and as a result, they have completed the present invention.

That is, one embodiment of the present invention includes the following configuration.
[1] Expanded poly(3-hydroxyalkanoate)-based particles obtained by expanding poly(3-hydroxyalkanoate)-based resin particles containing a poly(3-hydroxyalkanoate)-based resin composition, wherein the poly(3-hydroxyalkanoate)-based resin particles have a DSC curve obtained by differential scanning calorimetry, in which the difference between the melting peak temperature and the melting end temperature is 8°C to 20°C, and the heat of fusion at temperatures equal to or higher than the melting peak temperature is 5 J/g to 15 J/g.
[2] The poly(3-hydroxyalkanoate)-based expanded particles according to [1], wherein the poly(3-hydroxyalkanoate)-based resin composition contains two or more types of poly(3-hydroxyalkanoate)-based resins having different constitutional unit compositions.
[3] The poly(3-hydroxyalkanoate)-based expanded particles according to [1] or [2], wherein the poly(3-hydroxyalkanoate)-based resin composition contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate).
[4] The poly(3-hydroxyalkanoate) resin composition comprises P3HB3HH(A) and P3HB3HH(B), each of which comprises a 3-hydroxybutyrate unit (3HB unit) and a 3-hydroxyhexanoate unit (3HH unit), and the ratio of the 3HB unit to the 3HH unit (3HB unit/3HH unit) in 100 mol% of all repeating units in the P3HB3HH(A) is 98.0/2.0 (mol%/mol%) to 94.0/6.0 (mol%). mol%/mol%), the ratio of 3HB units to 3HH units (3HB units/3HH units) in 100 mol% of all repeating units in the P3HB3HH(B) is 93.9/6.1 (mol%/mol%) to 90.0/10.0 (mol%/mol%), and the weight ratio of P3HB3HH(A) to P3HB3HH(B) (weight of P3HB3HH(A)/weight of P3HB3HH(B)) is 90/10 (wt%) to 10/90 (wt%).
[5] The expanded poly(3-hydroxyalkanoate)-based beads according to any one of [1] to [4], wherein the expanded poly(3-hydroxyalkanoate)-based beads have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry.
[6] The expanded poly(3-hydroxyalkanoate) beads according to [5], wherein the DSC curve obtained by differential scanning calorimetry shows at least two melting peaks, the highest of which has a heat of fusion of 0.1 J/g to 20.0 J/g. [7] A poly(3-hydroxyalkanoate) foamed molded article obtained by molding the expanded poly(3-hydroxyalkanoate) beads according to any one of [1] to [6].

One embodiment of the present invention has the effect of providing P3HA-based expanded beads that have the desired high-temperature heat of fusion and can be produced stably.

FIG. 1 is a diagram showing an example of a DSC curve obtained by differential scanning calorimetry of P3HA-based resin particles.

One embodiment of the present invention is described below, but the present invention is not limited to this. The present invention is not limited to the 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 created by combining the technical means disclosed in each embodiment. All academic and patent literature described in this specification is incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the expression "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)."

1. Technical Concept of the Present Invention
Patent Document 1 reports that P3HA-based expanded beads have at least two melting peaks in a DSC curve, and that the heat of fusion on the higher temperature side (the heat of fusion of the melting peak on the higher temperature side) is an important parameter related to the in-mold foamability of the resulting P3HA-based expanded beads and the properties of the foamed molded article (e.g., surface properties, shrinkage suppression, etc.).

It is known that the heat of fusion at the high temperature side of P3HA-based expanded beads can be controlled by adjusting conditions such as the expansion temperature and holding time during the expansion process. However, the inventors have newly discovered that with conventional P3HA-based expanded beads such as those described in Patent Document 1, if the expansion temperature and/or holding time conditions change (e.g., if the expansion temperature changes by approximately 1°C), the heat of fusion at the high temperature side of the resulting P3HA-based expanded beads changes significantly, making it impossible to produce P3HA-based expanded beads with the desired heat of fusion at the high temperature side. In other words, the inventors have newly discovered that the allowable range (process window) for the expansion temperature and holding time during the expansion process for producing P3HA-based expanded beads with the desired heat of fusion at the high temperature side is extremely narrow. In particular, in large-scale industrial production, it is extremely difficult to maintain a constant expansion temperature and holding time for each individual expanded bead. That is, conventional P3HA-based expanded beads such as those described in Patent Document 1 have the problem that it is difficult to stably produce (especially industrially produce) P3HA-based expanded beads having the desired high-temperature heat of fusion.

In light of the above circumstances, the inventors conducted extensive research with the aim of providing poly(3-hydroxyalkanoate)-based expanded beads that have the desired high-temperature heat of fusion and can be produced stably.

After extensive research, the inventors independently discovered the following, leading to the completion of the present invention: Poly(3-hydroxyalkanoate)-based resin particles (hereinafter sometimes referred to as "P3HA-based resin particles"), in which the difference between the melting peak temperature and the melting end temperature in a DSC curve obtained by differential scanning calorimetry is within a specific range and the heat of fusion above the melting peak temperature is within a specific range, have a wide process window for the expansion temperature and holding time in the expansion process. Therefore, in the production of P3HA-based expanded beads using these P3HA-based resin particles, changes in the heat of fusion on the high-temperature side of the resulting P3HA-based expanded beads due to changes in the expansion temperature and holding time during the expansion process are suppressed. As a result, the P3HA-based expanded beads obtained by expanding these P3HA-based resin particles have the desired heat of fusion on the high-temperature side and can be produced stably.

Furthermore, P3HA-based expanded beads according to one embodiment of the present invention, which contain the biodegradable P3HA-based resin, and P3HA-based expanded molded articles obtained by molding the P3HA-based expanded beads, can reduce marine pollution caused by waste disposal. This can contribute to the achievement of Sustainable Development Goals (SDGs), such as Goal 12 "Ensure sustainable consumption and production patterns" and Goal 14 "Conserve and sustainably use the oceans and marine resources for sustainable development."

2. Poly(3-hydroxyalkanoate)-based expanded particles
The expanded poly(3-hydroxyalkanoate)-based particles according to one embodiment of the present invention are poly(3-hydroxyalkanoate)-based particles obtained by expanding poly(3-hydroxyalkanoate)-based resin particles containing a poly(3-hydroxyalkanoate)-based resin composition, and the poly(3-hydroxyalkanoate)-based resin particles have a DSC curve obtained by differential scanning calorimetry, in which the difference between the melting peak temperature and the melting end temperature is 8°C to 20°C, and the heat of fusion at temperatures equal to or higher than the melting peak temperature is 5 J/g to 15 J/g.

In this specification, "poly(3-hydroxyalkanoate) (P3HA)-based expanded particles" may be referred to as "expanded particles," "poly(3-hydroxyalkanoate) (P3HA)-based resin particles" may be referred to as "resin particles," "poly(3-hydroxyalkanoate) (P3HA)-based resin composition" may be referred to as "resin composition," and "poly(3-hydroxyalkanoate)-based expanded molded article" may be referred to as "expanded molded article." Furthermore, "poly(3-hydroxyalkanoate) (P3HA)-based expanded particles according to one embodiment of the present invention" may be referred to as "the present expanded particles."

Because the expanded beads have the above-mentioned structure, they have the advantage of having the desired high-temperature heat of fusion and can be produced stably.

In this specification, the phrase "expanded beads have a desired heat of fusion on the high-temperature side" specifically means that the heat of fusion of the highest temperature melting peak in the DSC curve obtained by differential scanning calorimetry of the expanded beads is 0.1 J/g to 20.0 J/g. Expanded beads with such a desired heat of fusion on the high-temperature side can provide foamed molded articles with excellent surface properties and shrinkage suppression.

In this specification, a repeating unit derived from an X monomer may be referred to as an "X unit." A repeating unit can also be referred to as a structural unit.

First, we will explain the resin particles and resin composition that are the raw materials for these expanded beads.

<P3HA-based resin particles>
The present expanded beads are formed by expanding poly(3-hydroxyalkanoate)-based resin particles containing a poly(3-hydroxyalkanoate)-based resin composition. In this specification, a "poly(3-hydroxyalkanoate) (P3HA)-based resin composition according to one embodiment of the present invention" may be referred to as "the present resin composition," and a "poly(3-hydroxyalkanoate) (P3HA)-based resin particle according to one embodiment of the present invention" may be referred to as "the present resin particle." The present resin particle can be provided by granulating the present resin composition using the method described below. Therefore, the type and amount (content) of the P3HA-based resin and other components contained in the present resin particles are the type and amount (content) of the P3HA-based resin and other components contained in the present resin composition.

(P3HA-based resin composition)
The present resin composition preferably contains two or more types of poly(3-hydroxyalkanoate) resins having different constitutional unit compositions.

A resin composition containing two or more P3HA-based resins with different structural unit compositions can suitably provide resin particles in which, in a DSC curve obtained by differential scanning calorimetry, the difference between the melting peak temperature and the melting end temperature is 8°C to 20°C, and the heat of fusion above the melting peak temperature is 5 J/g to 15 J/g. Therefore, this resin composition can more suitably provide expanded beads that have the desired heat of fusion on the high-temperature side and can be produced stably.

In this specification, "different constitutional unit compositions" of P3HA-based resins includes both cases where "the types of constitutional units constituting the P3HA-based resin are different" and cases where "the P3HA-based resin contains two or more types of the same type of constitutional units, but the content ratios (monomer ratios) of those constitutional units are different."

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

In general formula (1), R represents an alkyl group represented by C _n H _2n+1 , where n represents an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as methyl, ethyl, propyl, isopropyl, butyl, isobutyl, t-butyl, pentyl, and hexyl. Furthermore, n is preferably 1 to 10, and more preferably 1 to 8.

P3HA-based resins produced by microorganisms are particularly preferred.

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

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

When a P3HA-based resin contains two or more types of structural units, the monomer from which the structural units other than the structural unit (monomer unit) with the largest content are derived is referred to as a comonomer. In this specification, a "structural unit derived from a comonomer" may also be referred to as a "comonomer unit."

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

The P3HA-based resin may be a polymer (homopolymer) consisting of only one type of structural unit.

Specific examples of P3HA-based resins include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter sometimes referred to as "P3HB3HV"), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "P3HB3HH"). Examples thereof include poly(3-hydroxybutyrate-co-3-hydroxyheptanoate), poly(3-hydroxybutyrate-co-3-hydroxyoctanoate), poly(3-hydroxybutyrate-co-3-hydroxynonanoate), poly(3-hydroxybutyrate-co-3-hydroxydecanoate), poly(3-hydroxybutyrate-co-3-hydroxyundecanoate), and poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter, sometimes referred to as "P3HB4HB"). In particular, from the viewpoints of processability and the physical properties of foamed molded articles, poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred, with poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) being more preferred due to the advantage of providing an excellent balance between the heat resistance and other physical properties (e.g., strength) of the resulting foamed molded articles. In other words, the resin composition preferably contains poly(3-hydroxybutyrate-co-3-hydroxyhexanoate). In this specification, P3HA-based resins with the same name (compound name) are considered to be different types of P3HA-based resins if the content ratios (monomer ratios) of the structural units (monomer units and comonomer units) that make up the P3HA-based resins are different. Therefore, as the two or more P3HA-based resins contained in the resin composition that have different structural unit compositions, only P3HA-based resins with the same name (compound name) but different monomer ratios may be used, or P3HA-based resins with different names may be used in combination.

It is preferable that the P3HA-based resin contains 3HB units as an essential structural unit and also contains comonomer units. That is, the P3HA-based resin is preferably a copolymer containing 3HB units and comonomer units. A case in which the P3HA-based resin contains 3HB units and comonomer units (Case a) will be described. In Case a, the ratio of 3HB units to comonomer units (3HB units/comonomer units) in 100 mol% of all structural units in the P3HA-based resin is preferably 99.0/1.0 (mol%/mol%) to 80.0/20.0 (mol%/mol%), more preferably 98.5/1.5 (mol%/mol%) to 85.0/15.0 (mol%/mol%), and even more preferably 98.0/2.0 (mol%/mol%) to 90.0/10.0 (mol%/mol%). If the ratio of comonomer units to 100 mol% of all structural units of the P3HA resin is 1.0 mol% or more, the melt-mixable temperature range of the P3HA resin and its thermal decomposition temperature range are sufficiently separated, resulting in a wide range of suitable molding processability. On the other hand, if the ratio of comonomer units to 100 mol% of all structural units of the P3HA resin is 20.0 mol% or less, the P3HA resin composition crystallizes quickly during melt-mixing, resulting in high productivity. P3HA resins with such monomer unit ratios can be produced according to methods known to those skilled in the art, such as the method described in International Publication WO 2009/145164.

The ratio of each monomer unit in a P3HA-based resin can be determined by methods known to those skilled in the art, such as the method described in WO 2013/147139.

When the P3HA-based resin is a copolymer containing 3HB units and comonomer units, the comonomer units are preferably 3-hydroxyhexanoate units (3HH units), from the viewpoint of excellent molding processability of the resulting expanded beads. In other words, the resin composition preferably contains P3HB3HH as the P3HA-based resin. The resin composition may contain P3HB3HH and a P3HA-based resin other than P3HB3HH, or may contain P3HB3HH(A) and P3HB3HH(B), which contain 3HB units and 3HH units and have different ratios of the 3HB units to the 3HH units (monomer ratios).

The following describes the case where the resin composition contains P3HB3HH(A) and P3HB3HH(B) (Case b). In Case b, the ratio of 3HB units to 3HH units (3HB units/3HH units) in 100 mol% of all repeating units in the P3HB3HH(A) is preferably 98.0/2.0 (mol%/mol%) to 94.0/6.0 (mol%/mol%), more preferably 97.5/2.5 (mol%/mol%) to 94.5/5.5 (mol%/mol%), and even more preferably 97.0/3.0 (mol%/mol%) to 95.0/5.0 (mol%/mol%). Furthermore, the ratio of 3HB units to 3HH units (3HB units/3HH units) in 100 mol% of all repeating units in P3HB3HH(B) is preferably 93.9/6.1 (mol%/mol%) to 90.0/10.0 (mol%/mol%), more preferably 93.7/6.3 (mol%/mol%) to 90.5/9.5 (mol%/mol%), and even more preferably 93.5/6.5 (mol%/mol%) to 91.0/9.0 (mol%/mol%).

In case b, the weight ratio of P3HB3HH(A) to P3HB3HH(B) (weight of P3HB3HH(A)/weight of P3HB3HH(B)) is preferably 90/10 (wt%/wt%) to 10/90 (wt%/wt%), more preferably 85/15 (wt%/wt%) to 15/85 (wt%/wt%), and even more preferably 80/20 (wt%/wt%) to 20/80 (wt%/wt%).

In case b, by setting the monomer ratio of P3HB3HH(A) to P3HB3HH(B) and the weight ratio of P3HB3HH(A) to P3HB3HH(B) within the above ranges, there is an advantage in that P3HB3HH(A) and P3HB3HH(B) are easily compatible with each other.

In case b, the resin composition may contain a P3HA-based resin other than P3HB3HH(A) and P3HB3HH(B) (other P3HA-based resin). In this case, the weight ratio of P3HB3HH(A) and P3HB3HH(B) to the other P3HA-based resin ((total weight of P3HB3HH(A) and P3HB3HH(B))/weight of the other P3HA-based resin) is preferably 99/1 (wt%/wt%) to 50/50 (wt%/wt%), more preferably 97/3 (wt%/wt%) to 60/40 (wt%/wt%), and even more preferably 95/5 (wt%/wt%) to 70/30 (wt%/wt%). This configuration has the advantage that the physical properties (e.g., strength, heat resistance, etc.) of the resulting foamed molded article can be adjusted within preferred ranges.

(Method for producing P3HA-based resin)
In one embodiment of the present invention, the method for producing the P3HA-based resin 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. As a method for producing a P3HA-based resin using a microorganism, known methods can be applied, but it is preferable that the method include a culture step, a purification step, and a drying step.

The method for culturing the microorganisms that produce P3HA in the culturing step is not particularly limited, and for example, the method described in International Publication No. WO2019/142717 can be used.

The method for purifying the P3HA obtained by microbial culture in the purification step is not particularly limited, and known physical and/or chemical and/or biological treatments can be applied. For example, the purification method described in WO 2010/067543 can be preferably applied as a method for purifying P3HA.

The method for drying the P3HA obtained by microbial culture and purification in the drying process is not particularly limited, and spray drying, fluidized bed drying, flash drying, rotary drying, vibration drying, and band drying can be applied. For example, the drying method described in WO 2018/070492 is preferably used as a method for drying P3HA.

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

The resin composition may further contain resin components other than the P3HA-based resin (sometimes referred to as "other resin components"). Examples of other resin components include (a) aliphatic polyesters such as polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone, or (b) aliphatic aromatic polyesters. These other resin components may be used alone or in combination with the P3HA-based resin.

The content of other resin components in this resin composition is not particularly limited, but for example, it is preferably 10 to 400 parts by weight, and more preferably 50 to 150 parts by weight, per 100 parts by weight of P3HA-based resin.

The resin composition may further contain additives.

(Additives)
The resin composition may further contain additives. Examples of additives that can be used depending on the purpose include nucleating agents, cell regulators, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, crosslinking agents, antioxidants, ultraviolet absorbers, colorants, inorganic fillers, organic fillers, and hydrolysis inhibitors. Biodegradable additives are particularly preferred as the additives.

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

The content of the nucleating agent in the resin composition is not particularly limited. The content of the nucleating agent is, for example, preferably 5.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 1.5 parts by weight or less, per 100 parts by weight of the resin composition. There is no particular lower limit to the content of the nucleating agent in the resin composition, but it can be, for example, 0.1 parts by weight or more, per 100 parts by weight of the resin composition.

Examples of foam regulators include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, baking soda, alumina, barium sulfate, aluminum oxide, and bentonite. Among these foam regulators, talc is preferred because of its particularly excellent dispersibility in P3HA. One of these foam regulators may be used alone, or two or more may be mixed and used. When two or more foam regulators are mixed, the mixing ratio may be adjusted appropriately depending on the purpose.

The content of the cell control agent in the resin composition is not particularly limited, but is preferably 0.01 to 1.00 parts by weight, more preferably 0.03 to 0.50 parts by weight, and even more preferably 0.05 to 0.30 parts by weight, per 100 parts by weight of the resin composition.

Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid. Among these, behenamide and erucamide are preferred due to their particularly excellent lubricating effect on P3HA. The amount of lubricant used is not particularly limited, but is preferably 0.01 to 5.00 parts by weight, more preferably 0.05 to 3.00 parts by weight, and even more preferably 0.10 to 1.50 parts by weight, per 100 parts by weight of the resin composition. Furthermore, lubricants may be used singly or in combination, and the mixing ratio can be adjusted appropriately depending on the purpose.

<Physical properties of resin particles>
(Difference between the peak melting temperature and the end temperature of melting of resin particles, and the heat of fusion above the peak melting temperature)
The resin particles have a DSC curve obtained by differential scanning calorimetry, in which the difference between the peak melting temperature and the end melting temperature is 8°C to 20°C, and the heat of fusion at or above the peak melting temperature is 5 J/g to 15 J/g. Expanded beads obtained by expanding resin particles whose difference between the peak melting temperature and the end melting temperature and whose heat of fusion at or above the peak melting temperature are within the above ranges have a desired heat of fusion on the high-temperature side and can be produced stably.

The difference between the peak melting temperature and the end melting temperature of the resin particles may be between 8°C and 20°C, but is preferably between 9°C and 19°C, more preferably between 10°C and 18°C, and even more preferably between 10°C and 17°C.

Furthermore, the heat of fusion of the resin particles at temperatures above their melting peak temperature may be 5 J/g to 15 J/g, but is preferably 5 J/g to 14 J/g, more preferably 5 J/g to 13 J/g, and even more preferably 5 J/g to 12 J/g.

The difference between the melting peak temperature and the melting end temperature of the resin particles, and the heat of fusion above the melting peak temperature, can be calculated based on a DSC curve obtained using a differential scanning calorimeter (e.g., DSC7020 manufactured by Hitachi High-Tech Science Corporation) with the resin particles as a sample.

The method for measuring the difference between the melting peak temperature and the melting end temperature of resin particles using a differential scanning calorimeter will be explained in more detail with reference to Figure 1. Figure 1 shows an example of a DSC curve obtained by differential scanning calorimetry for P3HA-based resin particles. The method for measuring the difference between the melting peak temperature and the melting end temperature of resin particles is as follows (1) to (3): (1) weigh out approximately 5 mg of resin particles; (2) use a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation) to measure the temperature of the resin particles from 10°C to 190°C at a heating rate of 10°C/min. The DSC curve obtained is then used to measure the highest melting peak temperature (Tmp) (see Figure 1); (3) the temperature at the end of melting is measured as the melting end temperature (Tme), and the difference between the measured Tmp and Tme (Tme - Tmp) is the difference between the melting peak temperature and the melting end temperature (ΔTrp) of the resin particles. The melting peak temperature (Tmp) of the resin particles can also be considered the melting point of the resin particles.

The method for measuring the heat of fusion above the melting peak temperature of resin particles using a differential scanning calorimeter will now be explained in more detail, again with reference to Figure 1. The heat of fusion above the melting peak temperature of the resin particles is measured using the following methods (1) to (5): (1) weigh out approximately 5 mg of resin particles; (2) use a differential scanning calorimeter (Hitachi High-Tech Science DSC7020) to raise the temperature of the resin particles from 10°C to 190°C at a heating rate of 10°C/min to melt the resin particles; (3) create a baseline on the DSC curve obtained in step (2) by connecting the point representing the melting start temperature with the point representing the melting end temperature (Tme) with a straight line (see Figure 1); (4) draw a line passing through the highest temperature melting peak perpendicular to the X-axis (temperature axis); (5) calculate the heat of fusion from the higher temperature region (the shaded area in Figure 1) within the region surrounded by the baseline, the line passing through the melting peak, and the DSC curve, and determine the heat of fusion above the melting peak temperature of the resin particles.

(MFR of resin particles)
The melt flow rate (MFR) of the resin particles is not particularly limited, but is preferably 1.0 g/10 min to 20.0 g/10 min, more preferably 1.5 g/10 min to 15.0 g/10 min, and even more preferably 2.0 g/10 min to 10.0 g/10 min. MFR is sometimes also referred to as "melt index (MI)."

When the MFR of the resin particles is 1.0 g/10 min or more, the apparent density of the resulting expanded beads tends to be low. When the MFR of the resin particles is 20.0 g/10 min or less, the gel fraction of the resulting expanded beads tends to be high.

In this specification, the MFR of resin particles is a value obtained by measurement using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7210, under conditions of a load of 5 kg and a measurement temperature of +1°C to +10°C above the melting end temperature of the resin particles, which can be read from the DSC curve of the resin particles obtained using a differential scanning calorimeter (e.g., DSC7020 manufactured by Hitachi High-Tech Science Corporation).

<Physical properties of expanded beads>
(Heat of fusion of the highest temperature melting peak of the expanded beads)
The expanded beads have a heat of fusion of their highest temperature peak of preferably 0.1 J/g to 20.0 J/g, more preferably 0.3 J/g to 18.0 J/g, even more preferably 0.5 J/g to 16.0 J/g, and even more preferably 1.0 J/g to 14.0 J/g. Expanded beads having a heat of fusion of their highest temperature peak within the above range can provide foamed molded articles with excellent surface properties and shrinkage suppression.

The method for measuring the heat of fusion above the melting peak temperature of the expanded beads is as follows (1) to (5): (1) weigh out approximately 5 mg of expanded beads; (2) use a differential scanning calorimeter (DSC7020, manufactured by Hitachi High-Tech Science Corporation) to raise the temperature of the expanded beads from 10°C to 190°C at a heating rate of 10°C/min to melt the expanded beads; (3) create a baseline on the DSC curve obtained in step (2) by connecting the point representing the melting start temperature with the point representing the melting end temperature; (4) draw a line passing through the maximum point between the highest temperature melting peak and the melting peak adjacent to the highest temperature melting peak (a line passing through the maximum point) perpendicular to the X-axis (temperature axis); (5) the heat of fusion above the melting peak temperature (MEfp) is calculated from the highest temperature region of the region surrounded by the created baseline, the line passing through the maximum point, and the DSC curve.

(Number of melting peaks of expanded beads)
The expanded beads preferably have at least two melting peaks in the DSC curve obtained in step (2) above. The fact that the expanded beads have at least two melting peaks in the DSC curve obtained by differential scanning calorimetry means that the P3HA resin contained in the expanded beads is in a suitable crystalline state, and such expanded beads are preferred because they have excellent in-mold foaming moldability, and further, foamed molded articles obtained by molding such expanded beads have excellent physical properties (e.g., strength, heat resistance).

(Temperature Dependence of Heat of Fusion of the Highest Temperature Melting Peak of Expanded Beads)
Whether expanded beads "have a desired heat of fusion on the high-temperature side and can be stably produced" can be evaluated by measuring the temperature dependence of the heat of fusion of the highest-temperature melting peak of the expanded beads (hereinafter sometimes referred to as "temperature dependence of expanded beads"). The temperature dependence of expanded beads can be calculated as the difference (amount of change per 1°C) between the "heat of fusion of the highest-temperature melting peak" of expanded beads (comparison expanded beads) obtained by expanding the resin particles used as the raw material for the expanded beads to be measured under the same conditions, except that the expansion temperature during the heating-pressure increasing step and the holding step is set 1°C lower, and the "heat of fusion of the highest-temperature melting peak" of the expanded beads to be evaluated. Expanded beads having a temperature dependence of 3.0 (J/g)/°C or less can be said to be expanded beads "which have a desired heat of fusion on the high-temperature side and can be stably produced," or in other words, expanded beads with excellent stable productivity.

From the viewpoint of providing expanded beads of more stable quality, the temperature dependence of the expanded beads is 3.0 (J/g)/°C or less, preferably 2.8 (J/g)/°C or less, more preferably 2.5 (J/g)/°C or less, even more preferably 2.2 (J/g)/°C or less, and even more preferably 1.8 (J/g)/°C or less.

Expanded beads with excellent stable productivity, whose temperature dependence is within the above range, can be produced stably with the desired high-temperature heat of fusion even when produced in large-scale production equipment where precise temperature control is difficult. In other words, expanded beads with the desired high-temperature heat of fusion can be provided more efficiently. Therefore, expanded beads with excellent stable productivity can also be said to be expanded beads with excellent production efficiency.

(Apparent density of expanded particles)
The apparent density of the expanded beads is not particularly limited, but is preferably 20 g/L to 150 g/L, more preferably 23 g/L to 140 g/L, and even more preferably 25 g/L to 130 g/L. When the apparent density of the expanded beads is 20 g/L to 150 g/L, it is possible to provide a foamed molded article that is excellent in balance between light weight and physical properties (for example, strength and heat insulation).

In this specification, the method for measuring the apparent density of expanded beads is as follows (1) to (3): (1) placing expanded beads with a mass Wd (g) on a wire netting and immersing the netting in ethanol contained in a measuring cylinder; (2) measuring the volume Vd (L) of the expanded beads based on the rise in the liquid level in the measuring cylinder; (3) calculating the apparent density of the expanded beads based on the following formula:
Apparent density of expanded beads (g/L) = Wd (g)/Vd (L).

(Gel fraction of expanded beads)
In this specification, the gel fraction of expanded beads is an index showing the degree of crosslinking (degree of crosslinking) of the P3HA-based resin in the expanded beads. Expanded beads with a gel fraction of 0.1% or more are said to have a crosslinked structure. Furthermore, the higher the gel fraction of expanded beads, the higher the degree of crosslinking of the expanded beads, in other words, the more crosslinked structures they have.

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, the molding temperature range of the expanded beads that can provide high-quality expanded molded articles is broadened, resulting in improved productivity. When the gel fraction is (b) 80% by weight or less, the advantage is that expanded beads with a sufficiently low apparent density can be easily obtained with a single expansion.

The method for crosslinking the expanded beads (introducing a crosslinked structure) is not particularly limited, but an example is a method in which a crosslinking agent is added during the production of the expanded beads. The gel fraction of the expanded beads can be controlled by the type and/or amount of crosslinking agent used.

In this specification, the method for measuring the gel fraction of expanded beads is as follows (1) to (5): (1) 0.5 g of expanded beads and 50 ml of chloroform are placed in a 100 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 of the dried product, Wgw (g), is measured; (5) the gel fraction is calculated using the following formula:
Gel fraction (wt%)={Wgw/0.5}×100.

3. Method for producing P3HA-based expanded beads
The method for producing the expanded beads is not particularly limited, but a preferred method is one that includes, in order, a resin particle preparation step of preparing resin particles containing a resin composition, which resin particles have a DSC curve obtained by differential scanning calorimetry, a difference between the melting peak temperature and the melting end temperature of 8°C to 20°C, and a heat of fusion above the melting peak temperature of 5 J/g to 15 J/g, and an expansion step of expanding the resin particles. Hereinafter, the method for producing the expanded beads will be described using an example of such a production method that includes, in order, a resin particle preparation step and an expansion step. It should be noted that the method for producing the expanded beads is not limited to the following production method.

(Resin particle preparation process)
The resin particle preparation step is a step of preparing resin particles that contain a resin composition and have a DSC curve obtained by differential scanning calorimetry, in which the difference between the melting peak temperature and the melting end temperature is 8°C to 20°C, and the heat of fusion above the melting peak temperature is 5 J/g to 15 J/g. 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 granulating (molding) a resin composition containing a P3HA-based resin 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.

The resin particle preparation step includes:
(a) a melt-kneading step of melt-kneading a resin composition containing a P3HA-based resin and, if necessary, other resins and additives;
(b) a granulation step of granulating the melt-kneaded resin composition into a shape that is easily usable for foaming.

The descriptions in Section 2. Poly(3-hydroxyalkanoate)-Based Expanded Particles can be used as appropriate for the types and properties of the P3HA-based resin melt-kneaded in the resin particle preparation process and the resin composition granulated.

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

The form of the granulation process is not particularly limited, as long as it allows the melt-kneaded resin composition to be molded into the desired shape. By using a melt-kneading device equipped with a die and a cutting device as the melt-kneading device, the melt-kneaded resin composition can be easily molded into the desired shape in the granulation process. Specifically, the melt-kneaded resin composition is discharged from the die nozzle of the melt-kneading device, and then cut with the cutting device simultaneously with or after discharge, thereby molding into the desired shape. The shape of the resulting resin particles is not particularly limited, but cylindrical, elliptical, spherical, cubic, rectangular, etc. are preferred because they are easy to use for foaming.

(Foaming process)
The form of the expansion step in the method for producing expanded beads of the present invention 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 (e.g., distilled water, deionized water, etc.), a crosslinking agent (e.g., an organic peroxide such as t-butylperoxy-2-ethylhexyl carbonate), a foaming agent (e.g., an inorganic gas such as carbon dioxide), and, if necessary, a dispersant (e.g., an inorganic substance such as tricalcium phosphate and kaolin), and/or a dispersing aid (e.g., an anionic surfactant such as sodium alkanesulfonate), etc., 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).

In the dispersion process, when the resin particles are impregnated and reacted with the crosslinking agent, it is preferable to reduce the oxygen concentration in the container and the amount of dissolved oxygen in the dispersion in order to increase the crosslinking efficiency of the P3HA-based resin. 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.

(Temperature-pressure increase step and holding step)
The temperature-pressure increasing step is preferably carried out after the dispersing step, and the holding step is preferably carried out after the temperature-pressure increasing step. In this specification, (a) the constant temperature in the temperature-pressure increasing step and the holding step may be referred to as the foaming temperature, and (b) the constant pressure in the foaming step may be referred to as the foaming pressure.

The foaming temperature cannot be generally defined, as it varies depending on factors such as the type of P3HA resin, the type of blowing agent, the degree of plasticization of the P3HA resin, and the desired apparent density of the expanded beads. However, it is preferable to set the foaming temperature lower than the peak melting temperature (Tmp) of the resin beads before foaming. For example, the foaming temperature is preferably (Tmp - 25)°C to (Tmp - 10)°C, more preferably (Tmp - 20)°C to (Tmp - 15)°C, and even more preferably (Tmp - 19)°C to (Tmp - 16)°C. Foaming temperatures within the above ranges can more stably provide expanded beads with the desired high-temperature heat of fusion. Furthermore, foaming temperatures of (Tmp - 25)°C or higher tend to produce expanded beads with an appropriate density. On the other hand, foaming temperatures of (Tmp - 10)°C or lower tend to reduce hydrolysis of the resin beads in the container.

The expansion pressure is preferably 1.0 MPa (gauge pressure) to 10.0 MPa (gauge pressure), more preferably 2.0 MPa (gauge pressure) to 5.0 MPa (gauge pressure), and even more preferably 2.5 MPa (gauge pressure) to 4.0 MPa (gauge pressure). If the expansion pressure is 1.0 MPa (gauge pressure) or higher, expanded beads with a suitable density can be obtained.

In the holding step, the time (holding time) for which the dispersion in the container is held at near the foaming temperature and foaming pressure is not particularly limited, but a holding time of 5 to 120 minutes is preferred, 10 to 120 minutes is more preferred, 15 to 90 minutes is even more preferred, and 15 to 70 minutes is particularly preferred. When the holding time is within the above range, expanded beads with the desired high-temperature heat of fusion can be more stably provided. Furthermore, when the holding time is 5 minutes or longer, unreacted crosslinking agent tends to be less likely to remain. On the other hand, when the holding time is 120 minutes or less, excessive hydrolysis of the P3HA contained in the resin particles tends to be less likely to occur.

(Release process)
The releasing step is preferably carried out after the temperature-pressure increasing step or after the holding step. The releasing step allows the resin particles to expand, resulting in expanded particles.

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

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

4. P3HA foam molded article
In one embodiment of the present invention, a foamed molded article is provided by molding the foamed beads. The foamed molded article can be said to be a foamed molded article containing the foamed beads, or can be said to be a foamed molded article containing the resin composition.

(Density of foamed molded product)
The density (apparent density) of the foamed molded article is not particularly limited, but is preferably 20 g/L to 300 g/L, more preferably 23 g/L to 250 g/L, and even more preferably 25 g/L to 200 g/L. When the density of the foamed molded article is (a) 20 g/L or more, the foamed molded article has the advantage of being excellent in cushioning properties and/or mechanical strength, and when the density is (b) 300 g/L or less, the foamed molded article has the advantage of being excellent in light weight.

In this specification, the methods for measuring the density (apparent density) of a foam molded article are as follows (1) to (3): (1) measure the length (mm) in the vertical direction, the length (mm) in the horizontal direction, and the length (mm) in the thickness direction (driving direction of the moving mold) of the obtained foam molded article with vernier calipers, and calculate the volume V (L) of the foam molded article; (2) measure the weight W (g) of the foam molded article (foam molded article with volume V); (3) calculate the density of the foam molded article based on the following formula:
Density of foamed molded article (g/L) = W/V.

<Method for producing a poly(3-hydroxyalkanoate) foam molded article>
The method for producing the foamed molded article (i.e., the method for molding the foamed beads) is not particularly limited, and any known method can be used. For example, the following in-mold foam molding methods (A) to (D) can be mentioned, but are not particularly limited:
(A) A method in which the expanded beads are pressurized with an inorganic gas in a container to impregnate the expanded beads with the inorganic gas, and then the expanded beads are filled into a mold and heated with steam;
(B) A method in which the expanded beads are filled into a mold, compressed to reduce the volume of the mold by 10% to 75%, and then heated with steam;
(C) A method in which the expanded beads are compressed by gas pressure, filled into a mold, and heated with steam, utilizing the recovery force of the expanded beads;
(D) A method in which the present expanded beads are filled into a mold without any particular pretreatment and heated with steam.

The present invention will be explained in detail below using examples, but the technical scope of the present invention is not limited to these examples.

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

(Poly(3-hydroxyalkanoate))
P3HA-1: P3HB3HH (the monomer ratio in P3HB3HH was 3HB/3HH=95.5/4.5 (mol %/mol %))
P3HA-2: P3HB3HH (the monomer ratio in P3HB3HH was 3HB/3HH=93.0/7.0 (mol %/mol %))
P3HA-3: P3HB3HH (the monomer ratio in P3HB3HH was 3HB/3HH=95.0/5.0 (mol %/mol %))
P3HA-4: Homopolymer of P3HB. These P3HAs were produced by the method described in International Publication No. 2018/070492.

(Foam adjuster)
Talc (Talc Powder PK-S manufactured by Hayashi Kasei Co., Ltd.)
(Crystal nucleating agent)
Pentaerythritol (Neuraizer P, manufactured by Mitsubishi Chemical Corporation)
(lubricant)
Lubricant-1: Behenic acid amide (Crodamide (registered trademark) BR manufactured by CRODA)
Lubricant-2: Erucamide (Crodamide (registered trademark) ER manufactured by CRODA)
(Dispersant)
Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.)
(Dispersing aid)
Sodium alkanesulfonate (Latemul (registered trademark) PS, manufactured by Kao Corporation)
(Crosslinking agent)
t-Butylperoxy-2-ethylhexyl carbonate (Perbutyl (registered trademark) E, manufactured by NOF Corporation, purity (content): 97%)
(Blowing agent)
Carbon dioxide (manufactured by Air Water Inc.)
[Measurement method]
The evaluation methods used in the examples and comparative examples are described below.

(Difference between the peak melting temperature and the end melting temperature of resin particles)
The method for measuring the difference between the melting peak temperature and the melting end temperature of the resin particles was as follows (1) to (3): (1) Approximately 5 mg of resin particles were weighed out; (2) Using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Science Corporation), the temperature of the resin particles was raised from 10°C to 190°C at a heating rate of 10°C/min. In the DSC curve obtained, the temperature of the melting peak on the highest temperature side was taken as the melting peak temperature (Tmp); (3) Furthermore, the temperature at the end of melting was taken as the melting end temperature (Tme), and the difference between the measured Tmp and Tme (Tme - Tmp) was taken as the difference between the melting peak temperature and the melting end temperature of the resin particles (ΔTrp).

(Amount of heat of fusion above the peak melting temperature of resin particles)
The method for measuring the heat of fusion above the melting peak temperature of the resin particles was as follows (1) to (5): (1) Approximately 5 mg of resin particles were weighed out; (2) Using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Science Corporation), the temperature of the resin particles was raised from 10°C to 190°C at a heating rate of 10°C/min to melt the resin particles; (3) In the DSC curve obtained in the process (2), a baseline was created by connecting the point representing the temperature at the start of melting and the point representing the melting end temperature (Tme) with a straight line; (4) A line passing through the melting peak on the highest temperature side was drawn perpendicular to the X-axis (temperature axis); (5) The heat of fusion calculated from the higher temperature region of the region surrounded by the created baseline, the line passing through the melting peak temperature, and the DSC curve was defined as the heat of fusion above the melting peak temperature of the resin particles (MErp).

(MFR of resin particles)
The MFR of the resin particles was determined by measuring the MFR at a load of 5 kg using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K 7210. The measurement temperature was set to a value obtained by measuring at a temperature between 1°C and 10°C above the melting end temperature read from the DSC curve obtained by the "difference between the melting peak temperature and the melting end temperature of the resin particles."

(Heat of fusion above the peak melting temperature of the expanded beads)
The method for measuring the heat of fusion above the melting peak temperature of the expanded beads was as follows (1) to (5): (1) Approximately 5 mg of expanded beads were weighed; (2) Using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Science Corporation), the temperature of the expanded beads was raised from 10°C to 190°C at a heating rate of 10°C/min to melt the expanded beads; (3) In the DSC curve obtained in the process (2), a line representing the temperature at the start of melting and a line representing the temperature at the end of melting were connected to form a baseline; (4) A line passing through the maximum point between the highest melting peak and the melting peak next to the highest melting peak (a line passing through the maximum point) was drawn perpendicular to the X-axis (temperature axis); (5) The heat of fusion calculated from the highest temperature region among the region surrounded by the prepared baseline, the line passing through the maximum point, and the DSC curve was determined as the heat of fusion above the melting peak temperature of the expanded beads.

(Temperature Dependence of Expanded Beads)
The temperature dependence of expanded beads was measured as follows (1) and (2): (1) resin beads used as the raw material for the expanded beads to be measured were expanded under the same conditions as those for the expanded beads to be evaluated, except that the expansion temperature in the temperature-pressure increase step and the holding step was set to a temperature 1°C lower, to obtain comparative expanded beads; (2) the difference (amount of change per 1°C) between the "heat of fusion of the highest temperature melting peak" of the obtained comparative expanded beads and the "heat of fusion of the highest temperature melting peak" of the expanded beads to be evaluated was taken as the temperature dependence of the expanded beads. The "heat of fusion of the highest temperature melting peak" of the expanded beads to be evaluated and the comparative expanded beads was measured as described in the section (heat of fusion above the melting peak temperature of the expanded beads).

(Stable productivity of expanded beads)
The stable productivity of the expanded beads was evaluated according to the following criteria:
◯ (Good): The temperature dependency of the expanded beads is 3.0 (J/g)/°C or less. × (Poor): The temperature dependency of the expanded beads is more than 3.0 (J/g)/°C.

Expanded beads rated as good (good) for stable productivity can produce expanded beads of stable quality (having a heat of fusion above the desired peak melting temperature) even when the expansion temperature changes. On the other hand, expanded beads rated poor (poor) for stable productivity show a large change in the heat of fusion above the peak melting temperature when the expansion temperature changes, making it difficult to produce expanded beads of stable quality.

(Apparent density of expanded particles)
The apparent density of the expanded beads was measured by the following methods (1) to (3): (1) Expanded beads with a mass Wd (g) were placed on a wire net and immersed in ethanol contained in a measuring cylinder; (2) The volume Vd (L) of the expanded beads was measured based on the rise in the liquid level in the measuring cylinder; (3) The apparent density of the expanded beads was calculated based on the following formula:
Apparent density of expanded beads (g/L) = Wd (g)/Vd (L).

(Gel fraction of expanded beads)
The gel fraction of the expanded beads was measured by the following methods (1) to (5): (1) 0.5 g of expanded beads and 50 ml of chloroform were placed in a 100 ml flask; (2) the mixture in the flask was heated under reflux at 62°C under atmospheric pressure for 8 hours; (3) the resulting heat-treated product was filtered using a suction filtration device equipped with a 100-mesh wire mesh; (4) the filtered product on the wire mesh was dried in an oven at 80°C under vacuum for 8 hours, and the weight of the dried product, Wgw (g), was measured; (5) the gel fraction was calculated by the following formula:
Gel fraction (wt%)={Wgw/0.5}×100.

(Density of foamed molded product)
The density of the foam molded article (foam molded article density) was measured by the following methods (1) to (3): (1) The lengths (mm) of the obtained foam molded article in the longitudinal direction (mm), transverse direction (mm), and thickness direction (driving direction of the moving mold) were measured with digital calipers (ABS Digimatic Caliper CD-45C manufactured by Mitutoyo Corporation), and the volume V (L) of the foam molded article was calculated; (2) The weight W (g) of the foam molded article was measured; (3) The density of the foam molded article was calculated based on the following formula:
Density of foamed molded article (g/L) = W/V.

Example 1
(Resin particle preparation process)
A resin composition was obtained by weighing and dry-blending 100 parts by weight of a mixture of P3HA-1 and P3HA-2 (80% by weight of P3HA-1, 20% by weight of P3HA-2) as a P3HA-based resin, 0.1 parts by weight of a cell regulator, 1.0 parts by weight of a crystal nucleating agent, 0.10 parts by weight of Lubricant-1, and 0.10 parts by weight of Lubricant-2. The resulting resin composition was melt-kneaded using a twin-screw extruder (TEM-26SX manufactured by Toshiba Machine Co., Ltd.) at a cylinder setting temperature of 140°C to 165°C to obtain a melt-kneaded product. The resulting melt-kneaded product was water-cooled to 43°C and then cut to obtain resin particles weighing 1.6 mg per particle. The resulting resin particles were measured for peak melting temperature, end melting temperature, difference between peak melting temperature and end melting temperature, heat of fusion above the peak melting temperature, and MFR. The results are shown in Table 1.

(Foaming process)
100 parts by weight of the resin particles obtained in the resin particle preparation step, 200 parts by weight of pure water, 1.0 part by weight of dispersant, 0.1 part by weight of dispersing aid, and 2 parts by weight of crosslinker were placed in a pressure-resistant vessel under stirring, and then thoroughly aerated with carbon dioxide gas to remove oxygen from the pressure-resistant vessel. Next, carbon dioxide was introduced into the pressure-resistant vessel as a foaming agent. The contents of the pressure-resistant vessel were then heated to a foaming temperature of −25°C to −10°C (129.5°C in Example 1), which was the melting peak temperature of the resin composition. Further, carbon dioxide was introduced into the pressure-resistant vessel to raise the pressure inside the pressure-resistant vessel to a foaming pressure of 3.3 MPa (gauge pressure), and the pressure was maintained at or near the foaming temperature for 60 minutes. The valve at the bottom of the pressure-resistant vessel was then opened, and the contents of the pressure-resistant vessel were released to atmospheric pressure through a 3.6 mm diameter orifice, yielding expanded beads. The dispersant adhering to the surface of the expanded beads was washed away, and the beads were then dried at 90°C. The heat of fusion of the highest temperature melting peak, the number of melting peaks, the apparent density, and the gel fraction of the resulting expanded beads (expanded beads after drying) were measured. The results are shown in Table 1.

Next, to confirm the temperature dependence of the expanded beads, expanded beads (comparative expanded beads) were obtained in the same manner as above, except that the expansion temperature was changed to a temperature 1°C lower (128.5°C in Example 1), and the heat of fusion of the highest temperature melting peak of the obtained comparative expanded beads was measured. The temperature dependence of the expanded beads was calculated based on the obtained heat of fusion of the highest temperature melting peak and the heat of fusion of the highest temperature melting peak of the comparative expanded beads. Furthermore, the stable productivity of the expanded beads was evaluated based on the calculated temperature dependence of the expanded beads. The results are shown in Table 1.

(Production of foamed molded article)
The expanded beads obtained in the expansion step (expanded beads with an expansion temperature of 129.5°C) were placed in a pressure-resistant container heated to 80°C and pressurized with air to adjust the internal pressure of the expanded beads to 0.15 MPa (absolute pressure). The expanded beads were filled into a mold of a 370 mm long x 320 mm wide x 60 mm thick molding machine (EP-900L-M5 manufactured by DAISEN Co., Ltd.). Next, a foamed molded article was obtained by heating with heated steam at a pressure of 0.15 MPa (gauge pressure), and the obtained foamed molded article was dried at 75°C. The density of the obtained foamed molded article is shown in Table 1. Furthermore, when the surface of the obtained foamed molded article was visually inspected, the foamed molded article had almost no gaps between the foamed beads on the surface and was free of sink marks.

[Examples 2 and 3, Comparative Examples 1 and 2]
Resin particles and expanded particles were produced in the same manner as in Example 1, except that the type and amount of P3HA resin were changed as shown in Table 1, and the physical properties were measured and evaluated in the same manner as in Example 1. The results are shown in Table 1. When the surfaces of the expanded molded articles obtained in Examples 2 and 3 were visually inspected, it was found that there were almost no gaps between the expanded beads on the surface and that these expanded molded articles were all expanded molded articles without sink marks.

〔summary〕
From Table 1, the following can be clearly seen:
(1) The expanded beads of Examples 1 to 3, which are obtained by expanding resin beads having a difference between the peak melting temperature and the end melting temperature in the range of 8°C to 20°C and a heat of fusion above the peak melting temperature in the range of 5 J/g to 15 J/g, all have a temperature dependency of 3.0 (J/g)/°C or less, and are expanded beads with excellent stable productivity, i.e., they have a desired heat of fusion on the high-temperature side and can be stably produced. Furthermore, it is also found that the expanded molded articles obtained by molding the expanded beads of Examples 1 to 3 have almost no gaps between the expanded beads on the surface, are free of sink marks, and are expanded molded articles with excellent surface properties and shrinkage suppression.

(2) A comparison of Examples 1 to 3 with Comparative Example 1 reveals that expanded beads obtained by expanding resin beads whose difference between the peak melting temperature and the end melting temperature is outside the range of 8°C to 20°C have a temperature dependency of more than 3.0 (J/g)/°C, making it impossible to stably produce expanded beads with the desired high-temperature heat of fusion.

(3) A comparison of Examples 1 to 3 with Comparative Example 2 reveals that expanded beads obtained by expanding resin beads whose difference between the peak melting temperature and the end melting temperature is outside the range of 8°C to 20°C have a temperature dependency of more than 3.0 (J/g)/°C, making it impossible to stably produce expanded beads with the desired high-temperature heat of fusion.

According to one embodiment of the present invention, expanded beads can be provided that have a desired heat of fusion at a high temperature and can be produced stably. Molded foams obtained by molding these expanded beads can be suitably used in a variety of applications, including packaging cushioning (e.g., cushioning for packaging home appliances such as refrigerators, freezers, air conditioner bodies and their outdoor units, washing machines, air purifiers, humidifiers, rice cookers, microwave ovens, ovens, toasters, fans, and storage battery units; and cushioning for packaging automotive items such as transmissions, roofs, hoods, doors, batteries, and engines), automotive components (e.g., bumper cores, headrests, luggage boxes, toolboxes, floor spacers, seat cores, child car seat cores, sun visor cores, and knee pads), thermal insulation (e.g., containers for constant-temperature storage and constant-temperature transport), casting models, agricultural product boxes, fish boxes, building materials, and civil engineering materials.

Claims (4)

The expanded poly(3-hydroxyalkanoate) particles are obtained by expanding poly(3-hydroxyalkanoate) resin particles containing a poly(3-hydroxyalkanoate) resin composition,
the poly(3-hydroxyalkanoate) resin particles have a DSC curve obtained by differential scanning calorimetry, in which the difference between the melting peak temperature and the melting end temperature is 8°C to 20°C, and the heat of fusion at temperatures equal to or higher than the melting peak temperature is 5 J/g to 15 J/g;
the poly(3-hydroxyalkanoate)-based resin composition contains P3HB3HH(A) and P3HB3HH(B);
Each of the P3HB3HH(A) and the P3HB3HH(B) contains a 3-hydroxybutyrate unit (3HB unit) and a 3-hydroxyhexanoate unit (3HH unit),
a ratio of the 3HB units to the 3HH units (the 3HB units/the 3HH units) in 100 mol% of all repeating units in the P3HB3HH(A) is 98.0/2.0 (mol%/mol%) to 94.0/6.0 (mol%/mol%);
a ratio of the 3HB units to the 3HH units (the 3HB units/the 3HH units) in 100 mol% of all repeating units in the P3HB3HH(B) is 93.9/6.1 (mol%/mol%) to 90.0/10.0 (mol%/mol%),
The weight ratio of the P3HB3HH(A) to the P3HB3HH(B) (weight of the P3HB3HH(A)/weight of the P3HB3HH(B)) is 90/10 (wt %) to 10/90 (wt %) . The poly(3-hydroxyalkanoate)-based expanded particles according to claim 1, wherein the poly(3-hydroxyalkanoate)-based expanded particles have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry. 3. The expanded poly(3-hydroxyalkanoate) beads according to claim 2 , wherein the heat of fusion of the highest temperature melting peak among at least two melting peaks observed in the DSC curve obtained by the differential scanning calorimetry is 0.1 J/g to 20.0 J/g. A poly(3-hydroxyalkanoate)-based expanded molded article obtained by molding the poly(3-hydroxyalkanoate)-based expanded beads according to any one of claims 1 to 3 .