JP7646352B2 - Poly(3-hydroxyalkanoate)-based expanded particles and poly(3-hydroxyalkanoate)-based expanded molded articles - Google Patents

Description

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

A large amount of petroleum-derived plastics are discarded every year, and the shortage of landfill sites and environmental pollution caused by this large amount of waste are being raised as 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 environment, such as the sea and soil, and (b) in landfill sites and compost, have attracted attention. Development of biodegradable plastics is being promoted with the aim of wide-ranging applications to (a) agricultural, forestry and fishery materials used in the environment, and (b) food containers, packaging materials, sanitary products, garbage bags, etc., which are difficult to recover and reuse after use. Furthermore, foams made of biodegradable plastics are expected to be used in packaging cushioning materials, agricultural product boxes, fish boxes, automotive parts, building materials, civil engineering materials, etc.

Among the above biodegradable plastics, poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as "P3HA") is attracting attention as a plastic derived from plant raw materials due to its excellent biodegradability and carbon neutrality.

The use of the above-mentioned biodegradable plastics in molded articles is being considered. For example, Patent Document 1 discloses expanded beads obtained using biodegradable P3HA, and a technique for obtaining a molded foam by in-mold foaming of the expanded beads. Patent Document 2 discloses a technique for obtaining a molded article by injection molding that contains P3HA and also contains pentaerythritol as a crystal nucleating agent.

International Publication No. 2019/146555 International Publication No. 2014/020838

However, the above-mentioned conventional techniques leave room for improvement in terms of the molding pressure when molding P3HA-based expanded beads and the internal fusion properties of P3HA-based expanded molded bodies.

In view of the above circumstances, an object of one embodiment of the present invention is to provide P3HA-based foamed particles and a P3HA-based foamed molded product that can provide a P3HA-based foamed molded product with excellent internal fusion properties at low molding pressure.

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

That is, one embodiment of the present invention includes the following configuration.
[1] A poly(3-hydroxyalkanoate)-based expanded particle, comprising poly(3-hydroxyalkanoate) and pentaerythritol, the content of the pentaerythritol being 0.01% by weight to 4.50% by weight relative to 100% by weight of the poly(3-hydroxyalkanoate)-based expanded particle.
[2] A poly(3-hydroxyalkanoate)-based expanded bead having a DSC ratio of 0.5% to 40.0%, wherein the DSC ratio is calculated by the following formula (1):
DSC ratio (%) = (high temperature side heat of fusion/total heat of fusion) x 100 (1),
In the formula (1), the high-temperature side heat of fusion and the total heat of fusion are heat quantities obtained from a DSC curve of the poly(3-hydroxyalkanoate)-based expanded beads according to [1].
[3] The expanded poly(3-hydroxyalkanoate) beads according to [1] or [2], having a gel fraction of 50% by weight to 80% by weight.
[4] The poly(3-hydroxyalkanoate)-based expanded beads according to any one of [1] to [3], further comprising 0.01% by weight to 1.50% by weight of a fatty acid amide relative to 100% by weight of the poly(3-hydroxyalkanoate)-based expanded beads.
[5] A poly(3-hydroxyalkanoate)-based foamed molded article obtained by molding the poly(3-hydroxyalkanoate)-based foamed beads according to any one of [1] to [4].
[6] A method for producing expanded poly(3-hydroxyalkanoate)-based particles, comprising a foaming step of foaming poly(3-hydroxyalkanoate)-based resin particles containing 100 parts by weight of poly(3-hydroxyalkanoate) and 0.01 to 20.00 parts by weight of pentaerythritol, the foaming step including a dispersing step of dispersing the poly(3-hydroxyalkanoate)-based resin particles in an aqueous dispersion medium.
[7] A method for producing a poly(3-hydroxyalkanoate)-based foamed molded article, comprising: a filling step of filling a molding space formed by at least two molds provided in a mold with the poly(3-hydroxyalkanoate)-based foamed beads according to any one of [1] to [4]; and a fusion step of heating the filled poly(3-hydroxyalkanoate)-based foamed beads to fuse the poly(3-hydroxyalkanoate)-based foamed beads together.

According to one embodiment of the present invention, it is possible to provide P3HA-based foamed particles and P3HA-based foamed molded products that can provide P3HA-based foamed molded products with excellent internal fusion properties at low molding pressures.

FIG. 2 is a diagram showing a DSC curve of P3HA-based resin particles and the melting point and the like measured therefrom. FIG. 2 is a diagram showing a DSC curve of P3HA-based expanded beads and the heat of fusion on the high temperature side measured therefrom. FIG. 3 is a perspective view of a P3HA-based foam molded article 100 according to one embodiment of the present invention, viewed from one direction. FIG. 4 is a cross-sectional view taken along line AA of FIG.

One embodiment of the present invention will be described below, but the present invention is not limited to this. The present invention is not limited to each of the configurations described below, and various modifications are possible within the scope of the claims. In addition, 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. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range intends "A or more (including A and greater than A) and B or less (including B and smaller than B)."

1. Technical Concept of the Present Invention
Pentaerythritol is known to act as a crystal nucleating agent for P3HA. Pentaerythritol can improve the dimensional stability of molded bodies due to its crystallization effect, and is therefore used in P3HA-based resin compositions for injection molding, as described in Patent Document 2. On the other hand, pentaerythritol may inhibit internal fusion between P3HA-based expanded particles due to its crystallization effect during molding of the P3HA-based expanded particles. Therefore, pentaerythritol has not been used in actual P3HA-based expanded molded products.

P3HA foam molded products with poor internal fusion have low impact resistance and are prone to accidental breakage during production, resulting in poor productivity. In particular, when producing P3HA foam molded products with parts of different dimensions, the low impact resistance caused by poor internal fusion can be a major problem. As a result, P3HA foam molded products with poor internal fusion also have the problem of being prone to breakage during distribution on the market.

Increasing the molding pressure when molding P3HA-based foamed particles is known as a method for improving the internal fusion properties of P3HA-based foamed molded articles. However, increasing the molding pressure also increases the economic burden. Therefore, there has been a demand for P3HA-based foamed particles that can provide P3HA-based foamed molded articles with excellent internal fusion properties at low molding pressures.

In light of the above circumstances, the present inventors have conducted extensive research with the aim of providing P3HA-based expanded particles that can produce P3HA-based expanded molded articles with excellent internal fusion properties at low molding pressures.

As a result of intensive research, the inventors independently discovered the following, which led to the completion of the present invention: P3HA-based expanded particles containing a specific amount of pentaerythritol can surprisingly provide a P3HA-based expanded molded article with excellent internal fusion properties at low molding pressures.

2. Poly(3-hydroxyalkanoate)-based expanded particles
The poly(3-hydroxyalkanoate)-based expanded beads according to one embodiment of the present invention are poly(3-hydroxyalkanoate)-based expanded beads, which contain poly(3-hydroxyalkanoate) and pentaerythritol, and the content of the pentaerythritol is 0.01% by weight to 4.50% by weight based on 100% by weight of the poly(3-hydroxyalkanoate)-based expanded beads.

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

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.

The foamed beads have the above-mentioned configuration, and therefore have the advantage of being able to provide foamed molded articles with excellent internal fusion at low molding pressures. The foamed molded articles can be produced by molding the foamed beads by known methods.

The expanded particles are obtained by expanding poly(3-hydroxyalkanoate)-based resin particles made of a poly(3-hydroxyalkanoate)-based resin composition. 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."

(Poly(3-hydroxyalkanoate))
P3HA according to one embodiment of the present invention is a polymer having a 3-hydroxyalkanoate unit as an essential constituent 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-CH ₂ -CO-O-]...(2).

In general formula (2), 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. n is preferably 1 to 10, and more preferably 1 to 8.

P3HA produced from microorganisms is particularly preferred as P3HA. P3HA produced from microorganisms is poly[(R)-3HA] in which all 3HA units are (R)-3HA.

P3HA preferably contains 3HA units (particularly the 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, out of 100 mol% of all repeating units of P3HA. Furthermore, the repeating units (monomer units) may be 3HA units only, or may contain, in addition to 3HA units, repeating 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 according to one embodiment of the present invention contains 3-hydroxybutyrate units. In this specification, "3-hydroxybutyrate" may also be referred to as "3HB."

P3HA preferably contains 80 mol% or more, and more preferably 85 mol% or more, of 100 mol% of all repeating units of P3HA as 3HB units (monomer units). In particular, P3HA is preferably a polymer that contains 3HB units and in which all 3HB is (R)-3HB (a polymer produced by a microorganism).

When P3HA contains two or more types of repeating units, the monomer from which the repeating units other than the repeating unit with the highest 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."

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

Specific examples of P3HA 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), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter, sometimes referred to as "P3HB3HH"), poly Examples of the 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), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter, sometimes referred to as "P3HB4HB"). In particular, from the viewpoint of processability and physical properties of foamed molded products, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred. In one embodiment of the present invention, the above-mentioned P3HA may be used alone or in combination of two or more types.

It is preferable that P3HA has a 3HB unit as an essential repeating unit (structural unit) and also has a comonomer unit. That is, it is preferable that P3HA is a copolymer having a 3HB unit and a comonomer unit. The case where P3HA has a 3HB unit and a comonomer unit will be described. In this case, the ratio of the 3HB unit and the comonomer unit (3HB unit/comonomer unit) 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%). If the ratio of the comonomer unit to 100 mol% of all repeating units of P3HA is 1 mol% or more, the melt-kneadable temperature range of P3HA and the thermal decomposition temperature range are sufficiently separated, so that the obtained expanded beads have excellent processability. On the other hand, if the ratio of the comonomer units to the total repeating units of P3HA (100 mol%) is 20 mol% or less, the P3HA composition crystallizes quickly during melt kneading, 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.

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 International Publication WO 2013/147139.

The melting point of P3HA is not particularly limited, but is preferably 110.0°C to 165.0°C, and more preferably 120.0°C to 155.0°C. If the melting point of P3HA is 110.0°C or higher, there is no risk of dimensional change upon heating of the resulting foamed molded article, while if the melting point of P3HA is 165.0°C or lower, there is no risk of hydrolysis occurring during the foaming process.

The melting point of P3HA was measured by differential scanning calorimetry (hereinafter referred to as "DSC method"). The specific procedure is as follows: (1) 5 mg to 6 mg of P3HA is weighed out; (2) The temperature of P3HA is increased from 10.0°C to 190.0°C at a heating rate of 10.0°C/min to melt the P3HA; (3) The temperature of the highest melting peak in the DSC curve of P3HA obtained in the above process (2) can be determined as the melting point of P3HA.

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

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

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

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.

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

The expanded particles 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, or (b) aliphatic aromatic polyesters. One of these other resin components may be used alone together with P3HA, or two or more may be used in combination.

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

(Pentaerythritol)
The present expanded beads contain pentaerythritol. The content of pentaerythritol in the present expanded beads is 0.01% by weight to 4.50% by weight, preferably 0.05% by weight to 4.00% by weight, more preferably 0.10% by weight to 2.50% by weight, and even more preferably 0.15% by weight to 1.50% by weight, based on 100% by weight of the expanded beads. When the content of pentaerythritol in the expanded beads is 0.01% by weight to 4.50% by weight, based on 100% by weight of the expanded beads, a foamed molded product having excellent internal fusion properties can be provided at a low molding pressure. In particular, when the content of pentaerythritol in the expanded beads is 0.01% by weight or more based on 100% by weight of the expanded beads, pentaerythritol can exert the desired effect. When the content of pentaerythritol in the expanded beads is 4.50% by weight or less relative to 100% by weight of the expanded beads, there is no risk of pentaerythritol seeping out (bleeding) in large amounts onto the surface of the expanded beads. Therefore, the expanded beads obtained are not sticky and have good handleability. As a result, when the expanded beads are used to form a foamed molded article in a mold, the expanded beads have the advantage of being well filled into the mold. When the content of pentaerythritol in the expanded beads is 4.50% by weight or less relative to 100% by weight of the expanded beads, when the expanded beads are used to form a foamed molded article, the fusion between the expanded beads during molding is also good, and a foamed molded article with excellent internal fusion can be obtained.

Pentaerythritol is a compound represented by the following general formula (3):

Pentaerythritol is a type of polyhydric alcohol and is a white crystalline organic compound with a melting point of 260.5°C. Pentaerythritol is classified as a sugar alcohol, but is not naturally derived. Pentaerythritol can be synthesized by condensing acetaldehyde and formaldehyde in a basic environment.

Commercially available pentaerythritol may be used in the present invention. Commercially available pentaerythritol products include, but are not limited to, those manufactured by Perstorp, Mitsubishi Chemical Corporation, Fujifilm Wako Pure Chemical Industries, Ltd., Sigma-Aldrich, Tokyo Chemical Industry Co., Ltd., Merck & Co., Ltd., Koei Chemical Industry Co., Ltd. (trade name: Pentalyt), and Toyo Chemicals Co., Ltd.

Some commercially available pentaerythritol products contain impurities such as oligomers, such as dipentaerythritol and tripentaerythritol, which are produced by dehydration condensation of pentaerythritol. These oligomers do not have the effect of crystallizing P3HA, but they do not inhibit the function of pentaerythritol. Therefore, the pentaerythritol used in one embodiment of the present invention may contain the above-mentioned oligomers.

(Fatty acid amide)
The present expanded beads preferably contain a fatty acid amide. When the present expanded beads contain a fatty acid amide, the expanded beads can provide an expanded molded article having excellent internal fusion properties at a low molding pressure without inhibiting the effect of adding pentaerythritol.

Examples of fatty acid amides include behenic acid amide, erucic acid amide, uric acid amide, coconut acid amide, stearic acid amide, palmitic acid amide, behenic acid amide, brassidic acid amide, acetamide, benzamide, propionic acid amide, oleic acid amide, ricinoleic acid amide, and derivatives thereof. Among these, behenic acid amide and/or erucic acid amide are preferred from the viewpoint of the combined effect with pentaerythritol. One of these fatty acid amides may be used alone, or two or more types may be mixed and used. When two or more types of fatty acid amides are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The present expanded beads preferably contain 0.01 wt % to 1.50 wt % of fatty acid amide relative to 100 wt % of expanded beads, more preferably 0.02 wt % to 1.50 wt %, more preferably 0.02 wt % to 1.00 wt %, and even more preferably 0.50 wt % to 1.00 wt %. When the present expanded beads contain (a) 0.01 wt % or more of fatty acid amide relative to 100 wt % of P3HA-based expanded beads, the expanded beads have the advantage of being able to provide a foamed molded product with even better internal fusion properties, and when (b) 1.50 parts by weight or less is contained, the advantage is that there is no risk of inhibiting the effects of pentaerythritol.

(Additives)
In addition to the resin component containing P3HA, the expanded beads may further contain additives other than pentaerythritol and fatty acid amide (other additives). As the other additives, for example, polyalkylene glycol, crystal nucleating agent, cell regulator, lubricant, plasticizer, antistatic agent, flame retardant, conductive agent, heat insulating agent, crosslinking agent, antioxidant, ultraviolet absorber, colorant, inorganic filler, organic filler, hydrolysis inhibitor, etc. can be used according to the purpose. As the other additives, additives having biodegradability are particularly preferable. In addition, the "crystal nucleating agent" may be called "crystallization nucleating agent".

The present expanded beads preferably contain polyalkylene glycol. When the present expanded beads contain polyalkylene glycol, the expanded beads can provide a foamed molded article with excellent internal fusion properties at a low molding pressure without inhibiting the effect of adding pentaerythritol.

Examples of polyalkylene glycols include polyethylene glycol, polypropylene glycol, polybutylene glycol, and copolymers thereof. Among these, a copolymer of polyethylene glycol and polypropylene glycol (PEG-PPG copolymer) is preferred from the viewpoint of the combined effect with pentaerythritol.

Commercially available polyalkylene glycols can also be used. Examples of commercially available polyalkylene glycols include Pronon #204 and #208 manufactured by NOF Corp., Unilube 70DP-600B and Unilube 70DP-950B manufactured by NOF Corp., Emulgen PP-290 manufactured by Kao Corp., PEG #300, #600, #1000, #2000 and #6000 manufactured by NOF Corp., and PEG #400, #1000 and #1540 manufactured by Lion Specialty Chemicals Co., Ltd.

The present expanded beads preferably contain 0.01% to 1.50% by weight of polyalkylene glycol, more preferably 0.02% to 1.50% by weight, more preferably 0.02% to 1.00% by weight, and even more preferably 0.50% to 1.00% by weight, based on 100% by weight of the expanded beads. When the present expanded beads contain (a) 0.01% or more by weight of polyalkylene glycol, based on 100% by weight of the P3HA-based expanded beads, the expanded beads have the advantage of being able to provide a foamed molded product with even better internal fusion properties at a low molding pressure, and when (b) 1.50% or less by weight is contained, the advantage is that there is no risk of inhibiting the effects of pentaerythritol.

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

Therefore, the content of the crystal nucleating agent in the present expanded beads is preferably 5.0% by weight or less, more preferably 3.0% by weight or less, and even more preferably 1.5% by weight or less, based on 100 parts by weight of the expanded beads. Most preferably, the present expanded beads do not contain any crystal nucleating agent as an additional additive.

Examples of the bubble regulator 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 bubble regulators, talc is preferred because of its particularly excellent dispersibility in P3HA. Furthermore, one of these bubble regulators may be used alone, or two or more types may be mixed and used. Furthermore, when two or more types of bubble regulators are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The content of the bubble regulator in the expanded beads is not particularly limited, but is preferably 0.01% by weight to 1.00% by weight, more preferably 0.03% by weight to 0.50% by weight, and even more preferably 0.05% by weight to 0.30% by weight, relative to 100% by weight of the expanded beads.

Examples of the plasticizer include glycerin ester compounds such as glycerin diacetomonolaurate, citrate compounds such as acetyl tributyl citrate, sebacate compounds such as dibutyl sebacate, adipate compounds, polyether ester compounds, benzoate compounds, phthalate compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds such as benzyl methyl diethylene glycol adipate. Among these, glycerin ester compounds, citrate compounds, sebacate compounds, and dibasic acid ester compounds are preferred because of their particularly excellent plasticizing effect on P3HA. One of these plasticizers may be used alone, or two or more may be mixed and used. When two or more plasticizers are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The amount of plasticizer contained in the expanded beads is not particularly limited, but is preferably 1% by weight to 20% by weight, more preferably 2% by weight to 15% by weight, and even more preferably 3% by weight to 10% by weight, relative to 100% by weight of the expanded beads.

The foamed beads may contain a compound having an isocyanate group (hereinafter, may be referred to as an isocyanate compound). However, isocyanate compounds may be toxic. Furthermore, if the foamed beads contain an isocyanate compound, the resulting foamed beads and foamed molded article may turn yellow.

Therefore, the content of the isocyanate compound in the present expanded beads is preferably less than 3.0% by weight, more preferably less than 1.0% by weight, and even more preferably less than 0.1% by weight, based on 100% by weight of the expanded beads. It is most preferable that the present expanded beads do not contain any isocyanate compound.

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

<Poly(3-hydroxyalkanoate)-based resin composition and poly(3-hydroxyalkanoate)-based resin particles>
Hereinafter, each aspect of the resin composition and resin particles in one embodiment of the present invention will be described, but other than the matters detailed below, the description in the <Components> section will be used as appropriate. For example, the types and amounts of P3HA, fatty acid amide, and other additives contained in the expanded beads can be said to be the types and amounts of P3HA, fatty acid amide, and other additives contained in the resin composition and resin particles, respectively. Therefore, the types and contents of P3HA, fatty acid amide, and other additives in the resin composition and resin particles are described in the above <Components> section.

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

Here, the melting point (Tmp) of the resin particles is measured by a differential scanning calorimeter method (hereinafter referred to as the "DSC method"). The specific operating procedures are as follows: (1) 5 mg to 6 mg of resin particles are weighed out; (2) The temperature of the resin particles is raised from 10.0°C to 190.0°C at a heating rate of 10.0°C/min to melt the resin particles; (3) As shown in Figure 1, the temperature of the highest melting peak in the DSC curve of the resin particles obtained in the above step (2) can be determined as the melting point of the resin particles.

Figure 1 shows the DSC curve of P3HA-based resin particles and the melting point measured from it. The DSC curve shown in Figure 1 has one melting peak, and the temperature of the melting peak is the melting point of the resin particles.

The weight of each resin particle is not particularly limited, but is preferably 0.3 mg to 10.0 mg, and more preferably 0.5 mg to 5.0 mg. If the weight of each resin particle is 0.3 mg or more, the resin particles can be produced stably with high productivity. On the other hand, if the weight of each resin particle is 10.0 mg or less, the expanded particles obtained by expanding the resin particles can easily provide a thin-walled foamed molded article.

The shape of the resin particles is not particularly limited, but the ratio of length to diameter (length/diameter) is preferably 0.5 to 3.0, more preferably 1.5 to 2.7, and even more preferably 2.0 to 2.7. If the length/diameter of the resin particles is 0.5 to 3.0, the shape of the resulting expanded particles is not flattened, but tends to be spherical or approximately spherical. Spherical or approximately spherical expanded particles have good filling properties in the molding space of the mold of the molding machine, and can provide expanded molded products with good surface beauty. Here, the length of the resin particles refers to the maximum value of the distance between two cut surfaces that appear (are generated) on the resin particles when the resin particles are cut during the manufacturing process of the resin particles. Next, when the length direction of the resin particles is the x direction, an arbitrary straight line y and a straight line z perpendicular to the straight line y are drawn on a cross section (cross section x) perpendicular to the x direction. The line segment obtained by cutting the straight line y at the cross section x is called the line segment y, and the line segment obtained by cutting the straight line z at the cross section x is called the line segment z. The diameter of the resin particle refers to the average value of the length of line segment y and the length of line segment z.

<Physical Properties>
The physical properties of the expanded beads will now be described.

(DSC ratio)
The present expanded beads preferably have at least two melting peaks in a DSC curve obtained by differential scanning calorimetry, which will be described later. Among the melting peaks, the heat of fusion obtained from the melting peak on the higher temperature side is referred to as the "higher temperature side heat of fusion", and the heat of fusion obtained from the melting peak on the lower temperature side is referred to as the "lower temperature side heat of fusion". When there are three or more melting peaks, the heat of fusion obtained from the highest melting peak is referred to as the "higher temperature side heat of fusion", and the heat of fusion obtained from the other melting peaks is referred to as the "lower temperature side heat of fusion".

The DSC ratio of the expanded beads is not particularly limited, but is preferably 0.5% to 40.0%, more preferably 0.7% to 30.0%, even more preferably 1.0% to 25.0%, and particularly preferably 1.0% to 23.0%. When the DSC ratio of the expanded beads is 0.5% or more, there is an advantage that the expanded beads do not coalesce with each other during the expansion process. On the other hand, when the DSC ratio of the expanded beads is 40% or less, there is an advantage that a foamed molded product with excellent internal fusion tends to be obtained at a low molding pressure.

In this specification, the DSC ratio refers to the ratio of the heat of fusion on the higher temperature side to the total heat of fusion calculated from the DSC curve of the present expanded beads. In this specification, the DSC ratio is calculated by the following formula (1):
DSC ratio (%) = (high temperature side heat of fusion/total heat of fusion) x 100 (1),
In the formula (1), the high temperature side heat of fusion and the total heat of fusion are heat amounts obtained from the DSC curve of the poly(3-hydroxyalkanoate)-based expanded beads.

In this specification, the DSC curve is obtained using a differential scanning calorimeter (e.g., DSC6200 manufactured by Seiko Instruments Inc.). More specifically, in this specification, the method for measuring (calculating) the DSC ratio of the expanded beads using a differential scanning calorimeter (e.g., DSC6200 manufactured by Seiko Instruments Inc.) is as follows (1) to (6): (1) 5 mg to 6 mg of the expanded beads are weighed out; (2) The temperature of the expanded beads is raised from 10.0°C to 190.0°C at a heating rate of 10.0°C/min to melt the expanded beads; (3) As shown in Figure 2, in the DSC curve of the expanded beads obtained in the process (2) above, a straight line is drawn between the point representing the temperature before the start of melting and the point representing the temperature after the end of melting to create a baseline; (4) The DSC curve is calculated by dividing the expanded beads by the temperature before the start of melting and the temperature after the end of melting. A straight line passing through the maximum point between the melting peak or the highest melting peak and the adjacent melting peak is drawn perpendicular to the X-axis; (5) The amount of heat calculated from the high-temperature side region surrounded by the baseline, the straight line passing through the maximum point, and the DSC curve is the high-temperature side heat of fusion (J/g), the amount of heat calculated from the low-temperature side region surrounded by the baseline, the straight line passing through the maximum point, and the DSC curve is the low-temperature side heat of fusion (J/g), and the amount of heat calculated from the region surrounded by the baseline and the DSC curve is the total heat of fusion (J/g) (= high-temperature side heat of fusion + low-temperature side heat of fusion); (6) Calculate the DSC ratio from the following formula (1):
DSC ratio (%)=(high temperature side heat of fusion/total heat of fusion)×100 (1).

Figure 2 shows the DSC curve of P3HA-based expanded beads and the heat of fusion on the high-temperature side measured from the curve. The DSC curve shown in Figure 2 has two melting peaks.

The temperature (melting point) of the high-temperature melting peak or the highest melting peak in the above-mentioned DSC measurement of the expanded beads (hereinafter sometimes referred to as "Tmh") is preferably higher than the melting point (Tmp) of the resin particles before expansion. Tmh is preferably (Tmp + 3.0) ° C or higher, more preferably (Tmp + 5.0) ° C or higher, and even more preferably (Tmp + 7.0) ° C or higher. On the other hand, Tmh is preferably (Tmp + 15.0) ° C or lower, and more preferably (Tmp + 13.0) ° C or lower.

As a specific example, we will explain the case where the P3HA contained in the expanded beads is a polymer that has 3HB as an essential structural unit, and is P3HB3HH with a melting point of 145.0°C. In this case, Tmh is preferably 150.0°C to 160.0°C, and more preferably 152.0°C to 158.0°C.

Methods for controlling Tmh within the above range include, but are not limited to, methods of adjusting the foaming temperature, foaming pressure, and the time during which the resin particles are held at the foaming temperature and foaming pressure in the container before foaming. In this specification, the "time during which the resin particles are held at the foaming temperature and foaming pressure in the container before foaming" may be referred to as the "holding time."

The DSC ratio of the expanded beads is also a value that serves as a guideline for the amount of high-melting crystals contained in the expanded beads. In other words, a DSC ratio of 0.5% to 40.0% indicates that the expanded beads contain a relatively large amount of high-melting crystals. The DSC ratio of the expanded beads is also closely related to the viscoelasticity of the resin particles and the expanded beads when the resin particles are expanded and when the expanded beads are expanded. In other words, when the DSC ratio of the expanded beads is 0.5% to 40.0%, the resin particles and the expanded beads can exhibit excellent expandability and expansion properties when the resin particles are expanded and when the expanded beads are molded, respectively. As a result, the expanded beads have the advantage that they can produce expanded molded products that have excellent internal fusion properties at low molding pressure and excellent mechanical strength such as compressive strength.

In the present expanded beads, methods for controlling the DSC ratio within a predetermined range include a method for adjusting the expansion conditions (particularly the expansion temperature and expansion pressure) and/or the holding time described below, and a method for adjusting the temperature of the region (space) from which the expanded beads are released in the release step described below. In terms of ease of adjustment, a method for controlling the DSC ratio within a predetermined range is preferably a method for adjusting the expansion conditions and/or the holding time.

For example, increasing the foaming temperature tends to decrease the DSC ratio, and conversely, decreasing the foaming temperature tends to increase the DSC ratio. This is because the amount of unmelted crystals changes depending on the foaming temperature. Increasing the foaming pressure also tends to decrease the DSC ratio, and conversely, decreasing the foaming pressure tends to increase the DSC ratio. This is because the degree of plasticization changes depending on the foaming pressure, which in turn changes the amount of unmelted crystals.

In addition, the longer the holding time, the larger the DSC ratio tends to be. This is because the amount of growth of unmelted crystals changes depending on the holding time.

(Gel Fraction)
The present expanded beads are preferably produced using a crosslinking agent as described below. When produced using a crosslinking agent, the resulting expanded beads may have a crosslinked structure. That is, the present 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. When the expanded beads have a crosslinked structure, it is meant that the gel fraction of the expanded beads is 1% by weight or more relative to 100% by weight of the expanded beads.

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 good quality expanded molded articles is broadened when molding an expanded molded article, improving productivity, and when (b) 80% by weight or less, there is an advantage that expanded molded articles with excellent internal fusion can be obtained at low molding pressure.

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

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 and refluxed 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 screen; (4) the filtered product on the wire screen 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 according to the following formula:
Gel fraction (wt%)=Wg/1×100.

(density)
The density (apparent density) of the present expanded beads is not particularly limited, but is preferably 0.020 g/cm ³ to 0.600 g/cm ³ , more preferably 0.030 g/cm ³ to 0.300 g/cm ³ , and even more preferably 0.050 g/cm ³ to 0.100 g/cm ³ . When the density of the expanded beads is (a) 0.030 g/cm ³ or more, there is an advantage that an expanded molded article having excellent cushioning properties and/or mechanical strength tends to be obtained, and when it is (b) 0.600 g/cm ³ or less, there is an advantage that an expanded molded article having excellent light weight tends to be obtained. When expanded beads having a desired density cannot be obtained by only one expansion, the expanded beads expanded once may be subjected to a second or subsequent expansion step.

In this specification, the method for measuring the density of expanded beads is as follows (1) to (3): (1) prepare a graduated cylinder containing ethanol, and submerge expanded beads with a weight Wd (g) in the ethanol; (2) determine the volume of the expanded beads as determined from the rise in the water level of the ethanol (submersion method) as Vd (cm ³ ); (3) calculate the density of the expanded beads by the following formula:
Density (g/cm ³ )=Wd/Vd.

The shape of the present expanded beads is not particularly limited, but the ratio of length to diameter (length/diameter) is preferably 1.0 to 2.0, and more preferably 1.0 to 1.5. If the length/diameter of the expanded beads is 1.0 to 2.0, it has the advantage that the filling property into the molding space of the mold of the molding machine is good, and an expanded molded body with good surface beauty can be obtained. Furthermore, as the length/diameter of the expanded beads approaches 1.0 to 1.2, especially as it approaches 1.0, the gap between the expanded beads tends to become smaller in the expanded molded body obtained from the expanded beads, and as a result, it has the advantage that the cushioning properties and/or mechanical strength are excellent. Here, the length of the present expanded beads means the length that is the straight line distance between two points selected arbitrarily so that the straight line distance between the two points is the longest on the expanded beads. Next, when the length direction of the expanded beads is the x direction, an arbitrary straight line y and a straight line z perpendicular to the straight line y are drawn on a cross section (cross section x) perpendicular to the x direction. The line segment obtained by cutting the straight line y at the cross section x is called the line segment y, and the line segment obtained by cutting the straight line z at the cross section x is called the line segment z. The diameter of the present expanded beads refers to the average value of the length of the line segment y and the length of the line segment z.

[3. Method for producing expanded poly(3-hydroxyalkanoate)-based particles] The method for producing expanded poly(3-hydroxyalkanoate)-based particles according to one embodiment of the present invention includes a foaming step of foaming poly(3-hydroxyalkanoate)-based resin particles containing 100 parts by weight of poly(3-hydroxyalkanoate) and 0.01 to 20.00 parts by weight of pentaerythritol, and the foaming step includes a dispersing step of dispersing the poly(3-hydroxyalkanoate)-based resin particles in an aqueous dispersion medium.

In this specification, the "method for producing poly(3-hydroxyalkanoate) (P3HA)-based expanded beads" may be referred to as the "production method," and the "method for producing poly(3-hydroxyalkanoate) (P3HA)-based expanded beads according to one embodiment of the present invention" may be referred to as the "present production method."

Because this manufacturing method has the above-mentioned configuration, it has the advantage of being able to provide foamed particles that can produce foamed molded articles with excellent internal fusion at low molding pressures.

A specific embodiment of the method for producing P3HA-based expanded beads according to one embodiment of the present invention is, for example, a production method that includes, in order, a resin particle preparation step for preparing resin particles and an expansion step for expanding the resin particles, but is not limited to such a production method.

(Resin particle preparation process)
The present manufacturing method preferably includes a resin particle preparation step of preparing P3HA-based resin particles containing 100 parts by weight of a P3HA-based resin and 0.01 to 20.00 parts by weight of pentaerythritol prior to the foaming step. The resin particle preparation step can also be said to be a step of forming a resin composition 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 process includes:
(a) a melt-kneading step of melt-kneading a resin composition containing 100 parts by weight of P3HA and 0.01 to 20.00 parts by weight of pentaerythritol;
It is preferable that the method further comprises (b) a particle forming step of forming the melt-kneaded resin composition into a shape that is easily usable for foaming.

The present inventors have independently and surprisingly found that pentaerythritol may be eluted from the resin particles in the dispersion step of the present manufacturing method, which will be described later. The amount of pentaerythritol eluted from the resin particles in the dispersion step may vary depending on the conditions of the dispersion step and the time required. In the resin particle preparation step, it is preferable to adjust the amount of pentaerythritol used so that the pentaerythritol content contained in the finally obtained expanded particles is a desired value, taking into account the amount of pentaerythritol eluted from the resin particles in the subsequent dispersion step. On the other hand, according to the present manufacturing method, expanded particles containing 0.01% to 4.50% by weight of pentaerythritol per 100% by weight of expanded particles can be obtained relatively easily.

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 100 parts by weight of P3HA, 0.01 to 20.00 parts by weight of pentaerythritol, and, if necessary, fatty acid amide and/or other 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 100 parts by weight of P3HA, 0.01 to 20.00 parts by weight of pentaerythritol, and, as necessary, fatty acid amide and/or other additives are supplied to a melt kneading apparatus, and a resin composition is prepared (completed) in the melt kneading apparatus, and the resin composition is melt kneaded.

In the method (a1) above, the order in which 100 parts by weight of P3HA, 0.01 to 20.00 parts by weight of pentaerythritol, and, if necessary, fatty acid amide and/or other additives are mixed or blended (dry blended) is not particularly limited. In the method (a2) above, the order in which 100 parts by weight of P3HA, 0.01 to 20.00 parts by weight of pentaerythritol, and, if necessary, fatty acid amide and/or other additives are supplied to the melt kneading device is not particularly limited.

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

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

In the method (a1), the amount of pentaerythritol, fatty acid amide, and other additives used for mixing or blending is the content of pentaerythritol, fatty acid amide, and other additives in the resulting resin particles. In the method (a2), the amount of pentaerythritol, fatty acid amide, and other additives supplied to the melt kneading device is the content of pentaerythritol, fatty acid amide, and other additives in the resulting resin particles. Therefore, the above-mentioned (pentaerythritol), (fatty acid amide), and (other additives) sections are used to describe the amount of pentaerythritol, fatty acid amide, and other additives used and the amount of other additives supplied. It is not necessary to use all of the other additives used in this manufacturing method in the resin particle preparation step. In other words, all or a part of the other additives used in this manufacturing method (e.g., crosslinking agent, plasticizer, etc.) may be added to the dispersion in the subsequent dispersion step without being used in the resin particle preparation step, i.e., without being contained in the resin particles.

In the melt-kneading process, the temperature at which the resin composition is melt-kneaded cannot be generally specified because it depends on the physical properties of P3HA (melting point, weight average molecular weight, etc.) and the type of additive used. Regarding the temperature at which the resin composition is melt-kneaded, for example, the temperature of the melt-kneaded resin composition discharged from the nozzle of the die (hereinafter sometimes referred to as the composition temperature) is preferably 150°C to 200°C, more preferably 160°C to 195°C, and even more preferably 170°C to 190°C. If the composition temperature is 150°C or higher, there is no risk of the resin composition being insufficiently melt-kneaded. On the other hand, if the composition temperature is 200°C or lower, there is no risk of P3HA thermal decomposition.

The form of the particle molding process is not particularly limited as long as the melt-kneaded resin composition can be molded into a 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 a desired shape in the particle molding process. Specifically, the melt-kneaded resin composition can be molded into a desired shape by discharging the melt-kneaded resin composition from a nozzle of a die equipped in the melt-kneading device and cutting the resin composition with a cutting device at the same time as or after discharging. The shape of the obtained resin particles is not particularly limited, but cylindrical, elliptical, spherical, cubic, rectangular, etc. are preferred because they are easy to use for foaming.

In the particle molding process, the resin composition discharged from the die nozzle may be cooled. When the resin composition discharged from the die nozzle is cooled, the resin composition may be cut by a cutting device at the same time as or after cooling.

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

(Foaming process)
The form of the foaming step in this production method is not particularly limited as long as it can foam the resin particles. In one embodiment of the present invention, the foaming step may include a dispersing step of dispersing poly(3-hydroxyalkanoate)-based resin particles in an aqueous dispersion medium. The specific form of the dispersing step is not particularly limited, but the dispersing step is, for example, a step of dispersing resin particles, an aqueous dispersion medium, a crosslinking agent, a foaming agent, and, if necessary, a dispersant, a crosslinking assistant, a dispersion assistant, and/or a plasticizer in a container. The foaming step is a step other than the dispersing step, which follows the dispersing step:
(a) 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;
(b) maintaining the temperature and pressure in the container at constant temperature and pressure;
(c) a discharging step of opening one end of the container and discharging the dispersion in the container into a region (space) having a pressure lower than the foaming pressure (i.e., the pressure inside the container).

(Dispersion process)
The dispersion step can be said to be, for example, a step of preparing a dispersion liquid in which resin particles, a crosslinking agent, a foaming agent, and optionally a dispersing agent, a crosslinking aid, a dispersion aid, and/or a plasticizer are dispersed in an aqueous dispersion medium. In the dispersion liquid, (a) the crosslinking agent and the crosslinking aid are consumed by the reaction with P3HA in the resin particles and may not be present, and (b) the foaming agent and the plasticizer are impregnated in the resin particles and may not be present in a dispersed state.

The container is not particularly limited, but is preferably one that can withstand the foaming temperature and foaming pressure described below, e.g., a pressure-resistant container.

The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse the resin particles, crosslinking agent, foaming agent, etc. As the aqueous dispersion medium, for example, tap water and/or industrial water can be used. In terms of enabling stable production of foamed particles, it is preferable to use pure water such as RO water (water purified by reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin), and ultrapure water as the aqueous dispersion medium.

The amount of aqueous dispersion medium used is not particularly limited, but is preferably 100 to 1,000 parts by weight per 100 parts by weight of resin particles.

In this manufacturing method, it is preferable to use a crosslinking agent. By using a crosslinking agent, the P3HA in the resulting expanded beads becomes P3HA with a crosslinked structure. In other words, P3HA expanded beads with an excellent gel fraction can be obtained. As a result, (a) when molding a foamed molded product, the molding temperature range of the expanded beads that can provide a good quality foamed molded product is broadened, improving productivity, and (b) there are advantages in that a foamed molded product with excellent internal fusion can be obtained at a low molding pressure. In the foaming process, the crosslinking reaction of the P3HA in the resin particles also progresses, so the foaming process can also be called a crosslinking process.

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, it is preferable that the poly(3-hydroxyalkanoate)-based expanded particles are crosslinked by an organic peroxide. The organic peroxide may be used in (a) the resin particle manufacturing process, (b) the dispersion process, or (c) the resin particle manufacturing process and the dispersion process. More specifically, in order to react the organic peroxide with P3HA, (a) the organic peroxide and P3HA may be melt-kneaded in the resin particle manufacturing process, (b) the resin particles and the organic peroxide may be dispersed in an aqueous dispersion medium in the dispersion process, or (c) the organic peroxide and P3HA may be melt-kneaded and the resin particles and the organic peroxide may be dispersed in an aqueous dispersion medium. In the dispersion process, the resin particles manufactured in the resin particle manufacturing process and the organic peroxide are dispersed in an aqueous dispersion medium, so that the organic peroxide can be impregnated and reacted with the resin particles. For these reasons, organic peroxides are preferred as crosslinking agents in the manufacturing method of the present expanded beads. 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) to form a crosslinked structure.

Although it depends on the type of P3HA used, the organic peroxide used as the crosslinking agent is preferably an organic peroxide with a half-life temperature of 90°C to 160°C, more preferably an organic peroxide with a half-life temperature of 110°C to 160°C, even more preferably an organic peroxide with a half-life temperature of 110°C to 125°C, and particularly preferably an organic peroxide with a half-life temperature of 114°C to 124°C. Specific examples of such organic peroxides include benzoyl peroxide (BPO, half-life temperature: 92°C), t-butylperoxy-2-ethylhexyl carbonate (TBEC, half-life temperature: 121°C), t-butylperoxyisopropyl carbonate (TBIC, half-life temperature: 118°C), t-amylperoxy-2-ethylhexyl carbonate (TAEC, half-life temperature: 117°C), t-amylperoxyisopropyl carbonate (TA IC, 1-hour half-life temperature: 115°C), t-butyl peroxyisobutyrate (1-hour half-life temperature: 93°C), t-butyl peroxy-2-ethylhexanoate (1-hour half-life temperature: 95°C), t-butyl peroxyisononanoate (1-hour half-life temperature: 123°C), t-butyl peroxyacetate (1-hour half-life temperature: 123°C), t-butyl peroxydibenzoate (1-hour half-life temperature: 125°C), t-amyl peroxyisobutyrate (1-hour half-life Temperature: 93°C), t-amylperoxy-2-ethylhexanoate (1-hour half-life temperature: 92°C), t-amylperoxyisononanoate (1-hour half-life temperature: 114°C), t-amylperoxyacetate (1-hour half-life temperature: 120°C), t-amylperoxybenzoate (1-hour half-life temperature: 122°C), dicumyl peroxide (1-hour half-life temperature: 137°C), 2,5-dimethyl-2,5-di(t-butylperoxy)hexane (1-hour half-life temperature: 140°C), di-t-butyl peroxide (1-hour half-life temperature: 149°C), 1,1-di(t-butylperoxy)cyclohexane (1-hour half-life temperature: 116°C), 2,2-di(t-butylperoxy)butane (1-hour half-life temperature: 127°C), 1,1-di(t-amylperoxy)cyclohexane (1-hour half-life temperature: 112°C), 1,1-di(t-butylperoxy)3,3,5-trimethylcyclohexane (1-hour half-life temperature: 114°C), etc. When an organic peroxide with a 1-hour half-life temperature of 90°C or higher is used, there is an advantage that there is a tendency to obtain expanded beads with a desired gel fraction. On the other hand, when an organic peroxide with a 1-hour half-life temperature of 160°C or lower is used, there is an advantage that there is no risk of unreacted crosslinking agent remaining in the final product.

The amount of the 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, and even more preferably 0.5 to 2.5 parts by weight, relative to 100 parts by weight of the resin particles. When the amount of the crosslinking agent used is 0.1 parts by weight or more relative to 100 parts by weight of the resin particles, (a) the obtained expanded beads can be sufficiently crosslinked, and (b) the closed cell ratio of the obtained expanded beads is high, and an expanded molded product with good surface beauty and small molding shrinkage can be obtained. On the other hand, when the amount of the crosslinking agent used is 5.0 parts by weight or less relative to 100 parts by weight of the resin particles, the effect according to the amount of the crosslinking agent added can be obtained, so there is no risk of economic waste. The amount of the crosslinking agent used is positively correlated with the gel fraction of the expanded beads and greatly affects the value of the gel fraction of the expanded beads. Therefore, it is desirable to strictly set the amount of the crosslinking agent used in consideration of the gel fraction of the expanded beads obtained. The resin particles used in the dispersion step may already contain a crosslinking agent, in which case it is preferable that the total amount of the crosslinking agent already contained in the resin particles before the dispersion step and the amount of the crosslinking agent used in the dispersion step falls within the above range.

Examples of the blowing agent 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. As the blowing agent, at least one selected from the group consisting of the above-mentioned inorganic gases, saturated hydrocarbons having 3 to 5 carbon atoms, ethers, halogenated hydrocarbons, and water can be used. Among them, from the viewpoint of environmental load and foaming power, it is preferable to use nitrogen or carbon dioxide as the blowing agent. One of these blowing agents may be used alone, or two or more may be mixed and used. In addition, when two or more blowing agents are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The amount of foaming agent used is not particularly limited, but is preferably 2 parts by weight to 10,000 parts by weight, more preferably 5 parts by weight to 5,000 parts by weight, and even more preferably 10 parts by weight 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, an effect according to the amount of foaming agent used is obtained, so no economic waste occurs.

In this manufacturing method, it is preferable to use a dispersant. The use of a dispersant has the advantage that adhesion between resin particles (sometimes called blocking) can be suppressed, and expanded particles can be stably manufactured. 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 mixed and used. When two or more dispersants are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The amount of the dispersant used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight, more preferably 0.5 to 1.5 parts by weight, relative to 100 parts by weight of the resin particles. In this manufacturing method, a crosslinking assistant may be used to improve the crosslinking efficiency of P3HA. Examples of the crosslinking assistant include compounds having at least one unsaturated bond in the molecule. Among the compounds, allyl esters, acrylic esters, methacrylic esters, divinyl compounds, and the like are particularly preferred. One type of these crosslinking assistants may be used alone, or two or more types may be mixed and used. In addition, when two or more types of crosslinking assistants are mixed and used, the mixing ratio may be appropriately adjusted according to the purpose.

The amount of the cross-linking aid used is not particularly limited, but is preferably 0.01 to 3.00 parts by weight, more preferably 0.03 to 1.50 parts by weight, and even more preferably 0.05 to 1.00 parts by weight, per 100 parts by weight of the resin particles. If the amount of the cross-linking aid used is 0.01 part by weight or more per 100 parts by weight of the resin particles, it will be sufficiently effective as a cross-linking aid.

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

In this manufacturing method, a dispersing aid may be used to improve the effect of suppressing adhesion between resin particles. Examples of dispersing aids include anionic surfactants such as sodium alkane sulfonate, sodium alkylbenzene sulfonate, and sodium α-olefin sulfonate. One of these dispersing aids may be used alone, or two or more may be mixed and used. When two or more dispersing aids are mixed, the mixing ratio may be appropriately adjusted depending on the purpose.

The amount of the dispersing aid 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, per 100 parts by weight of resin particles. In order to further improve the effect of suppressing adhesion between resin particles, it is preferable to use the dispersing agent and the dispersing aid in combination.

In this manufacturing method, a plasticizer may be used. The use of a plasticizer has the advantage that it is easier to reduce the density of the expanded beads, i.e., it is easier to increase the expansion ratio of the expanded beads.

The plasticizers used in this manufacturing method, or the plasticizers that are preferably used, include those described in the (Additives) section of the <Components> section of [2. Poly(3-hydroxyalkanoate)-based expanded particles] above.

The amount of plasticizer used is not particularly limited, but is preferably more than 0 parts by weight and not more than 20 parts by weight, more preferably 1 to 15 parts by weight, and even more preferably 1 to 10 parts by weight, per 100 parts by weight of resin particles. The resin particles used in the dispersion process may already contain a plasticizer before the dispersion process. If the resin particles used already contain a plasticizer before the dispersion process, it is preferable that the total amount of the plasticizer already contained in the resin particles before the dispersion process and the amount of plasticizer used in the dispersion process falls within the above range.

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

The foaming temperature cannot be generally defined because it varies depending on the type of P3HA, the type of foaming agent, the apparent density of the desired foamed beads, etc. The foaming temperature is preferably lower than the temperature (Tmh) of the high-temperature melting peak or the highest melting peak in the above-mentioned DSC measurement of the resulting foamed beads, and is preferably lower than the melting point (Tmp) of the resin particles before foaming. For example, the foaming temperature is preferably (Tmp-40.0)°C to Tmp°C, more preferably (Tmp-30.0)°C to (Tmp-10.0)°C, even more preferably (Tmp-20.0)°C to (Tmp-15.0)°C, and most preferably (Tmp-19.0)°C to (Tmp-16.0)°C. When the foaming temperature is (Tmp-40.0)°C or higher, foamed beads with a suitable density tend to be obtained. On the other hand, if the foaming temperature is equal to or lower than Tmp°C, there is no risk of hydrolysis of the resin particles occurring in the container. The foaming temperature is correlated with the DSC ratio of the resulting foamed beads, and greatly affects the value of the DSC ratio. Therefore, it is desirable to set the foaming temperature strictly, taking into account the DSC ratio of the resulting foamed beads.

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

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

In the holding step, the time for which the dispersion in the container is held at near the foaming temperature and foaming pressure is not particularly limited. The "time for which the dispersion in the container is held at near the foaming temperature and foaming pressure" can also be called the "holding time" explained in the section (DSC ratio). The holding time is preferably 1 minute to 60 minutes, and more preferably 5 minutes to 45 minutes. If the holding time is 1 minute or more, the DSC ratio can be easily controlled within a predetermined range, and there is no risk of unreacted crosslinking agent remaining. On the other hand, if it is 60 minutes or less, there is no risk of excessive hydrolysis of the P3HA contained in the resin particles.

(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 be expanded, and as a result, expanded particles are obtained.

In the release process, the "region under pressure lower than the foaming pressure" refers to an "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.

In the releasing step, when releasing the dispersion into a region with a pressure lower than the expansion pressure, the dispersion can be released through an opening orifice with a diameter of 1 mm to 5 mm for the purpose of adjusting the flow rate of the dispersion and reducing the variation in the expansion ratio of the resulting expanded particles. In addition, when using resin particles with a relatively high melting point, the low-pressure region (space) can be filled with saturated water vapor for the purpose of improving the expandability.

As mentioned above, in the foaming process, pentaerythritol in the resin particles may dissolve into the aqueous dispersion medium. The amount of pentaerythritol dissolved in the resin particles during the foaming process cannot be generalized because it varies depending on the conditions of the foaming process and the time required, but it is generally about 0.1% to 99% of the amount of pentaerythritol contained in the resin composition or resin particles. Therefore, it is preferable to investigate the amount of pentaerythritol dissolved under specified conditions of the foaming process in advance and adjust the amount of pentaerythritol in the resin particles to be used under those conditions based on the results (amount of dissolved pentaerythritol). This makes it possible to easily obtain foamed particles with the desired pentaerythritol content.

There is no particular limitation on the method for quantifying the pentaerythritol content in the expanded beads. The pentaerythritol content in the expanded beads can be analyzed by an analytical institution or the like. The pentaerythritol content in the expanded beads can be measured, for example, by the following methods (1) to (3): (1) 20 mg of the expanded beads are completely dissolved in 0.8 ml of chloroform; (2) 1.6 ml of heavy water containing 1.6 mg of (sodium 3-(trimethylsilyl)propionate-2,2,3,3-d4) as an internal standard is added to the chloroform, and a separation operation is performed to transfer the pentaerythritol in the expanded beads to the heavy water layer; (3) ¹ (a) NMR spectra of 1.6 mg to 9.6 mg (1.6 mg, 5.0 mg, 7.0 mg, 9.6 mg) of pentaerythritol standards and (b) the amount of pentaerythritol in the heavy water layer extracted in (2) (containing 1.6 mg of (sodium 3-(trimethylsilyl)propionate-2,2,3,3-d4)) are measured by H-NMR; (4) the amount of pentaerythritol in the heavy water layer is quantified based on a calibration curve obtained from the measurement results of the pentaerythritol standards, and this is regarded as the amount of pentaerythritol contained in the expanded particles. This method is sometimes called a liquid separation method.

Note that expanded beads using a crosslinking agent may not completely dissolve in an organic solvent. Therefore, when calculating the pentaerythritol content in expanded beads X obtained using a crosslinking agent, the procedure is as follows: (1) Expanded beads are produced under the same conditions as those for producing expanded beads X, except that no crosslinking agent is used, to obtain expanded beads Y; (2) The amount of pentaerythritol in expanded beads Y is quantified; (3) The pentaerythritol content in expanded beads Y is regarded as the pentaerythritol content in expanded beads X.

In addition, there is little risk that components other than pentaerythritol contained in the resin particles (e.g., fatty acid amides, etc.) will dissolve from the resin particles during the dispersion process. Therefore, for components other than pentaerythritol contained in the resin particles, an arithmetic calculation can be made from the number of parts added or supplied per 100 parts by weight of P3HA, and the result obtained can be used as the content in the expanded beads.

The present expanded beads are most preferably produced by the above-mentioned production method, but are not limited thereto. For example, the present expanded beads can be obtained by the production methods described in the following (r1) to (r3):
(r1) The resin particles obtained by the (resin particle preparation process) are placed in a pressure vessel, and a blowing agent is pressurized into the pressure vessel without using an aqueous dispersion medium. The pressure vessel is heated and maintained at a temperature as necessary to obtain resin particles containing a blowing agent. Next, the pressure vessel is depressurized to return to atmospheric pressure, and the resin particles containing a blowing agent are then heated in the pressure vessel or transferred to another pressure vessel and heated with a heating means such as steam to expand the resin particles impregnated with the blowing agent to obtain expanded particles;
(r2) In the (melt kneading step) of the (resin particle preparation step), when the resin composition is melt kneaded, a crosslinking agent and a foaming agent are pressed into the melt kneading device to prepare a resin composition containing the crosslinking agent and the foaming agent. The resin composition is then discharged from a nozzle of a die provided in the melt kneading device, and while cooling at the same time as being discharged, the resin composition is cut by a cutting device to obtain resin particles containing a foaming agent. The resin particles are transferred to a pressure-resistant container, heated by a heating means such as steam, and the resin particles are foamed to obtain foamed particles;
(r3) In the (melt-kneading step) of the (resin particle preparation step), when the resin composition is melt-kneaded, a crosslinking agent and a foaming agent are pressed into the melt-kneading device to prepare a resin composition containing the crosslinking agent and the foaming agent. The resin composition is then discharged from a nozzle of a die provided in the melt-kneading device, and the resin composition is foamed at the same time as being discharged and cut by a cutting device to obtain expanded particles.

In the above (r1), the pressure at which the foaming agent is injected into the pressure vessel is preferably 0.01 MPa (gauge pressure) to 10.00 MPa (gauge pressure), and more preferably 0.03 MPa (gauge pressure) to 5.00 MPa (gauge pressure).

In the above (r1) and (r2), the temperature inside the pressure vessel when the resin particles containing the foaming agent are heated by steam or the like is preferably 100°C to 150°C, and more preferably 105°C to 145°C.

In the above (r2) and (r3), the pressure at which the crosslinking agent and the foaming agent are injected into the melt kneading device is preferably 3 MPa (gauge pressure) to 30 MPa (gauge pressure), and more preferably 5 MPa (gauge pressure) to 15 MPa (gauge pressure).

The manufacturing methods (r1) to (r3) do not use an aqueous dispersion medium, so the pentaerythritol contained in the resin particles does not dissolve during the manufacturing process of the expanded beads. In other words, it can be said that the amount of pentaerythritol contained in the resin particles is the amount of pentaerythritol contained in the expanded beads. Therefore, in the manufacturing methods (r1) to (r3), it is preferable to adjust the amount of pentaerythritol contained in the resin particles, that is, the amount of pentaerythritol used in the melt-kneading process, to the same amount as the desired amount of pentaerythritol contained in the expanded beads (for example, 0.01 to 4.50 parts by weight per 100 parts by weight of P3HA).

(Two-stage foaming process)
In the present manufacturing method, the foaming step alone may not provide expanded beads with a desired apparent density. In that case, the present manufacturing method may further include a second-stage foaming step in which the expanded beads obtained in the foaming step are further expanded. The second-stage foaming step is not particularly limited as long as the expanded beads obtained in the foaming step are further expanded to provide expanded beads with an apparent density smaller than that of the expanded beads obtained in the foaming step. Examples of the second-stage foaming step include the following: (s1) supplying the expanded beads obtained in the foaming 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 by the above (s2), and increasing the pressure inside the expanded beads (hereinafter sometimes referred to as "expanded bead internal pressure") to a level higher than normal pressure; (s4) thereafter, heating the expanded beads with water vapor or the like to further expand them to obtain expanded beads with a desired apparent density. The expanded beads obtained in the two-stage foaming step may be 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.

In the two-stage expansion process, the internal pressure of the expanded particles is preferably 0.15 MPa (absolute pressure) to 0.60 MPa (absolute pressure), and more preferably 0.30 MPa (absolute pressure) to 0.60 MPa (absolute pressure).

In the two-stage expansion process (steps s2 and s3), the temperature inside the container when the expanded particles are impregnated with the inorganic gas is preferably 10°C to 90°C, more preferably 20°C to 90°C, and even more preferably 40°C to 90°C.

In the second-stage expansion step (step s4 above), the pressure of the steam or the like used to heat the expanded particles (hereinafter, sometimes referred to as the "second-stage expansion pressure") varies depending on the properties of the expanded particles 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).

It is preferable that the DSC ratio, gel fraction, and apparent density of the second-stage expanded particles are the same as those of the expanded particles. In other words, the descriptions in the above (DSC ratio), (gel fraction), and (density) sections can be used as appropriate for the DSC ratio, gel fraction, and apparent density of the second-stage expanded particles.

The method for producing poly(3-hydroxyalkanoate)-based expanded beads according to another embodiment of the present invention may be configured as follows: The method for producing poly(3-hydroxyalkanoate)-based expanded beads described in section [2. Poly(3-hydroxyalkanoate)-based expanded beads] includes a foaming step of foaming poly(3-hydroxyalkanoate)-based resin particles containing 100 parts by weight of poly(3-hydroxyalkanoate) and 0.01 to 20.00 parts by weight of pentaerythritol.

[4. P3HA-based foamed molded body]
The poly(3-hydroxyalkanoate)-based expanded molded article according to one embodiment of the present invention is an expanded molded article obtained by molding the poly(3-hydroxyalkanoate)-based expanded beads described in Section 2. Poly(3-hydroxyalkanoate)-based expanded beads. This expanded molded article can also be said to be an expanded molded article containing the expanded beads described in Section 2. Poly(3-hydroxyalkanoate)-based expanded beads.

Because the foamed molded product has the above-mentioned configuration, it has the advantage of excellent internal fusion. In this specification, the internal fusion property of the foamed molded product is evaluated by the internal fusion rate. The foamed molded product preferably has an internal fusion rate of 80% or more, more preferably 85% or more, even more preferably 90% or more, even more preferably 95% or more, and most preferably 100%. A foamed molded product with an internal fusion rate of 80% or more has the advantage of excellent impact resistance.

In this specification, the internal fusion rate is a value measured by the following methods (1) to (4): (1) making a cut in any one surface of the foamed molded article in the vertical direction with a cutter, the cut being 1/20 to 1/5 of the vertical thickness of the part having that surface; (2) then breaking the foamed molded article by hand along the cut; (3) visually observing the obtained fracture surface within an area of 5 mm to 50 mm vertically (in the thickness direction) x 10 mm to 200 mm horizontally, excluding the cut portion and including the center in the thickness direction, to count the number of all foamed beads present within that area, and the number of foamed beads that are broken within that area other than at the particle interfaces (i.e., foamed beads that are broken within the foamed beads themselves); (4) calculating the internal fusion rate based on the following formula (4):
Internal fusion rate (%)=(number of expanded particles broken at other than particle interfaces within the range of 5 mm to 50 mm in length (thickness direction) × 10 mm to 200 mm in width/total number of expanded particles present within the range) × 100 (4).

It is preferable that the foamed molded article has portions with different dimensions (lengths) in at least one of the X, Y, and Z directions.

As described below, in the production of the present foam molded product, a mold may be used that has a fixed mold that cannot be driven and a movable mold that can be driven relative to the fixed mold. When producing a foam molded product using such a mold, the drive direction of the movable mold is the thickness direction of the resulting foam molded product. When producing a foam molded product using such a mold, it is preferable that the resulting foam molded product has one or more regions in the thickness direction of the foam molded product selected from the group consisting of a first region where the movable mold used to produce the foam molded product enters the foam molded product, and a second region where the foam molded product enters the movable mold.

(a) A foamed molded product having a region with different dimensions (lengths) in at least one of the X, Y, and Z directions, or (b) a foamed molded product having one or more regions in the thickness direction of the foamed molded product selected from the group consisting of a first region where the movable mold used to produce the foamed molded product enters the foamed molded product and a second region where the foamed molded product enters the movable mold, can also be said to have a foamed molded product with a complex shape. When a foamed molded product having a complex shape as described above is produced using foamed beads obtained by conventional technology, the internal fusion rate of the resulting foamed molded product may be reduced depending on the region of the foamed molded product. However, when a foamed molded product having a complex shape is produced using the present foamed beads, the resulting foamed molded product has the advantage of having a high internal fusion rate in all regions.

An example of this foam molded product, specifically an example of a foam molded product having a complex shape as described above, is shown in Figures 3 and 4. Figure 3 is a perspective view of a P3HA-based foam molded product 100 according to one embodiment of the present invention, viewed from one direction. Figure 4 is a cross-sectional view taken along line A-A in Figure 3.

As described later, the P3HA foam molded body 100 is manufactured by a mold having a fixed mold that cannot be driven and a movable mold that can be driven. The X direction of the P3HA foam molded body 100 is the driving direction of the movable mold. As shown in FIG. 4, the P3HA foam molded body 100 has a bottom portion having a length of H ₁ and a standing wall portion having a length of H ₂ in the driving direction of the movable mold. H ₁ and H ₂ are different in length. That is, the P3HA foam molded body 100 (a) has a portion having a different dimension (length) in the X direction, (b) has a portion having a different length in the driving direction of the movable mold, and (c) has a first region in the thickness direction of the foam molded body where the movable mold used to manufacture the foam molded body enters the foam molded body or a second region where the foam molded body enters the movable mold.

5. Method for producing poly(3-hydroxyalkanoate)-based foamed molded article
The method for producing a poly(3-hydroxyalkanoate)-based expanded molded article according to one embodiment of the present invention includes a filling step of filling a molding space formed by at least two molds of a mold with the poly(3-hydroxyalkanoate)-based expanded beads described in the section [2. Poly(3-hydroxyalkanoate)-based expanded beads], and a fusion step of heating the filled poly(3-hydroxyalkanoate)-based expanded beads to fuse the poly(3-hydroxyalkanoate)-based expanded beads together.

The method for producing a P3HA-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 foam molded article with excellent internal fusion properties.

In one embodiment of the present invention, a method for producing a P3HA-based foam molded article preferably uses a mold that includes 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. It is more preferable that the fixed mold and the movable mold are capable of forming a molding space in which portions of different lengths are formed in the driving direction of the movable mold.

A mold equipped with a fixed mold and a movable mold capable of forming a molding space in which a portion of different lengths is formed in the driving direction of the movable mold is designated as mold X. The molding space in mold X is designated as molding space X. The portions in molding space X with different lengths in the driving direction of the movable mold have (a) a difference in the amount of foamed beads filled, and (b) a difference in the distance that water vapor moves during molding, compared to other portions. Therefore, when a foamed molded body is manufactured using conventional foamed beads and mold X, (a) there is a case where the filling rate of the conventional foamed beads in molding space X varies, and (b) there is a case where water vapor passes unevenly through the filled foamed beads. As a result, in a foamed molded body manufactured using conventional foamed beads and mold X, the internal fusion rate may be reduced depending on the portion of the foamed molded body. On the other hand, the present foamed molded body manufactured using the present foamed beads and mold X has the advantage that the internal fusion rate is high in all portions of the foamed molded body.

A specific embodiment of the method for producing a P3HA-based foamed molded article according to one embodiment of the present invention is, for example, a production method (in-mold foaming method) including the following (b1) to (b6) in order, but is not limited to such a production method:
(b1) A mold consisting of a fixed mold that cannot be driven and a movable mold that can be driven is mounted on an in-mold foam molding machine, where the fixed mold and the movable mold are capable of forming a closed space inside the fixed mold and the movable mold, in which portions of different lengths are formed in the driving direction of the movable mold, when the movable mold is driven toward the fixed mold (this operation may be referred to as "mold closing");
(b2) The movable mold is driven toward the fixed mold so that the fixed mold and the movable mold are not completely closed, and a small gap (for example, a gap of 10 mm in the thickness direction of the bottom of the foam molded body or in the height direction of the upright wall part (also called cracking)) is formed;
(b3) Filling the molding space formed inside the fixed mold and the movable mold with expanded particles that have not been pressurized with air, for example, through a filling machine;
(b4) driving the movable mold so that the fixed mold and the movable mold are completely closed (i.e., completely closing the molds);
(b5) After preheating the mold with steam, the mold is one-sidedly heated and reverse-sidedly heated with steam, and further the mold is double-sidedly heated with steam, thereby performing in-mold foaming;
(b6) The in-mold foamed product is removed from the mold and dried (for example, at 75° C.) to obtain a foamed molded product.

In (b5) above, the "water vapor pressure during one-sided heating and reverse one-sided heating" is "water vapor pressure A" and the "water vapor pressure during double-sided heating" is "water vapor pressure B".

The pressure of the water vapor 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 product with a high internal fusion rate tends to be obtained. In particular, it is preferable to set the water vapor pressure A to about half the pressure of the water vapor pressure B during in-mold foam molding, since excessive pressurization is not required, it is economically advantageous, and a foamed molded product with a high internal fusion rate can be provided.

In this specification, the water vapor pressure B in the manufacturing method of P3HA-based foam molded products is referred to as the "molding pressure." In the manufacturing method of P3HA-based foam molded products according to one embodiment of the present invention, by using the foam particles described in section [2. Poly(3-hydroxyalkanoate)-based foam particles], a foam molded product with excellent internal fusion properties can be provided at a lower molding pressure than conventional techniques. In other words, in the manufacturing method of P3HA-based foam molded products according to one embodiment of the present invention, a foam molded product with excellent internal fusion properties can be provided at a lower minimum molding pressure than conventional techniques.

In this specification, the minimum molding pressure in the method for producing a P3HA-based foamed molded product is a value measured by the following methods (1) to (3):
(1) The water vapor pressure B is changed in increments of 0.01 MPa (gauge pressure) between 0.10 MPa (gauge pressure) and 0.20 MPa (gauge pressure), and the water vapor pressure A is set to 1/2 the water vapor pressure B, and at each water vapor pressure B, the foamed beads are foamed in a mold to obtain a foamed molded article; (2) The internal fusion rate is measured for each foamed molded article; (3) The lowest pressure among the water vapor pressures B at which a foamed molded article with the highest internal fusion rate is obtained is defined as the minimum molding pressure. The method for measuring the internal fusion rate is as described above.

The water vapor pressure B is preferably 0.15 MPa (gauge pressure) or less, more preferably 0.14 MPa (gauge pressure) or less, and even more preferably 0.13 MPa (gauge pressure) or less. The lower the water vapor pressure B, the smaller the economic burden. The lower limit of the water vapor pressure B is not particularly limited, but is preferably 0.08 MPa (gauge pressure) or more, and more preferably 0.10 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 product with a high internal fusion rate and excellent impact resistance tends to be obtained.

In one embodiment of the present invention, the smaller the minimum molding pressure, the more preferable; for example, 0.15 MPa (gauge pressure) or less is preferable, 0.14 MPa (gauge pressure) or less is more preferable, and 0.13 MPa (gauge pressure) or less is even more preferable. When the minimum molding pressure is within the above-mentioned range, it can be said that the foam molded product is economically less burdensome.

In general, the higher the water vapor pressure A and/or water vapor pressure B, the higher the internal fusion rate of the resulting foamed molded body tends to be, but once the pressure exceeds a certain value, the internal fusion rate does not change. The higher the water vapor pressure A and/or water vapor pressure B, the more costly it is to pressurize the water vapor. In other words, the lower the water vapor pressure A and/or water vapor pressure B, the more economically advantageous it is. Therefore, the water vapor pressure A and water vapor pressure B when producing a foamed molded body are preferably the lowest pressure within the range in which a foamed molded body with the highest internal fusion rate can be obtained, since the high internal fusion rate of the resulting foamed molded body can be achieved at the same time as economic efficiency, and the water vapor pressure B is preferably the minimum molding pressure. In addition, if the water vapor pressure A and/or water vapor pressure B are excessively high (for example, the molding pressure is 0.25 MPa (gauge pressure) or more), only the surface of the foamed molded body will be preferentially fused, and water vapor will not be able to pass through to the inside of the foamed molded body. As a result, not only does the internal fusion rate decrease, but deformation of the resulting foamed molded product after molding can become significantly large.

The manufacturing method including the above (b1) to (b6) can produce the P3HA foam molded body 100 shown in Figures 3 and 4.

As the manufacturing method including the above (b1) to (b6), the method of filling the molding space of the mold with expanded beads that are not pressurized with air has been described, but the expanded beads may be pressurized when filling the mold. The manufacturing method of the P3HA-based expanded molded article according to one embodiment of the present invention may be, for example, the manufacturing methods (c1) to (c3) below.
(c1) A method of pressurizing expanded beads with an inorganic gas to impregnate the expanded beads with the inorganic gas, imparting a predetermined internal pressure to the expanded beads, filling the expanded beads into a mold, and heating the mold with water vapor;
(c2) A method in which the foamed beads are filled into a mold, the mold is compressed to reduce the volume of the mold by 10% to 75%, and then the mold is heated with steam;
(c3) A method in which the expanded beads are compressed by gas pressure and filled into a mold, and the mold is heated with steam, utilizing the recovery force of the expanded beads.

The inorganic gas in (c1) can be at least one selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc. Among these, air or carbon dioxide is preferred.

The internal pressure of the expanded particles in (c1) is preferably 0.10 MPa (absolute pressure) to 0.30 MPa (absolute pressure), and more preferably 0.15 MPa (absolute pressure) to 0.30 MPa (absolute pressure).

In (c1) above, the temperature inside the container when the inorganic gas is impregnated into the foamed particles is preferably 20°C to 90°C, and more preferably 40°C to 80°C.

The present invention will be described in detail below with reference to 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 (prepared by the inventor, monomer ratio 3HB/3HH = 95/5 (mol%/mol%), melting point 145.0°C)
P3HA-2: P3HB3HH (prepared by the inventor, monomer ratio 3HB/3HH = 89/11 (mol%/mol%), melting point 132.0°C)
P3HA-1 and P3HA-2 were prepared in accordance with the method described in paragraphs [0064] to [0125] of International Publication WO2009/145164.

(Pentaerythritol)
Pentaerythritol (Mitsubishi Chemical's NeuRizer P)
(Fatty acid amide)
Behenamide (Tokyo Chemical Industry Co., Ltd.)
Erucamide (Tokyo Chemical Industry Co., Ltd.)
(Foam Regulator)
Talc (Talc Powder PKS manufactured by Hayashi Kasei Co., Ltd.)
(Foaming Agent)
Carbon dioxide (manufactured by Air Water Inc.)
Nitrogen (manufactured by Air Water Inc.)
(Crosslinking Agent)
Benzoyl peroxide (BPO: NOF Corp. Niper BW)
t-Butylperoxy-2-ethylhexyl monocarbonate (TBEC: Perbutyl E manufactured by NOF Corporation)
(Crosslinking assistant)
Methyl methacrylate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd.)
(Dispersant)
Tricalcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.)
(Dispersing agent)
Sodium alkanesulfonate (Latemul PS, Kao Corporation)
Kaolin (ASP-170 manufactured by BASF)
[Measurement method]
The evaluation methods used in the examples and comparative examples are described below.

(Measurement of Melting Point (Tmp) of Resin Particles)
The melting point (Tmp) of the resin particles was measured using a differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.) The specific operating procedures were as follows (1) to (3): (1) 5 to 6 mg of resin particles were weighed out; (2) the temperature of the resin particles was increased from 10.0°C to 190.0°C at a heating rate of 10.0°C/min to melt the resin particles; (3) the temperature of the highest melting peak in the DSC curve obtained in the above step (2) was taken as the melting point of the resin particles.

(Measurement of Pentaerythritol Content in Expanded Beads)
The pentaerythritol content in the expanded particles was measured by the following methods (1) to (3): (1) 20 mg of the expanded particles was completely dissolved in 0.8 ml of chloroform; (2) 1.6 ml of heavy water containing 1.6 mg of (sodium 3-(trimethylsilyl)propionate-2,2,3,3-d4) was added to the chloroform, and a separation operation was performed to transfer pentaerythritol to the heavy water layer; (3) ¹ The spectra of the pentaerythritol amounts in (a) 1.6 mg to 9.6 mg (1.6 mg, 5.0 mg, 7.0 mg, 9.6 mg) of pentaerythritol standards and (b) the heavy water layer (containing 1.6 mg of (sodium 3-(trimethylsilyl)propionate-2,2,3,3-d4)) extracted in (2) were measured by H-NMR, and the amount of pentaerythritol in the heavy water layer was quantified based on a calibration curve obtained from the measurement results of the pentaerythritol standards, and the pentaerythritol content in the expanded particles was calculated. It should be noted that expanded particles having a crosslinked structure may not be completely dissolved in chloroform. Therefore, the pentaerythritol content in the expanded particles produced under the same conditions as those of each Example and Comparative Example except that no crosslinking agent was used was quantified, and this was taken as the pentaerythritol content in the expanded particles of each Example and Comparative Example (i.e., expanded particles having a crosslinked structure).

(Measurement of DSC Ratio of Expanded Beads)
The DSC ratio of the expanded beads was measured (calculated) using a differential scanning calorimeter (DSC6200, manufactured by Seiko Instruments Inc.). The method for measuring (calculating) the DSC ratio of the expanded beads using a differential scanning calorimeter was as follows (1) to (6): (1) 5 mg to 6 mg of expanded beads were weighed out; (2) The temperature of the expanded beads was raised from 10.0°C to 190.0°C at a heating rate of 10.0°C/min to melt the expanded beads; (3) In the DSC curve obtained in the process (2), a straight line was drawn between the point representing the temperature before the start of melting and the point representing the temperature after the end of melting to prepare a baseline; (4) A straight line passing through the melting peak on the high temperature side or the maximum point between the highest melting peak and the adjacent melting peak was drawn perpendicularly to the X-axis; (5) The heat amount calculated from the high temperature side region surrounded by the baseline, the straight line passing through the maximum point, and the DSC curve was defined as the high temperature side heat of fusion (J/g), and the heat amount calculated from the region surrounded by the baseline and the DSC curve was defined as the total heat of fusion (J/g); (6) The DSC ratio was calculated from the following formula (1):
DSC ratio (%)=(high temperature side heat of fusion/total heat of fusion)×100 (1).

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

(Measurement of density of expanded beads)
The density of the expanded beads was measured by the following methods (1) to (3): (1) a graduated 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 read from the rise in the water level of the ethanol (submersion method) was defined as Vd (cm ³ ); (3) the density of the expanded beads was calculated by the following formula:
Density (g/cm ³ )=Wd/Vd.

(Measurement of internal fusion rate and minimum molding pressure of foamed molded product)
In the following description, the "water vapor pressure during one-sided heating and reverse one-sided heating" is referred to as "water vapor pressure A," and the "water vapor pressure during double-sided heating" is referred to as "water vapor pressure B." The internal fusion rate and molding pressure of the foamed molded body were measured as follows (1) to (3): (1) the water vapor pressure B was changed in increments of 0.01 MPa (gauge pressure) between 0.10 MPa (gauge pressure) and 0.20 MPa (gauge pressure), and the water vapor pressure A was set to 1/2 the water vapor pressure B, and the foamed beads were foamed in a mold at each water vapor pressure B to obtain a foamed molded body; (2) the internal fusion rate was measured for each foamed molded body; (3) the lowest pressure among the water vapor pressures B when a foamed molded body with the highest internal fusion rate was obtained was determined as the minimum molding pressure.

Here, the internal fusion rate was measured as follows (1) to (4): (1) a cut was made with a cutter in the vertical direction (X direction in FIG. 1) on the outer surface of the long side upright wall portion of the foam molded article, the cut having a thickness of 1/15 to 1/6 of the thickness (30 mm); (2) the foam molded article was then broken by hand along the cut; (3) an area of 25 mm (thickness direction) x 90 mm (width) of the obtained fracture surface, excluding the cut portion and including the center in the thickness direction, was visually observed, and the number of all foamed beads present within that area and the number of foamed beads that were broken within that area other than at the particle interface (i.e., foamed beads that were broken within the foamed beads themselves) were counted; (4) the internal fusion rate was calculated based on the following formula (4):
Internal fusion rate (%)=(number of expanded particles broken at other than particle interfaces within the range of 25 mm length (thickness direction)×90 mm width/total number of expanded particles present within the range)×100 (4).

Example 1
(Resin particle manufacturing process)
A twin-screw extruder (TEM-26SX manufactured by Toshiba Machine Co., Ltd.) was used for melt-kneading the P3HA-based composition. 100 parts by weight of P3HA-1, 1.00 parts by weight of pentaerythritol, and 0.10 parts by weight of talc were weighed and dry-blended to prepare a P3HA-based composition. The prepared P3HA-based composition was fed into a twin-screw extruder, and the P3HA-based composition was melt-kneaded at a cylinder set temperature of 130°C to 160°C (melt-kneading process). The melt-kneaded P3HA-based composition at 179°C was discharged from the nozzle of the die attached to the tip of the extruder. The discharged P3HA-based composition was cooled with water at 50°C, and then cut to obtain cylindrical P3HA-based resin particles with a weight of 3.5 mg per particle and a length/diameter of 2.0 (particle molding process). The type and amount of each substance used in the resin particle manufacturing process are shown in the "Resin Blend" column of Table 1.

(Foaming process)
100 parts by weight (2.5 kg) of the P3HA-based resin particles obtained in the above (resin particle manufacturing process), 200 parts by weight of pure water, 2.0 parts by weight of BPO as a crosslinking agent, 1.0 parts by weight of calcium phosphate tribasic as a dispersing agent, and 0.05 parts by weight of sodium alkanesulfonate as a dispersing aid were supplied to a pressure vessel having an internal volume of 10 L. The raw materials in the pressure vessel were stirred. Thereafter, the contents (dispersion) in the pressure vessel were stirred until the release of the dispersion liquid was completed. Nitrogen was introduced into the pressure vessel to perform evacuation, and oxygen in the pressure vessel was removed.

Furthermore, carbon dioxide was supplied as a foaming agent into the pressure vessel to prepare a dispersion (dispersion process). After that, the temperature inside the pressure vessel was raised to a foaming temperature of 129.0°C. Furthermore, carbon dioxide was 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 raising process). Next, the temperature and pressure inside the pressure vessel were held near the foaming temperature and foaming pressure, respectively, for 30 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 under atmospheric pressure through an opening orifice with a diameter of 3.6 mm to obtain P3HA-based expanded particles (release process). The dispersant and the like attached to the surface of the expanded particles were washed with an aqueous sodium hexametaphosphate solution and water, and the expanded particles were dried at 75°C. The types and amounts of each substance used in the foaming process are shown in the "foaming formulation" column of Table 1. The pentaerythritol content, DSC ratio, gel fraction, and density of the obtained expanded particles were measured. The results are shown in Table 1. The length/diameter ratio of the expanded beads was 1.0, and the shape was spherical or nearly spherical.

(Production of P3HA-based foamed molded article)
Using the expanded particles obtained in the above (expansion process), a box-shaped foamed molded article having inner dimensions of long side 400 mm × short side 200 mm × height 100 mm and a bottom and vertical wall thickness of 30 mm was produced by the method described below.

First, a mold consisting of a fixed mold and a movable mold capable of obtaining a box-shaped foam molded product of the above dimensions was mounted on an in-mold foam molding machine (DAISEN KD-345). Then, the movable mold was driven relative to the fixed mold so that a gap of 10 mm (10 mm cracking in the thickness direction of the bottom and the height direction of the vertical wall) was formed between the fixed mold and the movable mold, and a molding space was formed inside. Next, foamed particles that had not been pressurized with air were filled into the molding space of the mold through a filling machine (DAISEN). Next, the movable mold was driven to completely close the mold. The mold was heated with steam on one side for 8 seconds, on the other side for 5 seconds, and on both sides for 15 seconds to obtain a box-shaped foam molded product. The obtained box-shaped foam molded product was removed from the mold and dried at 75°C.

As described in the section (Measurement of internal fusion rate and molding pressure of foamed molded bodies), the water vapor pressure B was changed in increments of 0.01 MPa (gauge pressure) to produce foamed molded bodies at multiple water vapor pressures B, and the internal fusion rate and minimum molding pressure were measured using these foamed molded bodies. The results are shown in Table 1.

Example 2
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the amount of pentaerythritol was 0.05 parts by weight, and the physical properties were measured. The results are shown in Table 1.

Example 3
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the amount of pentaerythritol was 20.00 parts by weight, and the physical properties were measured. The results are shown in Table 1.

Example 4
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the expansion temperature was 130.0° C. and the expansion pressure was 3.5 MPa (gauge pressure), and the physical properties were measured. The results are shown in Table 1.

Example 5
Expanded beads and expanded molded articles were produced in the same manner as in Example 1, except that the expansion temperature was 129.5° C., and the physical properties were measured. The results are shown in Table 1.

Example 6
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the expansion pressure was set to 3.2 MPa (gauge pressure), and the physical properties were measured. The results are shown in Table 1.

Example 7
Except for changing the amount of pentaerythritol to 2.00 parts by weight, the foaming temperature to 128.5° C., and the foaming pressure to 3.2 MPa (gauge pressure), the same method as in Example 1 was used to produce expanded beads and foamed molded articles, and the physical properties were measured. The results are shown in Table 1.

Example 8
In the preparation of the P3HA-based composition, 1.00 parts by weight of behenic acid amide, which is a fatty acid amide, was dry-blended together with P3HA-1, etc., in the same manner as in Example 1, and the expanded beads and expanded molded articles were produced and their physical properties were measured. The results are shown in Table 1.

Example 9
In the preparation of the P3HA-based composition, 0.50 parts by weight of behenamide and 0.50 parts by weight of erucamide, which are fatty acid amides, were dry-blended together with P3HA-1, etc., in the same manner as in Example 1, and the physical properties were measured. The results are shown in Table 1.

Example 10
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the amount of BPO was 1.0 part by weight, and the physical properties were measured. The results are shown in Table 2.

Example 11
The foamed beads and foamed molded article were produced in the same manner as in Example 1, except that in the dispersion step, 0.01 parts by weight of methyl methacrylate as a crosslinking aid was supplied to the pressure vessel together with the P3HA-based resin particles, etc., and the physical properties were measured. The results are shown in Table 2.

Example 12
Expanded beads and expanded molded articles were produced and their physical properties were measured in the same manner as in Example 1, except that 100 parts by weight of P3HA-2 was used instead of P3HA-1 and the expansion temperature was set to 114.0° C. The results are shown in Table 2.

Example 13
The foamed beads and foamed molded articles were produced in the same manner as in Example 1, except that (a) 2.0 parts by weight of TBEC was used instead of BPO as the crosslinking agent, and (b) 0.50 parts by weight of behenamide and 0.50 parts by weight of erucamide, which are fatty acid amides, were dry-blended together with P3HA-1, etc., in the preparation of the P3HA-based composition, and the physical properties were measured. The results are shown in Table 2.

Example 14
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that 1.0 part by weight of kaolin was used as the dispersant instead of calcium phosphate tribasic, and the physical properties were measured. The results are shown in Table 2.

Example 15
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that the blowing agent was changed from carbon dioxide to nitrogen, and the physical properties were measured. The results are shown in Table 2.

Example 16
The expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that no crosslinking agent was used, and the physical properties were measured. The results are shown in Table 2.

Example 17
In the preparation of the P3HA-based composition, 0.10 parts by weight of behenamide and 0.10 parts by weight of erucamide, which are fatty acid amides, were dry-blended together with P3HA-1, etc., in the same manner as in Example 1, and the physical properties were measured. The results are shown in Table 2.

In Tables 1 and 2, "MPa (G)" means "MPa (gauge pressure)."

Comparative Example 1
In the preparation of the P3HA composition, the expanded beads and the expanded molded article were produced in the same manner as in Example 1, except that pentaerythritol was not used, and the physical properties were measured. The results are shown in Table 3.

Comparative Example 2
The expanded beads and expanded molded articles were produced in the same manner as in Example 1, except that the amount of pentaerythritol was 25.00 parts by weight, and the physical properties were measured. The results are shown in Table 3. The expanded beads of Comparative Example 2 had poor extrusion stability using a twin-screw extruder when producing resin beads, and the weight and length/diameter per resin bead varied widely, and the size and shape of the resulting expanded beads also varied widely. In addition, the surface of the expanded beads was sticky, and many of the expanded beads were stuck together. As a result, the expanded beads of Comparative Example 2 had poor mold filling properties when undergoing in-mold expansion molding.

Comparative Example 3
In the preparation of the P3HA-based composition, pentaerythritol was not used, and 1.00 parts by weight of behenic acid amide, which is a fatty acid amide, was dry-blended together with P3HA-1, etc., in the same manner as in Example 1, except that the expanded beads and the expanded molded article were produced, and each physical property was measured. The results are shown in Table 3.

Comparative Example 4
The expanded beads and expanded molded articles were produced and their physical properties were measured in the same manner as in Example 1, except that (a) P3HA-1 was changed to P3HA-2, (b) pentaerythritol was not used in the preparation of the P3HA composition, and (c) the foaming temperature was set to 114.0° C. The results are shown in Table 3.

In Table 3, "MPa (G)" means "MPa (gauge pressure)".
The expanded beads produced in Examples 2 to 17 and Comparative Examples 1, 3, and 4 had a length/diameter ratio of 1.0 and a spherical or nearly spherical shape.

From Tables 1 to 3, the following is clearly evident:
(1) The foamed molded articles of Examples 1 to 17 are foamed molded articles obtained by molding foamed beads containing pentaerythritol in an amount within the range of one embodiment of the present invention;
(2) The foamed molded articles of Examples 1 to 17 have a low minimum molding pressure during production of the foamed molded articles and a high internal fusion rate (good internal fusion property);
(3) Comparing Examples 1 to 17 with Comparative Examples 1, 3, and 4, it was found that when pentaerythritol was not used, the internal fusion rate of the resulting foamed molded article was significantly inferior;
(4) A comparison between Examples 1 to 17 and Comparative Example 2 shows that even when pentaerythritol is used in an amount exceeding the range of the present invention, (a) the granulation of resin particles becomes unstable, resulting in large variation in the size and shape of the expanded particles, (b) many of the expanded particles stick together, and (c) the mold filling property during in-mold foaming becomes poor, resulting in (d) a foamed molded article with a low internal fusion rate (poor internal fusion property) is obtained.

According to one embodiment of the present invention, it is possible to provide P3HA-based foam particles and foam molded products that can provide P3HA-based foam molded products with excellent internal fusion properties at low molding pressure. P3HA-based foam molded products with excellent internal fusion properties are biodegradable and have excellent impact resistance. Therefore, one embodiment of the present invention can be suitably used in fields such as packaging cushioning materials, agricultural product boxes, fish boxes, automotive parts, building materials, and civil engineering materials.

Claims (4)

A poly(3-hydroxyalkanoate) based expanded particle,
poly(3-hydroxyalkanoate) and pentaerythritol,
The content of the pentaerythritol is 0.01% by weight to 4.50% by weight based on 100% by weight of the poly(3-hydroxyalkanoate)-based expanded beads,
The DSC ratio is 0.5% to 40.0%,
Here, the DSC ratio is calculated by the following formula (1):
DSC ratio (%) = (high temperature side heat of fusion/total heat of fusion) x 100 (1),
In the formula (1), the high-temperature side heat of fusion and the total heat of fusion are heat quantities obtained from a DSC curve of the poly(3-hydroxyalkanoate)-based expanded beads. The poly(3-hydroxyalkanoate)-based expanded particles according to claim 1, having a gel fraction of 50% to 80% by weight. The poly(3-hydroxyalkanoate)-based expanded particles according to claim 1 or 2, further comprising 0.01% by weight to 1.50% by weight of a fatty acid amide relative to 100% by weight of the poly(3-hydroxyalkanoate)-based expanded particles. A poly(3-hydroxyalkanoate)-based foamed molded article obtained by molding the poly(3-hydroxyalkanoate)-based foamed beads according to any one of claims 1 to 3.

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