JP2023047823A - Method for producing poly(3-hydroxyalkanoate)-based foamed particle and method for producing poly(3-hydroxyalkanoate)-based foamed molding - Google Patents

Abstract

To provide a method for producing a P3HA-based foamed particle and a method for producing a P3HA-based foamed molding with excellent production efficiency.SOLUTION: A method for producing a poly(3-hydroxyalkanoate)-based foamed particle includes a dispersion step for dispersing poly(3-hydroxyalkanoate) resin particles, an aqueous dispersion medium, an inorganic dispersant, and a foaming agent in a pressure-resistant container, the inorganic dispersant having a specific gravity of 3.5 or more and 5.0 or less.SELECTED DRAWING: None

Description

TECHNICAL FIELD The present invention relates to poly(3-hydroxyalkanoate)-based foamed particles and poly(3-hydroxyalkanoate)-based foamed moldings.

A large amount of petroleum-derived plastics is discarded every year, and the shortage of landfill disposal sites and environmental pollution due to these large amounts of waste have been taken up as serious problems. 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 (a) in environments such as the sea and soil, and (b) in landfills and composts have attracted attention. Biodegradable plastics are used in (a) agricultural, forestry and fishery materials used in the environment, and (b) food containers, packaging materials, sanitary goods, garbage bags, etc. that are difficult to collect and reuse after use. Development is underway with the aim of wide-ranging applications. Furthermore, foams made of biodegradable plastics are expected to be used in cushioning materials for packaging, boxes for agricultural products, boxes for fish, automobile members, building materials, civil engineering materials, and the like.

Among the biodegradable plastics, poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as "P3HA") is attracting attention as a plant-based plastic from the viewpoint of excellent biodegradability and carbon neutrality. there is

Development of the above-mentioned biodegradable plastics for use in molded articles is under consideration. For example, Patent Literature 1 discloses expanded beads obtained using biodegradable P3HA, and a technique for obtaining a foamed article by subjecting the expanded beads to in-mold foam molding.

WO2019/146555

However, in the above-described prior art, there is room for improvement in production efficiency of P3HA-based expanded beads.

In view of the circumstances as described above, an object of an embodiment of the present invention is to provide a method for producing expanded P3HA beads and a method for producing a P3HA expanded molded article with excellent production efficiency.

The inventors of the present invention have completed the present invention as a result of intensive studies to solve the above problems.

That is, one embodiment of the present invention includes the following configurations.
[1] A method for producing poly(3-hydroxyalkanoate)-based expanded beads, comprising:
A dispersing step of dispersing poly(3-hydroxyalkanoate) resin particles, an aqueous dispersion medium, an inorganic dispersant, and a foaming agent in a pressure vessel,
A method for producing poly(3-hydroxyalkanoate) expanded particles, wherein the inorganic dispersant has a specific gravity of 3.5 or more and 5.0 or less.

[2] The method for producing poly(3-hydroxyalkanoate)-based expanded particles according to [1], wherein the inorganic dispersant is at least one selected from the group consisting of aluminum oxide, titanium oxide, and barium sulfate. .

[3] The method for producing poly(3-hydroxyalkanoate)-based expanded beads according to [1], wherein the inorganic dispersant is aluminum oxide.

[4] The poly(3-hydroxyalkanoate) according to any one of [1] to [3], wherein the inorganic dispersant has a hydrogen ion concentration (pH) of less than 7.5. A method for producing a system foamed particle.

[5] In the dispersing step, the amount of water used is 130 parts by weight or more and less than 200 parts by weight with respect to 100 parts by weight of the poly(3-hydroxyalkanoate) resin particles [1] to [ 4].

[6] a step of producing poly(3-hydroxyalkanoate)-based expanded beads by the production method according to any one of [1] to [5];
A method for producing a poly(3-hydroxyalkanoate)-based expanded molded article, comprising a step of heating and molding the expanded particles in a mold.

According to one embodiment of the present invention, there is an effect that it is possible to provide a method for producing P3HA-based expanded beads and a method for producing a P3HA-based expanded molded article, which are excellent in production efficiency. In addition, the decrease in the gel fraction of the P3HA-based expanded beads is suppressed, and the desired P3HA-based expanded beads can be easily obtained.

FIG. 2 is a diagram showing a DSC curve of P3HA-based resin particles and melting points and the like measured therefrom; FIG. 4 is a diagram showing a DSC curve of P3HA-based expanded beads and the heat of fusion on the high temperature side measured therefrom;

An embodiment of the invention will be described below, but the invention is not limited thereto. The present invention is not limited to each configuration described below, and various modifications are possible within the scope of the claims. Further, embodiments or examples obtained by combining 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. In addition, all the scientific literatures and patent documents described in this specification are used as references in this specification. In addition, unless otherwise specified in this specification, "A to B" representing a numerical range means "A or more (including A and greater than A) and B or less (including B and less than B)".

[1. Technical idea of the present invention]
As a method for producing P3HA-based expanded beads, P3HA-based resin particles, water, an inorganic dispersant, and a foaming agent are dispersed in a pressure vessel, and then the dispersion is discharged from the pressure vessel to obtain expanded particles. A method is disclosed, and a specific inorganic dispersant includes a technique using calcium phosphate. However, according to this production method, the P3HA-based resin particles may remain in the pressure container even after the dispersion has been discharged from the pressure container, and there is a problem that the production efficiency is deteriorated. There is room.

As a method for reducing the amount of P3HA-based resin particles remaining in the pressure vessel, there is a method of increasing the amount of calcium phosphate or increasing the amount of water. , the problem of contamination of the mold with calcium phosphate tends to occur during in-mold foam molding. Moreover, since the amount of calcium phosphate in the waste water also increases, there is also the problem that the burden of waste water treatment increases. In the latter case, there is a problem that the amount of P3HA-based expanded particles produced per batch decreases and the amount of wastewater increases.

In view of the circumstances as described above, the present inventors conducted intensive studies for the purpose of providing a method for producing P3HA-based expanded beads and a method for producing a P3HA-based expanded molded article, which are excellent in production efficiency.

As a result of intensive studies, the present inventors have independently found the following knowledge and completed the present invention: P3HA-based resin particles, an aqueous dispersion medium, an inorganic dispersant, and a foaming agent are dispersed in a pressure vessel. In the method for producing expanded P3HA particles, the method for producing expanded particles of P3HA has excellent production efficiency by using an inorganic dispersant having a specific gravity of 3.5 or more and 5.0 or less. To provide a method for producing a foam molded article.

[2. Method for Producing Poly(3-Hydroxyalkanoate) Expanded Particles]
A method for producing poly(3-hydroxyalkanoate)-based expanded beads according to one embodiment of the present invention includes poly(3-hydroxyalkanoate)-based resin particles, water, an inorganic dispersant, and a foaming agent in a pressure vessel. A dispersing step of dispersing is included, and the specific gravity of the inorganic dispersant is 3.5 or more and 5.0 or less.

In the present specification, "poly(3-hydroxyalkanoate)-based resin particles" are sometimes referred to as "resin particles", and "poly(3-hydroxyalkanoate) (P3HA)-based expanded particles" are referred to as "expanded particles". "Method for producing poly(3-hydroxyalkanoate) (P3HA) expanded particles" may be called "manufacturing method", and "poly(3-hydroxy alkanoate) (P3HA)-based foamed beads" may be referred to as "this production method".

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

Since the present production method has the above-described structure, it has the advantage of being able to efficiently produce P3HA-based expanded beads.

<Poly(3-hydroxyalkanoate) resin particles>
A resin particle according to one embodiment of the present invention comprises a poly(3-hydroxyalkanoate) resin composition. In this specification, "poly(3-hydroxyalkanoate) (P3HA) resin composition" may be referred to as "resin composition".

First, each component contained in the resin composition, that is, the resin particles will be described.

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

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

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

P3HA preferably contains 50 mol% or more, more preferably 70 mol% or more, and 80 mol% of 3HA units (especially repeating units of general formula (1)) in 100 mol% of all repeating units of P3HA. It is more preferable to include the above. In addition, the repeating unit (monomer unit) may be 3HA unit only, or may contain a repeating unit derived from a monomer other than 3HA (for example, 4-hydroxyalkanoate unit, etc.) in addition to 3HA unit. You can stay.

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 propylene. Therefore, the P3HA according to one embodiment of the invention preferably comprises 3-hydroxybutyrate units. In this specification, "3-hydroxybutyrate" may be referred to as "3HB".

P3HA preferably contains 3HB units (monomer units) in an amount of 80 mol% or more, more preferably 85 mol% or more, based on 100 mol% of all repeating units of P3HA. P3HA is particularly preferably a polymer containing 3HB units and all 3HBs are (R)-3HB (polymers produced by microorganisms).

When P3HA contains two or more kinds of repeating units, the monomer from which repeating units other than the repeating unit with the highest content are derived is called a comonomer. In this specification, the "repeating unit derived from a comonomer" may be referred to as a "comonomer unit".

Although the comonomer is not particularly limited, 3-hydroxyhexanoate (hereinafter sometimes referred to as 3HH) or 4-hydroxybutyrate (hereinafter sometimes referred to as 4HB) is preferable.

Specific examples of P3HA include poly(3-hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxybutyrate), rate) (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 (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"), and the like. In particular, poly(hydroxybutyrate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate), poly(3-hydroxybutyrate-co-3), from the viewpoint of workability and physical properties of foamed molded products. -hydroxyvalerate-co-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate), or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) is preferred. In one embodiment of the present invention, as the P3HA described above, one type may be used alone, or two or more types may be used in combination.

P3HA preferably has a 3HB unit as an essential repeating unit (structural unit) and also has a comonomer unit. That is, P3HA is preferably a copolymer having 3HB units and comonomer units. The case where P3HA has 3HB units and comonomer units will be described. In this case, the ratio of 3HB units and comonomer units in 100 mol% of all repeating units in P3HA (3HB units/comonomer units) is 99/1 (mol%/mol%) to 80/20 (mol%/mol %) is preferable, 97/3 (mol%/mol%) to 80/20 (mol%/mol%) is more preferable, and 95/5 (mol%/mol%) to 85/15 (mol%/mol% ) is more preferred. If the ratio of the comonomer unit to 100 mol% of the total repeating units of P3HA is 1 mol% or more, the temperature range in which P3HA can be melt-kneaded and the temperature range for thermal decomposition are sufficiently separated, so that the obtained expanded particles can be processed. It has the advantage of being highly flexible. On the other hand, when the ratio of comonomer units to 100 mol % of all repeating units of P3HA is 20 mol % or less, crystallization of the P3HA-based composition is rapid 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 WO2013/147139.

The melting point of P3HA is not particularly limited, but is preferably 110.0°C to 165.0°C, 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 in the resulting foamed molded product upon heating. No fear.

Here, the melting point of P3HA is measured by a differential scanning calorimeter method (hereinafter referred to as "DSC method"). The specific operating procedure is as follows: (1) Weigh 5 mg to 6 mg of P3HA; (2) Increase the temperature of P3HA from 10.0° C. to 190.0° C. at a rate of 10.0° C./min. (3) The temperature of the highest melting peak in the DSC curve of P3HA obtained in the process (2) above 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 concern that the foamed beads obtained will have a low closed cell content. On the other hand, if the weight-average molecular weight is 2,000,000 or less, the load on the machine during melt-kneading the P3HA-based composition is reduced, resulting in good productivity. The weight average molecular weight of P3HA can be measured from the polystyrene equivalent molecular weight distribution using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. As a column in the gel permeation chromatography, a known column suitable for measuring 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 by chemical synthesis or a production method by microorganisms. Among them, the production method using microorganisms is preferable. A known method can be applied to the method for producing P3HA using microorganisms.

Specific examples of 3HB and other hydroxyalkanoate-producing bacteria include Aeromonas caviae, which is a P3HB3HV and P3HB3HH-producing bacterium, and Alcaligenes eutrophus, which is a P3HB4HB-producing bacterium. be done. In particular, with regard to P3HB3HH, Alcaligenes eutrophus AC32 (FERM BP-6038) strain (Alcaligenes eutrophus AC32, FERM BP-6038), in which the productivity of P3HB3HH is improved by introducing a P3HA synthase group gene (T. Fukui, Y. Doi, J. Med. Bateriol., 179, p4821-4830 (1997)) and the like are more preferred. In the method for producing P3HA, microbial cells obtained by culturing microorganisms such as Alcaligenes eutrophus AC32 strain under appropriate conditions to accumulate P3HB3HH in the cells are preferably used. In addition to the above-mentioned copolymer-producing bacteria, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may be used according to the P3HA to be produced. In addition, various culture conditions, including the type of substrate, may be optimized according to the P3HA to be produced with respect to the culture conditions of microorganisms (bacteria).

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 resin particles is not particularly limited, but is preferably 90% by weight or more, preferably 95% by weight, based on 100% by weight of the resin particles, since the obtained expanded beads and expanded molded articles are excellent in biodegradability. The above is more preferable.

The resin particles may further contain resin components other than P3HA (sometimes referred to as "other resin components"). Other resin components include, for example, (a) aliphatic polyesters such as polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone, or (b) fatty aromatic polyesters, and the like. Together with P3HA, one of these other resin components may be used alone, or two or more may be used in combination.

The content of other resin components in the resin particles is not particularly limited, but is preferably 10% by weight or less, more preferably 5% by weight or less, based on 100% by weight of the resin particles. The resin particles may not contain other resin components.

(Additive)
The resin particles further contain additives such as crystal nucleating agents, cell control agents, lubricants, water-soluble polymers, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, cross-linking agents, antioxidants, and ultraviolet absorbers. Agents, colorants, inorganic fillers, organic fillers, hydrolysis inhibitors and the like can be used depending on the purpose. Among these additives, biodegradable additives are particularly preferred.

Crystal nucleating agents include, for example, pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. One type of these crystal nucleating agents may be used alone, or two or more types may be mixed and used. Moreover, when two or more kinds of crystal nucleating agents are mixed and used, the mixing ratio may be appropriately adjusted according to the purpose.

The content of the crystal nucleating agent in the resin particles is preferably 5.0 parts by weight or less, more preferably 3.0 parts by weight or less, and even more preferably 1.5 parts by weight or less with respect to 100 parts by weight of P3HA. When the content of the crystal nucleating agent in the resin particles is 5.0 parts by weight or less with respect to 100 parts by weight of P3HA, there is an advantage that there is no risk of hindering the fusion of the foamed particles obtained by foaming the resin particles. Although the lower limit of the content of the crystal nucleating agent in the resin particles is not particularly limited, it can be, for example, 0.1 parts by weight or more with respect to 100 parts by weight of the resin particles.

Examples of cell regulators include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, bentonite and the like. Among these cell control agents, talc is preferable because it is particularly excellent in dispersibility in P3HA. Moreover, one type of these cell control agents may be used alone, or two or more types may be mixed and used. In addition, when two or more types of cell control agents are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The content of the cell control agent in the resin particles is not particularly limited, but is preferably 0.01 to 1.00 parts by weight, more preferably 0.03 to 0.50 parts by weight, relative to 100 parts by weight of P3HA. Preferably, 0.05 to 0.30 parts by weight is more preferable.

Examples of lubricants include behenic acid amide, oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, N-stearylbehenic acid amide, N-stearyl erucic acid amide, ethylene bis stearic acid amide, ethylene bis oleic acid amide, ethylenebiserucamide, ethylenebislaurylamide, ethylenebiscapricamide, p-phenylenebisstearicamide, polycondensates of ethylenediamine, stearic acid and sebacic acid. Among these lubricants, behenic acid amide and/or erucic acid amide are preferable because they are particularly effective in lubricating P3HA. One type of these lubricants may be used alone, or two or more types may be mixed and used. Moreover, when two or more types of lubricants are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The content of the lubricant in the resin particles is not particularly limited, but is preferably 0.01 to 5.00 parts by weight, more preferably 0.05 to 3.00 parts by weight, based on 100 parts by weight of P3HA. More preferably 0.10 to 1.50 parts by weight.

Examples of water-soluble polymers include polyethylene glycol, polypropylene glycol, polybutylene glycol, and copolymers thereof.

When a water-soluble polymer is added to the resin particles, the content thereof is 0.01 to 1.50 parts by weight, and 0.02 to 1.50 parts by weight with respect to 100 parts by weight of P3HA. preferably 0.02 to 1.00 parts by weight, even more preferably 0.50 to 1.00 parts by weight.

When the resin particles contain (a) 0.01 parts by weight or more of the water-soluble polymer with respect to 100 parts by weight of P3HA, the foamed particles provide a foamed molded article with even better internal fusion bondability at a low molding pressure. (b) When the content is 1.50 parts by weight or less, there is no fear that a large amount of the water-soluble polymer will seep out (bleed) onto the surface of the expanded beads.

Examples of plasticizers include glycerin ester compounds such as glycerin diacetomonolaurate, citrate compounds such as acetyl tributyl citrate, sebacate compounds such as dibutyl sebacate, adipate compounds, and polyethers. Ester-based compounds, benzoate-based compounds, phthalate-based compounds, isosorbide ester-based compounds, polycaprolactone-based compounds, dibasic acid ester-based compounds such as benzylmethyldiethylene glycol adipate, and the like. Among these, glycerin ester-based compounds, citric acid ester-based compounds, sebacate-based compounds, and dibasic acid ester-based compounds are preferred because of their particularly excellent plasticizing effect on P3HA. One type of these plasticizers may be used alone, or two or more types may be mixed and used. Moreover, when mixing and using two or more types of plasticizers, you may adjust a mixing ratio suitably according to the objective.

The content of the plasticizer in the resin particles is not particularly limited, but is preferably 1 part by weight to 20 parts by weight, more preferably 2 parts by weight to 15 parts by weight, and 3 parts by weight to 10 parts by weight with respect to 100 parts by weight of P3HA. is more preferred.

<Method for producing poly(3-hydroxyalkanoate) resin particles>
Next, a method for producing resin particles will be described. A method for producing the resin particles is not particularly limited, and known methods can be used. The method for producing resin particles can be said to be a method of molding a resin composition into a shape that can be easily used for foaming, and can also be said to be a method of preparing resin particles. This production method may include a method for producing resin particles as one step before the dispersing step. In other words, the production method may include a resin particle preparation step before the dispersion step.

(Resin particle preparation step)
The resin particle preparation step is a step of preparing P3HA-based resin particles containing P3HA and, if necessary, additives.

A specific aspect of the resin particle preparation step is not particularly limited. The resin particle preparation step includes (a) a melt-kneading step of melt-kneading a resin composition containing P3HA and, if necessary, additives;
(b) It is preferable to include a particle molding step of molding the melt-kneaded resin composition into a shape that can be easily used for foaming.

The aspect 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 (b1) and (b2):
(b1) P3HA and, if necessary, additives are mixed or blended in a mixing device or the like to prepare a resin composition. Thereafter, a method of supplying the resin composition to a melt-kneading device and melt-kneading;
(b2) A method in which P3HA and, if necessary, additives are supplied to a melt-kneading device, a resin composition is prepared (completed) in the melt-kneading device, and the resin composition is melt-kneaded.

In the above method (b1), the order of mixing or blending (dry blending) P3HA and, if necessary, additives is not particularly limited. In the method (b2), the order of supplying P3HA and, if necessary, additives to the melt-kneading apparatus is not particularly limited.

In the method (b1), the mixing device is not particularly limited, and includes a ribbon blender, a flash blender, a tumbler mixer, a super mixer and the like.

In the above methods (b1) and (b2), the melt-kneading device is not particularly limited, and examples thereof include extruders, kneaders, Banbury mixers, and rolls. As the melt-kneading device, an extruder is preferable, and a single-screw extruder or a twin-screw extruder is more preferable, because of its excellent productivity and convenience.

In the method (b1), the amount of the additive used for mixing or blending is the content of the additive in the resulting resin particles. In the method (b2), the amount of the additive supplied to the melt-kneading device is the content of the additive in the obtained resin particles. Therefore, with regard to the amount of the additive to be used and the amount to be supplied, the description in the above section (Additive) is used. It is not necessary to use all the additives used in this production method in the resin particle preparation step. In other words, all or part of the additives used in the production method (for example, a cross-linking agent, a plasticizer, etc.) are not used in the resin particle preparation step, that is, without being contained in the resin particles, and the subsequent dispersion step may be added to the dispersion at .

In the melt-kneading step, the temperature at which the resin composition is melt-kneaded depends on the physical properties of P3HA (melting point, weight-average molecular weight, etc.), the type of additives used, and the like, and cannot be categorically defined. Regarding the temperature when 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 composition temperature) is 150°C to 200°C. , more preferably 160°C to 195°C, even more preferably 170°C to 190°C. When the composition temperature is 150° C. or higher, there is no risk of insufficient melt-kneading of the resin composition. On the other hand, when the composition temperature is 200° C. or less, there is no risk of thermal decomposition of P3HA.

The form of the particle forming step is not particularly limited as long as the melt-kneaded resin composition can be formed 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 formed into a desired shape in the particle forming step. Specifically, the melt-kneaded resin composition is discharged from a nozzle of a die provided in the melt-kneading device, and the resin composition is cut by a cutting device at the same time as or after the discharge to obtain a desired shape. can be molded into The shape of the resin particles to be obtained is not particularly limited, but cylindrical, cylindric, spherical, cubic, cuboid, and the like are preferable because they are easily used for foaming.

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

In the particle molding step, when cooling the resin composition discharged from the nozzle of the die, the temperature exhibited by the cooled resin composition (hereinafter sometimes referred to as cooling temperature) is not particularly limited. The cooling temperature is preferably 20°C to 80°C, more preferably 30°C to 70°C, even more preferably 40°C to 60°C. According to this configuration, the crystallization of the melt-kneaded resin composition is sufficiently rapid, so there is an advantage that the productivity of the resin particles is improved.

(Physical properties of poly(3-hydroxyalkanoate) resin particles)
(Melting point of resin particles)
The melting point (hereinafter sometimes referred to as "Tmp") of the resin particles is not particularly limited, but is preferably 110.0°C to 165.0°C, more preferably 120.0°C to 155.0°C. If the melting point of the resin particles is 110.0° C. or higher, it is possible to suppress dimensional changes due to heating during molding of the obtained expanded beads. On the other hand, if the melting point of the resin particles is 165.0° C. or less, there is no fear of hydrolysis of P3HA during foaming of the resin particles. Components other than P3HA contained in the resin particles (for example, additives) hardly affect 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 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 "DSC method"). The specific operating procedure is as follows: (1) 5 mg to 6 mg of resin particles are weighed out; (2) the temperature of the resin particles is increased from 10.0° C. to 190° C. at a rate of 10.0° C./min. (3) As shown in FIG. 1, the temperature of the highest melting peak of the DSC curve of the resin particles obtained in the process of (2) above is taken as the temperature of the resin particles. can be obtained as the melting point of

FIG. 1 is a diagram showing the DSC curve of P3HA resin particles and the melting point and the like measured therefrom. Since the DSC curve shown in FIG. 1 has one melting peak, the temperature of the melting peak is the melting point of the resin particles.

(Weight per resin particle)
The weight per resin particle is not particularly limited, but is preferably 0.3 mg to 10.0 mg, more preferably 0.5 mg to 5.0 mg. If the weight per resin particle is 0.3 mg or more, the resin particles can be stably produced with high productivity. On the other hand, if the weight per resin bead is 10.0 mg or less, the expanded bead obtained from the resin bead can easily provide a thin-walled expansion molded article.

(Shape of resin particles)
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 2.0 to 2.0. .7 is more preferred. If the length/diameter ratio of the resin particles is 0.5 to 3.0, the shape of the resulting expanded particles is not flat, but tends to be spherical or approximately spherical. Spherical or approximately spherical foamed particles can be easily filled into a molding space of a mold of a molding machine, and can provide a foamed molded product with excellent surface beauty. Here, the length of a resin particle is intended to be the maximum value of the distance between two cut surfaces appearing (occurring) in a resin particle when the resin particle is cut in the manufacturing process of the resin particle. Next, assuming that 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. A line segment obtained by cutting the straight line y at the cross section x is called a line segment y, and a line segment obtained by cutting the straight line z at the cross section x is called a line segment z. The diameter of the resin particles is intended to be the average value of the length of the line segment y and the length of the line segment z.

<Method for Producing Poly(3-Hydroxyalkanoate) Expanded Particles>
Next, the steps of the present method for producing P3HA-based expanded beads will be described.

(Dispersion process)
The dispersing step can also be said to be a step of preparing a dispersion in which the P3HA-based resin particles, the inorganic dispersant, and the foaming agent are dispersed in an aqueous dispersion medium in a pressure vessel. If necessary, a cross-linking agent such as an organic peroxide, a cross-linking aid, a plasticizer, or a dispersing aid may be added to form a dispersion. In the dispersion, (a) a cross-linking agent such as an organic peroxide and a cross-linking aid are consumed by the reaction with the P3HA in the resin particles and may not be present; The agent may not be present in a state of being impregnated and dispersed in the resin particles.

Although the pressure-resistant container is not particularly limited, it is preferably a pressure-resistant container that can withstand the later-described foaming temperature and foaming pressure. Moreover, it is more preferable that the container is a pressure-resistant container having a stirring means so that the dispersion can be easily dispersed. The stirring means is not particularly limited, and includes a general stirring blade, a stirrer (pulsator) attached to the bottom of the pressure vessel, and the like.

The aqueous dispersion medium is not particularly limited as long as it can uniformly disperse resin particles, an inorganic dispersant, a foaming agent, and the like. As the aqueous dispersion medium, for example, tap water and/or industrial water can be used. From the viewpoint of stable production of foamed particles, water-based dispersion media include RO water (water purified by reverse osmosis membrane method), distilled water, deionized water (water purified by ion exchange resin), and the like. It is preferable to use pure water, ultrapure water, or the like.

The amount of the aqueous dispersion medium used is not particularly limited, but is preferably 100 parts by weight to 1000 parts by weight, more preferably 120 parts by weight to 500 parts by weight, and 130 parts by weight or more and 200 parts by weight with respect to 100 parts by weight of the resin particles. Less than is preferable, 130 to 190 weight parts is more preferable, and 130 to 180 weight parts is most preferable. According to this production method using a specific inorganic dispersant, it is possible to produce with the amount of the aqueous dispersion medium used being 130 parts by weight or more and less than 200 parts by weight, and the variation in the expansion ratio of the P3HA-based expanded particles does not deteriorate. Good expanded beads can be obtained, and the amount of wastewater can be easily reduced.

In this production method, an inorganic dispersant having a specific gravity of 3.5 to 5.0 is used. The use of an inorganic dispersant has the advantage of suppressing coalescence (sometimes referred to as blocking) between resin particles and stably producing expanded beads. It is easy to reduce the amount of resin particles remaining in the pressure vessel after the release process (the process of releasing one end of the pressure vessel and releasing the dispersion liquid in the pressure vessel), and it is possible to improve the production efficiency of expanded beads. becomes. From such a viewpoint, the specific gravity is more preferably 3.6 to 4.9, more preferably 3.7 to 4.8, and most preferably 3.8 to 4.6. The specific gravity is obtained by dividing the density of the inorganic dispersant by the density of water (the density of the inorganic dispersant/the density of the water). Density) can be confirmed by referring to the catalog of the inorganic dispersant maker or by asking the inorganic dispersant maker.

In order to prepare the dispersion liquid, the inside of the pressure vessel can be stirred and mixed with a stirring blade or the like. It is easy to lead to reduction of waste and reduction of environmental load.

The inorganic dispersant as described above is not particularly limited, but examples thereof include inorganic dispersants such as aluminum oxide, titanium oxide, barium sulfate, magnesium oxide, molybdenum oxide, strontium carbonate, barium carbonate, and strontium titanate. From the viewpoint of production efficiency, aluminum oxide, titanium oxide and barium sulfate are more preferable, and aluminum oxide is most preferable. One type of these inorganic dispersants may be used alone, or two or more types may be mixed and used. Moreover, when mixing and using two or more types of inorganic dispersants, the mixing ratio may be appropriately adjusted according to the purpose.

Although the hydrogen ion concentration (pH) of the inorganic dispersant is not particularly limited, it is preferably less than 7.5. When an inorganic dispersant having a hydrogen ion concentration (pH) of less than 7.5 is used, a cross-linking agent such as an organic peroxide is used in combination to reduce the gel fraction of the P3HA-based expanded particles obtained by cross-linking. It also has the effect of suppressing the decrease and making it easier to obtain the desired P3HA-based expanded beads. From such a viewpoint, the hydrogen ion concentration (pH) of the inorganic dispersant is preferably 3.0 or more and less than 7.5, more preferably 4.0 or more and less than 7.5, and most preferably 4.0 or more and 7.0 or less. preferable. The hydrogen ion concentration of the inorganic dispersant refers to the hydrogen ion concentration when the inorganic dispersant is mixed with pure water to form a 4% by weight suspension.

The amount of the inorganic dispersant used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight, more preferably 0.3 to 2.5 parts by weight, relative to 100 parts by weight of the resin particles. , more preferably 0.5 to 2.0 parts by weight, most preferably 0.7 to 1.5 parts by weight.

Examples of foaming agents include inorganic gases such as nitrogen, carbon dioxide, and air; saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane; dimethyl ether, diethyl ether, and methyl ethyl ether. ethers such as cyclomethane; halogenated hydrocarbons such as monochloromethane, dichloromethane and dichlorodifluoroethane; and water. As the foaming agent, at least one selected from the group consisting of inorganic gases, saturated hydrocarbons having 3 to 5 carbon atoms, ethers, halogenated hydrocarbons and water can be used. Among them, it is preferable to use nitrogen, carbon dioxide or water as the blowing agent, and it is particularly preferable to use carbon dioxide, from the viewpoint of environmental load and foaming power. One type of these foaming agents may be used alone, or two or more types may be mixed and used. Moreover, when mixing and using two or more types of foaming agents, you may adjust a mixing ratio suitably according to the objective.

The amount of the foaming agent used is not particularly limited, but is preferably 2 parts by weight to 1000 parts by weight, more preferably 5 parts by weight to 500 parts by weight, and more preferably 10 parts by weight to 300 parts by weight with respect to 100 parts by weight of the resin particles. More preferred. When the amount of the foaming agent used is 2 parts by weight or more with respect to 100 parts by weight of the resin particles, expanded beads having a suitable density can be obtained. On the other hand, when the amount of the foaming agent used is 1000 parts by weight or less with respect to 100 parts by weight of the resin particles, an effect corresponding to the amount of the foaming agent used can be obtained, and no economic waste occurs.

In this production method, the cross-linking agent is not particularly limited as long as it can cross-link P3HA, but it is preferable to use an organic peroxide. In other words, the P3HA-based foamed particles are preferably crosslinked with an organic peroxide. The organic peroxide may be used in (a) the resin particle preparation step, (b) the dispersion step, or (c) the resin particle preparation step and the dispersion step. 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 preparation step, and (b) the resin particles and the organic The peroxide may be dispersed in an aqueous dispersion medium, and (c) the organic peroxide and P3HA are melt-kneaded, and the resin particles and the organic peroxide are dispersed in the aqueous dispersion medium. good too. In the dispersing step, the resin particles produced in the resin particle preparation step and the organic peroxide are dispersed in an aqueous dispersion medium, so that the resin particles can be impregnated and reacted with the organic peroxide. For these reasons, an organic peroxide is preferred as the cross-linking agent in the present method for producing expanded beads. When an organic peroxide is used as a cross-linking agent, a cross-linked structure is formed by directly bonding the molecular chains of P3HA (without passing through a structure derived from the cross-linking agent). In the dispersion liquid, the organic peroxide and the cross-linking aid as the cross-linking agent are consumed by the reaction with the P3HA in the resin particles and may not be present.

The organic peroxide used in this production method can function as a cross-linking agent for the resin particles, more specifically the P3HA in the resin particles. By using an organic peroxide in this production method, P3HA in the obtained expanded particles becomes P3HA having a crosslinked structure. That is, it is possible to obtain expanded P3HA beads having an excellent gel fraction. That is, by using an organic peroxide in the production method of the present invention, (a) when molding a foamed molded article, the molding temperature range of the foamed particles that can provide a good quality foamed molded article is widened, and productivity is improved. In addition, there is the advantage that (b) a foam molded article having excellent internal fusion bondability can be obtained with a low molding pressure. Since the cross-linking reaction of P3HA in the resin particles also proceeds in the foaming process, the foaming process can also be said to be a cross-linking process.

The organic peroxide used as a cross-linking agent is preferably an organic peroxide having a 1-hour half-life temperature of 90° C. to 160° C., and a 1-hour half-life temperature of 110° C., depending on the type of P3HA used. Organic peroxides of ~160°C are more preferred, organic peroxides of 110°C to 125°C are more preferred, and organic peroxides of 114°C to 124°C are particularly preferred. Specific examples of such organic peroxides include benzoyl peroxide (BPO, 1-hour half-life temperature: 92° C.), t-butylperoxy-2-ethylhexyl carbonate (TBEC, 1-hour half-life temperature: 121 ° C.), t-butyl peroxyisopropyl carbonate (TBIC, 1-hour half-life temperature: 118° C.), t-amylperoxy-2-ethylhexyl carbonate (TAEC, 1-hour half-life temperature: 117° C.), t-amyl per Oxyisopropyl carbonate (TAIC, 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 peroxy isononanoate (1-hour half-life temperature: 123 ° C.), t-butyl peroxyacetate (1-hour half-life temperature: 123 ° C.), t-butyl peroxy di Benzoate (1-hour half-life temperature: 125 ° C.), t-amyl peroxyisobutyrate (1-hour half-life temperature: 93 ° C.), t-amyl peroxy-2-ethylhexanoate (1-hour half-life temperature: 92 ° C.), t-amyl peroxyisononanoate (1 hour half-life temperature: 114 ° C.), t-amyl peroxyacetate (1 hour half-life temperature: 120 ° C.), t-amyl peroxybenzoate (1 hour half-life 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.) and the like. The use of an organic peroxide having a 1-hour half-life temperature of 90° C. or higher has the advantage that it tends to give foamed beads with a desired gel fraction. On the other hand, the use of an organic peroxide having a 1-hour half-life temperature of 160° C. or less has the advantage that there is no risk of unreacted cross-linking agents remaining in the final product.

The amount of the cross-linking 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, based on 100 parts by weight of the resin particles. More preferably 0.5 to 2.5 parts by weight. When the amount of the cross-linking agent used is 0.1 part by weight or more relative to 100 parts by weight of the resin particles, (a) the obtained expanded beads can be sufficiently cross-linked, and (b) the obtained expanded beads can be independent. It is possible to obtain a foamed molded article having a high void content, good surface beauty and a small molding shrinkage. On the other hand, when the amount of the cross-linking agent used is 5.0 parts by weight or less with respect to 100 parts by weight of the resin particles, an effect corresponding to the amount of the cross-linking agent added can be obtained, so there is no possibility of causing economical waste. . The amount of the cross-linking agent used has a positive correlation with the gel fraction of the expanded beads, and greatly affects the gel fraction of the expanded beads. Therefore, it is desirable to strictly set the amount of the cross-linking agent to be used in consideration of the gel fraction of the obtained expanded beads. In some cases, the resin particles used in the dispersion step already contain a cross-linking agent. In that case, the amount of the cross-linking agent already contained in the resin particles before the dispersion step and the amount of the cross-linking agent used in the dispersion step. It is preferable that the total amount of and satisfies the above range. The amount of the organic peroxide used has a positive correlation with the gel fraction of the foamed beads, and greatly affects the gel fraction of the foamed beads. Therefore, it is desirable to strictly set the amount of the organic peroxide to be used in consideration of the gel fraction of the expanded beads to be obtained.

In this production method, a cross-linking aid may be used in order to improve the cross-linking efficiency of P3HA. Cross-linking aids include, for example, compounds having at least one unsaturated bond in the molecule. Among these compounds, allyl esters, acrylic acid esters, methacrylic acid esters, divinyl compounds, and the like are particularly preferable as the cross-linking aid. One type of these cross-linking aids may be used alone, or two or more types may be mixed and used. Moreover, when mixing and using two or more types of cross-linking aids, the mixing ratio may be appropriately adjusted depending on 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, based on 100 parts by weight of the resin particles. More preferably 0.05 to 1.00 parts by weight. When the amount of the cross-linking aid used is 0.01 part by weight or more with respect to 100 parts by weight of the resin particles, it exhibits a sufficient effect as the cross-linking aid.

In the dispersing step, when the resin particles are impregnated and reacted with an organic peroxide cross-linking agent and/or a cross-linking aid, the oxygen concentration in the container and the dissolved oxygen amount in the dispersion are adjusted to increase the cross-linking efficiency of P3HA. is preferred to be low. Methods for lowering the oxygen concentration in the container and the dissolved oxygen content in the dispersion include replacing the gas in the container and the gas dissolved in the dispersion with an inorganic gas such as carbon dioxide and nitrogen; Evacuate the gas inside.

In this production method, a dispersing aid may be used in order to improve the effect of suppressing coalescence between resin particles. Examples of dispersion aids include anionic surfactants such as sodium alkanesulfonate, sodium alkylbenzenesulfonate, and sodium α-olefinsulfonate. One type of these dispersing aids may be used alone, or two or more types may be mixed and used. Moreover, when two or more kinds of dispersing aids are mixed and used, the mixing ratio may be appropriately adjusted depending on the purpose.

The amount of the dispersion aid used is not particularly limited, but is preferably 0.001 to 0.500 parts by weight, more preferably 0.010 to 0.200 parts by weight, relative to 100 parts by weight of the resin particles. . In order to further improve the effect of suppressing coalescence between resin particles, it is preferable to use the dispersant and the dispersing aid together.

A plasticizer may be used in this production method. The use of a plasticizer has the advantage that the density of the expanded beads can be easily reduced, that is, the expansion ratio of the expanded beads can be easily improved.

Plasticizers used in this production method, or plasticizers preferably used, include the plasticizers described in the section (Additives) of <Poly(3-hydroxyalkanoate)-based resin particles>.

The amount of the plasticizer to be used is not particularly limited, but it is more than 0 parts by weight, preferably 20 parts by weight or less, preferably 1 part by weight to 20 parts by weight, and 2 parts by weight to 15 parts by weight with respect to 100 parts by weight of the resin particles. is more preferred, and 3 to 10 parts by weight is even more preferred. The resin particles used in the dispersing step may already contain a plasticizer before the dispersing step. When the resin particles to be used already contain a plasticizer before the dispersing step, the total amount of the plasticizer already contained in the resin particles before the dispersing step and the plasticizer used in the dispersing step is , preferably satisfies the above range.

(Temperature rising-pressurizing step and holding step)
It is preferable that the present production method further includes a temperature raising/pressurizing step of raising the temperature inside the container to a constant temperature and increasing the pressure inside the container to a constant pressure. It is more preferable that the production method further includes a holding step of holding the temperature and pressure in the container at a constant temperature and a constant pressure, in addition to the temperature rising-pressurizing step. The temperature raising-pressurization step is preferably performed after the dispersing step, and the holding step is preferably performed after the temperature raising-pressurization step. In this specification, the (a) constant temperature in the heating-pressurizing step and the holding step may be referred to as the foaming temperature, and the (b) constant pressure may be referred to as the foaming pressure.

The foaming temperature cannot be defined unconditionally because it varies depending on the type of P3HA, the type of foaming agent, the desired apparent density of the foamed particles, and the like. The expansion temperature is preferably lower than the temperature (Tmh) of the high-temperature side melting peak or the highest melting peak in the DSC measurement described later of the expanded beads, and is the melting point (Tmp) of the resin beads before foaming. It is preferable that the temperature is lower than The foaming temperature is, for example, preferably (Tmp-40.0)°C to Tmp°C, more preferably (Tmp-30.0)°C to (Tmp-10.0)°C, and (Tmp-20.0)°C to (Tmp-15.0)°C is more preferred, and (Tmp-19.0)°C to (Tmp-16.0)°C is most preferred. When the expansion temperature is (Tmp-40.0)° C. or higher, there is a tendency to obtain expanded particles having a suitable density. On the other hand, when the foaming temperature is Tmp° C. or lower, there is no risk of hydrolysis of the resin particles in the container. The expansion temperature has a correlation with the DSC ratio of the obtained expanded beads, and greatly affects the value of the DSC ratio. Therefore, it is desirable to strictly set the expansion temperature in consideration of the DSC ratio of the obtained expanded beads.

In the temperature raising-pressurizing step, the rate at which the temperature is raised to the desired foaming temperature (hereinafter sometimes referred to as temperature raising rate) is preferably 1.0° C./min to 3.0° C./min. 5° C./min to 3.0° C./min is more preferable. If the heating rate is 1.0° C./min or more, the productivity is excellent. On the other hand, if the heating rate is 3.0° C./min or less, impregnation of the foaming agent into the resin particles and reaction between the organic peroxide and P3HA will not be insufficient during the heating.

The foaming 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), and 2.5 MPa (gauge pressure). ~ 4.5 MPa (gauge pressure) is more preferable, 3.0 MPa (gauge pressure) ~ 4.0 MPa (gauge pressure) is more preferable, and 3.2 MPa (gauge pressure) ~ 3.5 MPa (gauge pressure) is even more preferable. , 3.2 MPa (gauge pressure) to 3.4 MPa (gauge pressure) are particularly preferred. If the foaming pressure is 1.0 MPa (gauge pressure) or more, expanded beads having a suitable density can be obtained.

In the holding step, the time (holding time) for holding the dispersion in the container near the foaming temperature and foaming pressure is not particularly limited. The retention time can also be said to be the "retention time" in the term (DSC ratio) described later. The retention time is preferably 1 minute to 120 minutes, more preferably 30 minutes to 120 minutes, even more preferably 45 minutes to 90 minutes. If the holding time is 1 minute or longer, there is no possibility that unreacted organic peroxide will remain. On the other hand, if the time is 120 minutes or less, there is no risk of excessive hydrolysis of P3HA contained in the resin particles.

(Release process)
Preferably, the manufacturing method further comprises a releasing step of releasing one end of the container to release the dispersion in the container to a region of pressure lower than the foaming pressure (ie, the internal pressure of the container). The releasing step is preferably carried out after the heating-pressurizing step or after the holding step. The expulsion step can cause the resin particles to expand, resulting in expanded particles.

In the ejection process, "area under pressure lower than the foaming pressure" intends "area under pressure lower than the foaming pressure" or "space under pressure lower than the foaming pressure", and "atmosphere at pressure lower than the foaming pressure". It can also be called "lower". The region of pressure lower than the foaming pressure is not particularly limited as long as the pressure is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure.

In the ejection process, when the dispersion is ejected to a region with a pressure lower than the foaming pressure, the dispersion is passed through an 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 expansion ratio of the resulting expanded beads. can also be emitted. When resin particles having a relatively high melting point are used, the low-pressure region (space) may be filled with saturated steam for the purpose of improving foamability.

In this manufacturing method, the steps from the above-described dispersing step to the releasing step may be collectively referred to as a "foaming step". The foaming step can also be said to be a step of foaming resin particles using a cross-linking agent.

(Two-step foaming process)
In this manufacturing method, expanded particles having a desired apparent density may not be obtained by the expansion step alone. In that case, the production method may further include a two-step expansion step of further expanding the expanded beads obtained in the expansion step. The two-stage expansion step is not particularly limited as long as the expanded beads obtained in the expansion step are further expanded to obtain expanded beads having an apparent density even smaller than that of the expanded beads obtained in the expansion step. Examples of the two-stage expansion process include the following aspects: (s1) supplying expanded particles obtained in the expansion process into a container; (s2) introducing air or an inorganic gas such as carbon dioxide into the container; (s3) In step (s2), the expanded beads are impregnated with the inorganic gas, and the pressure inside the expanded beads (hereinafter sometimes referred to as "internal pressure of expanded beads"). (s4) After that, the expanded beads are heated with steam or the like to be further expanded to obtain expanded beads having a desired apparent density. The expanded beads obtained in the two-step expansion process are sometimes called two-step expanded beads. Further, when the two-step expansion process is performed, the expansion process may be referred to as a one-step expansion process, and the expanded beads obtained in the one-step expansion process may be referred to as one-step expanded beads.

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

In the two-step foaming step (in s2 and s3 above), the temperature in 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 40°C. ~90°C is more preferred.

In the two-step expansion step (in s4), the pressure of steam or the like for heating the expanded beads (hereinafter sometimes referred to as "two-step expansion pressure") varies depending on the properties of the expanded beads used and the desired apparent density. , cannot be defined unconditionally. The two-stage foaming pressure is preferably 0.01 MPa (gauge pressure) to 0.17 MPa (gauge pressure), more preferably 0.03 MPa (gauge pressure) to 0.11 MPa (gauge pressure).

The DSC ratio, gel fraction and apparent density of the two-step expanded beads are preferably the same as the DSC ratio, gel fraction and apparent density of the expanded beads, respectively. That is, as the DSC ratio, gel fraction and apparent density of the two-stage expanded beads, the descriptions in the terms of (DSC ratio), (gel fraction) and (density) can be used as appropriate.

[3. Poly(3-hydroxyalkanoate)-based expanded particles]
<Physical properties>
The physical properties of the expanded beads are described below.

(Gel fraction)
The present expanded beads are preferably manufactured using a cross-linking agent as described above. When producing expanded beads using a cross-linking agent, the resulting expanded beads may have a cross-linked structure. That is, the expanded beads preferably have a crosslinked structure. In this specification, the crosslinked structure of the expanded beads is evaluated by the gel fraction of the expanded beads. That the expanded beads have a crosslinked structure means that the gel fraction of the expanded beads is 1% by weight or more with respect 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 60% to 75% by weight with respect to 100% by weight of the expanded beads. % by weight is more preferred. When the gel fraction of the expanded beads is (a) 30% by weight or more with respect to 100% by weight of the expanded beads, the molding temperature range of the expanded beads that can provide a good-quality expanded molded article when molding the expanded molded article. (b) When the content is 80% by weight or less, there is an advantage that a foam molded article having excellent internal fusion bondability can be obtained with a low molding pressure.

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

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

(density)
The density (apparent density) of the 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 . is more preferably 0.050 g/cm ³ to 0.100 g/cm ³ . When the density of the expanded particles is (a) 0.030 g/cm ³ or more, there is an advantage that a foam molded article having excellent cushioning properties and/or mechanical strength tends to be obtained; When it is 600 g/cm ³ or less, there is an advantage that a foamed molded article having excellent lightness tends to be obtained. If foamed beads with a desired density cannot be obtained by one-time foaming, the foamed beads that have been foamed once may be subjected to the second and subsequent two-step foaming processes.

In this specification, the method for measuring the density of expanded particles is as follows (1) to (3): (1) Prepare a graduated cylinder filled with ethanol, and add weight W ( g) Submerging the expanded beads; (2) Vd (cm ³ ) is the volume of the expanded beads read from the ethanol water level rise (submersion method); (3) The density of the expanded beads is calculated by the following formula: calculate;
Density (g/cm ³ )=Wd/Vd.

The shape of the expanded beads is not particularly limited, but the ratio of length to diameter (length/diameter) is preferably 1.0 to 2.0, more preferably 1.0 to 1.5. When the length/diameter of the expanded beads is 1.0 to 2.0, there is an advantage that the filling of the molding space of the mold of the molding machine is good, and a foam molded product with good surface beauty can be obtained. . Furthermore, as the length/diameter of the expanded beads approaches 1.0 to 1.2, particularly closer to 1.0, the voids between the expanded beads tend to become smaller in the foamed article obtained from the expanded beads. As a result, it has the advantage of excellent cushioning properties and/or mechanical strength. Here, the length of the foamed bead is intended to be the length of the linear distance between two points when arbitrary two points are selected so that the linear distance between the two points is the longest in the expanded bead. Next, assuming that the length direction of the expanded beads is the x direction, draw an arbitrary straight line y and a straight line z perpendicular to the straight line y on a cross section (cross section x) perpendicular to the x direction. A line segment obtained by cutting the straight line y at the cross section x is called a line segment y, and a line segment obtained by cutting the straight line z at the cross section x is called a line segment z. The diameter of the foamed beads means the average value of the length of the line segment y and the length of the line segment z.

(DSC ratio)
The 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 high temperature side is referred to as the "heat of fusion on the high temperature side", and the heat of fusion obtained from the melting peak on the low temperature side is referred to as the "heat of fusion on the low temperature side". When there are three or more melting peaks, the heat of fusion obtained from the highest melting peak is defined as the "heat of fusion on the high temperature side", and the heat of fusion obtained from the other melting peaks is defined as the heat of fusion on the low temperature side. and

Although the DSC ratio of the present expanded beads is not particularly limited, it is preferably 0.5% to 40.0%, more preferably 0.7% to 30.0%, and 1.0% to 25%. 0% is more preferred, and 1.0% to 23.0% is particularly preferred. When the DSC ratio of the expanded beads is 0.5% or more, there is an advantage that the expanded expanded beads do not coalesce in the expansion step. On the other hand, when the DSC ratio of the expanded beads is 40% or less, there is an advantage that there is a tendency to obtain a foamed molded article having excellent internal fusion bondability at a low molding pressure.

As used herein, the DSC ratio means the ratio of the heat of fusion on the high temperature side to the total heat of fusion calculated from the DSC curve of the expanded beads. In this specification, the DSC ratio is calculated by the following formula (1),
DSC ratio (%) = (heat of fusion on high temperature side/total heat of fusion) x 100 (1),
In the above formula (1), the heat of fusion on the high temperature side and the total heat of fusion are heat amounts obtained from the DSC curve of the poly(3-hydroxyalkanoate)-based foamed particles.

As used herein, the DSC curve is obtained using a differential scanning calorimeter (eg DSC6200 manufactured by Seiko Instruments Inc.). More specifically, in the present specification, the method of measuring (calculating) the DSC ratio of expanded beads using a differential scanning calorimeter (eg DSC6200 manufactured by Seiko Instruments Inc.) is as follows (1) to (6). (1) Weigh 5 mg to 6 mg of expanded beads; (2) Raise the temperature of expanded beads from 10.0° C. to 190.0° C. (3) As shown in FIG. 2, in the DSC curve of the expanded beads obtained in the process of (2), the point representing the temperature before the start of melting and the point representing the temperature after the end of melting are drawn into a straight line. (4) Draw a straight line perpendicular to the X axis that passes through the maximum point between the melting peak on the high temperature side or the highest temperature melting peak and the adjacent melting peak; (5 ) The amount of heat calculated from the area on the high temperature side surrounded by the straight line passing through the baseline and the maximum point and the DSC curve is defined as the heat of fusion on the high temperature side (J / g), and the straight line passing through the baseline and the maximum point and the DSC curve The amount of heat calculated from the enclosed low temperature side area is the low temperature side heat of fusion (J / g), and the heat amount calculated from the area surrounded by the baseline and the DSC curve is the total heat of fusion (J / g) (= high temperature (6) Calculate the DSC ratio from the following formula (1):
DSC ratio (%)=(heat of fusion on high temperature side/total heat of fusion)×100 (1).

FIG. 2 is a diagram showing the DSC curve of P3HA-based expanded beads and the heat of fusion on the high temperature side measured therefrom. The DSC curve shown in Figure 2 has two melting peaks.

The temperature (melting point) of the high temperature side melting peak or the highest melting peak (hereinafter sometimes referred to as "Tmh") in the above-described DSC measurement of the expanded beads is higher than the melting point (Tmp) of the resin particles before foaming. is preferably high. 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 less, more preferably (Tmp+13.0)° C. or less.

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

The method for controlling Tmh within the above-described range is not particularly limited, but is mainly by adjusting the foaming temperature, the foaming pressure, or the time (retention time) during which the dispersion in the container is held near the foaming temperature and the foaming pressure. method.

The DSC ratio of the present expanded beads is also a value that serves as a measure of the amount of crystals having a high melting point contained in the expanded beads. That is, the fact that the DSC ratio is 0.5% to 40.0% indicates that the expanded beads contain a relatively large amount of crystals with a high melting point. Further, the DSC ratio of the expanded beads is greatly related to the viscoelasticity of the resin beads and the expanded beads when the resin beads are expanded and when the expanded beads are expanded. That is, when the DSC ratio of the expanded beads is 0.5% to 40.0%, the resin beads and the expanded beads have excellent expandability when the resin beads are expanded and when the expanded beads are molded. and expandable. As a result, the expanded beads have the advantage that it is possible to obtain a foam molded article having excellent internal fusion bondability and excellent mechanical strength such as compressive strength at a low molding pressure.

In the present expanded beads, methods for controlling the DSC ratio within a predetermined range include a method of adjusting conditions during expansion (particularly expansion temperature and expansion pressure) and/or a holding time described later, and a release step described later. A method of adjusting the temperature of the area (space) where the foamed particles are released in is mentioned. From the viewpoint of ease of adjustment, the preferred method for controlling the DSC ratio within a predetermined range is to adjust the foaming conditions and/or the holding time.

For example, if the foaming temperature is increased, the DSC ratio tends to decrease, and conversely, if the foaming temperature is decreased, the DSC ratio tends to increase. This is because the amount of unmelted crystals varies with the foaming temperature. Also, when the foaming pressure is increased, the DSC ratio tends to decrease, and conversely, when the foaming pressure is decreased, the DSC ratio tends to increase. This is because the foaming pressure changes the degree of plasticization, which in turn changes the amount of unmelted crystals.

Also, the DSC ratio tends to increase as the retention time increases. This is because the growth amount of unmelted crystals changes depending on the holding time.

[4. Method for producing poly(3-hydroxyalkanoate) foam molded product]
The method for producing a poly(3-hydroxyalkanoate)-based foamed molded product of the present invention comprises [2. Method for producing expanded poly(3-hydroxyalkanoate)-based beads] and the poly(3-hydroxyalkanoate)-based expanded beads obtained by )-based foamed particles are heated in a mold and molded.

The step of heating and molding the P3HA-based expanded particles in a mold is not particularly limited, and known methods can be applied. For example, there is a production method (in-mold foam molding method) including the following (b1) to (b6) in order, but the production method is not limited to this:
(a1) A mold composed 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. Here, the fixed mold and the movable mold form portions with different lengths in the driving direction of the movable mold when the movable mold is driven toward the fixed mold (this operation is sometimes referred to as "mold closing"). a fixed closed space can be formed inside the fixed mold and the mobile mold;
(a2) A slight gap (for example, a gap of 10 mm in the thickness direction of the bottom of the foam molded product or in the height direction of the vertical wall portion (also referred to as cracking) so that the fixed mold and the moving mold are not completely closed. ) is formed, driving the moving mold towards the fixed mold;
(a3) filling foamed particles that have not been pressurized with air into the molding space formed inside the stationary mold and the moving mold, for example through a filling machine;
(a4) drive the movable mold so that the fixed mold and the movable mold are completely closed (that is, the mold is completely closed);
(a5) After preheating the mold with steam, the mold is subjected to one-way heating and reverse one-way heating with steam, and then double-sided heating of the mold with steam to perform in-mold foam molding;
(a6) The in-mold foam-molded product is removed from the mold and dried (for example, dried at 75° C.) to obtain a foam-molded product.

In the above (a5), "water vapor pressure during one-way heating and reverse one-way heating" is defined as "water vapor pressure A", and "water vapor pressure during double-sided heating" is designated as "water vapor pressure B".

Although the pressure of the water vapor pressure A is not particularly limited, it is preferably 0.01 MPa (gauge pressure) to 0.15 MPa (gauge pressure), and 0.02 MPa (gauge pressure) to 0.13 MPa (gauge pressure). more preferably 0.04 MPa (gauge pressure) to 0.13 MPa (gauge pressure). This configuration has the advantage of tending to yield a foam molded article with a high internal fusion rate. In particular, by setting the steam pressure A to about 1/2 of the steam pressure B at the time of in-mold foam molding, excessive pressurization is not required, which is economically advantageous, and the internal fusion rate is improved. It is preferable because it can provide a high foaming molded product.

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. Although the lower limit of the water vapor pressure B is not particularly limited, it is preferably 0.08 MPa (gauge pressure) or more, more preferably 0.10 MPa (gauge pressure) or more. When the lower limit value of the water vapor pressure B is within the above-described range, there is an advantage that a foamed molded article having a high internal fusion rate and excellent impact resistance tends to be obtained.

As the manufacturing method including the above (a1) to (a6), the method of filling the molding space of the mold with foamed particles that have not been pressurized with air has been described. , the expanded particles may be subjected to pressure treatment. The method for producing a P3HA-based foam molded product according to an embodiment of the present invention may be, for example, the following production methods (b1) to (b3).
(b1) The expanded beads (including the two-step expanded beads described above; the same shall apply hereinafter) are pressurized with an inorganic gas to impregnate the expanded beads with the inorganic gas, and after applying a predetermined internal pressure to the expanded beads, the A method of filling a mold with foamed particles and heating the mold with steam;
(b2) A method of filling foamed particles into a mold, compressing the mold so as to reduce the volume in the mold by 10% to 75%, and then heating the mold with steam;
(b3) A method in which foamed particles are compressed under gas pressure and filled in a mold, and the mold is heated with steam using the resilience of the expanded particles.

As the inorganic gas in (b1), at least one selected from the group consisting of air, nitrogen, oxygen, carbon dioxide, helium, neon, argon and the like can be used. Among these, air or carbon dioxide is preferred.

The internal pressure of the expanded beads in (b1) is preferably 0.10 MPa (absolute pressure) to 0.30 MPa (absolute pressure), more preferably 0.11 MPa (absolute pressure) to 0.25 MPa (absolute pressure).

In the above (b1), the temperature in the container when impregnating the foamed particles with the inorganic gas is preferably 10°C to 90°C, more preferably 40°C to 80°C.

[5. Poly(3-hydroxyalkanoate) foam molded product]
The poly(3-hydroxyalkanoate)-based foamed molded article of the present invention can be prepared according to [4. Production method of poly(3-hydroxyalkanoate)-based foam molded article]. The P3HA-based foamed molded article obtained in this manner has an excellent fusion rate and excellent mechanical properties such as impact resistance and compressive strength.

EXAMPLES The present invention will be specifically described below with reference to examples, but the technical scope of the present invention is not limited by these examples.

〔material〕
Substances used in Examples and Comparative Examples are shown below.

(Poly(3-hydroxyalkanoate))
P3HA: P3HB3HH (produced by the inventor, monomer ratio 3HB/3HH = 95/5 (mol%/mol%), melting point 145.0°C)
P3HA was produced according to the method described in paragraphs [0064] to [0125] of International Publication WO2009/145164.

(Additive)
Pentaerythritol (Neurizer P: Mitsubishi Chemical Corporation)
Behenamide (manufactured by Tokyo Chemical Industry Co., Ltd.)
Erucamide (manufactured by Tokyo Chemical Industry Co., Ltd.)

(Air bubble control agent)
Talc (Talcan powder PKS manufactured by Hayashi Kasei Co., Ltd.)

(Crosslinking agent (organic peroxide))
t-butyl peroxy-2-ethylhexyl carbonate (TBEC: manufactured by Arkema Yoshitomi Co., Ltd., Luperox TBEC)

(foaming agent)
Carbon dioxide (manufactured by Air Water Inc.)

(Inorganic dispersant)
Aluminum oxide-1 (manufactured by Evonik, AEROXIDE AluC: specific gravity 3.9 / pH 5)
Aluminum oxide-2 (manufactured by Sumitomo Chemical Co., Ltd., AKP-20: specific gravity 3.9 / pH 6)
Aluminum oxide-3 (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., specific gravity 3.9 / pH 10)
Titanium oxide (produced by Tayka, JR: specific gravity 4.2/pH 8.5)
Barium sulfate (manufactured by Takehara Chemical Industry Co., Ltd., W-1: specific gravity 4.5 / pH 8)
Tertiary calcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd., specific gravity 3.1/pH 6)
Kaolin (manufactured by BASF, ASP-170: specific gravity 2.6/pH 7.5)

(dispersion aid)
Sodium alkanesulfonate (Latemul PS manufactured by Kao Corporation)

〔Measuring method〕
Evaluation methods performed in Examples and Comparative Examples are described below.

(Measurement of hydrogen ion concentration of inorganic dispersant)
The hydrogen ion concentration of the inorganic dispersant was measured by mixing the inorganic dispersant with pure water to form a 4% by weight dispersion, and using a pH meter (KS723 manufactured by Shindengen Electric Manufacturing Co., Ltd.).

(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 mg to 6 mg of resin particles were weighed; (2) the temperature of the resin particles was increased by 10.0° C./min. (3) In the DSC curve obtained in the process of (2) above, the temperature of the highest melting peak of the resin particles was melting point.

(Amount of resin remaining in pressure-resistant container (percentage))
The method for measuring the residual resin amount (percentage) in the pressure vessel was as follows (1) to (3): Measure the weight Y (g); (2) Recover the entire amount of P3HA resin particles remaining in the pressure container after the foaming step (release step), and dry the weight y in a dryer at 75° C. for 24 hours. (g) was measured; (3) the amount (percentage) of resin remaining in the pressure vessel was calculated and evaluated by the following formula;
Residual resin amount (percentage) in the pressure container = 100 x y/Y.
◎: Residual resin amount (percentage) in the pressure vessel is less than 0.2% ○: Residual resin amount (percentage) in the pressure vessel is 0.2% or more and less than 0.8% △: Pressure vessel Residual resin amount (percentage) in the pressure vessel is 0.8% or more and less than 1.5% × ... Residual resin amount (percentage) in the pressure vessel is 1.5% or more

(Measurement of DSC ratio of expanded beads)
A differential scanning calorimeter (DSC6200 manufactured by Seiko Instruments Inc.) was used to measure (calculate) the DSC ratio of the expanded beads. The measurement (calculation) method of 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; (2) Foaming The temperature of the particles was increased from 10.0° C. to 190.0° C. at a heating rate of 10.0° C./min to melt the expanded particles; In the DSC curve, a baseline was created by connecting the point representing the temperature before the start of melting and the point representing the temperature after the end of melting with a straight line; (4) the melting peak on the high temperature side or the highest melting peak and the adjacent melting A straight line passing through the maximum point between the peaks was drawn in the direction perpendicular to the X-axis; is the heat of fusion on the high temperature side (J / g), and the heat quantity calculated from the area surrounded by the baseline and the DSC curve is the total heat of fusion (J / g); (6) Calculate the DSC ratio from the following equation bottom:
DSC ratio (%)=(heat of fusion on high temperature side/total heat of fusion)×100.

(Measurement of gel fraction of expanded particles)
The method for measuring the gel fraction of the expanded beads was as follows (c1) to (c5): (c1) 1 g of expanded beads and 100 ml of chloroform were placed in a 150 ml flask; (c2). The mixture in the flask was heated under reflux at 62° C. under atmospheric pressure for 8 hours; (c3) the resulting heat-treated product was filtered using a suction filtration device equipped with a 100-mesh wire mesh; (c4) on a wire mesh The filtered product 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; (c5) The gel fraction was calculated by the following formula:
Gel fraction (% by weight)=100×Wg/1.

(Measurement of density of expanded particles)
The method for measuring the density of the expanded beads was as follows (1) to (3): (1) Prepare a graduated cylinder filled with ethanol, and add Wd (g) of expanded beads to the ethanol. (2) Vd (cm ³ ) was the volume of the expanded beads read from the amount of water level rise in ethanol (submersion method); (3) The density of the expanded beads was calculated by the following formula;
Density (g/cm ³ )=Wd/Vd.

(Fusion rate of foam molding)
The fusion rate of the foam molded body was measured as follows (1) to (4): (1) The foam molded body (approximately 370 mm long x 320 mm wide x 60 mm thick) was cut with a cutter in the thickness direction. (2) Then, the foam molded article was broken by hand along the cut; The total number of expanded beads present in the observation plane and the number of expanded beads broken outside the particle interface (that is, expanded beads themselves broken) were counted in the observation plane; (4) below. Calculate the internal fusion rate based on the formula;
Fusion rate (%)=(the number of expanded particles broken outside the particle interface in the observation plane/the total number of expanded particles present in the observation plane)×100.

[Example 1]
(Resin particle preparation step)
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, 1.0 parts by weight of pentaerythritol, 0.50 parts by weight of behenamide, 0.50 parts by weight of erucamide, and 0.10 parts by weight of talc were weighed and dry blended. Thus, a P3HA-based composition was prepared. The prepared P3HA-based composition was supplied to a twin-screw extruder, and the P3HA-based composition was melt-kneaded at a cylinder setting temperature of 130° C. to 160° C. (melt-kneading step). A melt-kneaded P3HA-based composition at 179° C. was extruded from a die nozzle attached to the tip of the extruder. The ejected P3HA-based composition was cooled with water at 50° C. and then cut into cylindrical P3HA-based resin particles each weighing 3.5 mg and having a length/diameter of 2.0. obtained (particle forming step). Also, the melting point of the P3HA resin particles was 145.0°C.

(foaming process)
100 parts by weight (2.5 kg) of the P3HA resin particles obtained in the above (resin particle preparation step), 200 parts by weight of pure water as an aqueous dispersion medium, and 2.0 parts by weight of TBEC as a cross-linking agent (organic peroxide) Then, 1.0 parts by weight of aluminum oxide-1 as an inorganic dispersant and 0.05 parts by weight of sodium alkanesulfonate as a dispersing agent are fed into a pressure vessel with an internal volume of 10 L and equipped with a stirring blade, and the stirring blade is added. was rotated at 200 rpm to stir the raw materials in the pressure vessel. Thereafter, the contents (dispersion liquid) in the pressure vessel were continuously stirred until the discharge of the dispersion liquid was completed.

After introducing nitrogen into the pressure vessel, the pressure vessel was evacuated to remove oxygen in the pressure vessel. Further, carbon dioxide was supplied as a foaming agent into the pressure vessel to prepare a dispersion (dispersion step). After that, the temperature inside the pressure vessel was raised to the foaming temperature of 129.0°C. Further, 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 increase-increase process). Then, the temperature and pressure inside the pressure vessel were held at around the foaming temperature and foaming pressure, respectively, for 30 minutes (holding step). After the holding step, the valve at the bottom of the pressure vessel was opened, and the dispersion liquid in the pressure vessel was released under atmospheric pressure through an open orifice with a diameter of 3.6 mm to obtain expanded P3HA particles (release step).

After the discharge step was completed, the total amount of resin particles remaining in the pressure vessel was recovered, and the residual resin amount (ratio) in the pressure vessel was calculated.

On the other hand, the obtained expanded beads were dried at 75° C. after washing the inorganic dispersant and the like adhering to the surfaces of the expanded beads with an aqueous solution of sodium hexametaphosphate and water. The resulting expanded beads had a length/diameter of 1.0 and a spherical or nearly spherical shape. The heat of fusion on the high temperature side, the DSC ratio, the gel fraction, and the density of the obtained expanded beads were measured. Table 1 shows the results.

(Production of P3HA-based foamed molded product)
370mm long x 320mm wide x
A mold having a molding space with a thickness of 60 mm was filled with the expanded particles obtained in the above (expansion step) without pressure treatment. The filled foamed particles were heated with steam of 0.15 MPa (gauge pressure) to obtain a foamed molding. After drying the obtained foam molded article at 75° C. for 24 hours, it was cured at 23° C. and the fusion rate was evaluated.

[Example 2]
Expanded beads and an expanded molded product were produced in the same manner as in Example 1, except that the number of revolutions of the stirring blade was changed to 260 rpm, and their physical properties were measured. Table 1 shows the results.

[Example 3]
An expanded bead and an expanded molded product were produced in the same manner as in Example 2 except that the expansion temperature was 130.0° C. and the expansion pressure was 3.5 MPa (gauge pressure), and their physical properties were measured. Table 1 shows the results.

[Example 4]
Expanded beads and expanded molded articles were produced in the same manner as in Example 2 except that 170 parts by weight of pure water was used as the aqueous dispersion medium, and their physical properties were measured. Table 1 shows the results.

[Example 5]
Expanded beads and an expanded molded product were produced in the same manner as in Example 2, except that 150 parts by weight of pure water was used as the aqueous dispersion medium, and each physical property was measured. Table 1 shows the results.

[Example 6]
Expanded beads and expanded molded articles were produced in the same manner as in Example 2, except that 0.7 parts by weight of aluminum oxide-1 was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Example 7]
Expanded beads and expanded molded articles were produced in the same manner as in Example 4, except that 1.0 part by weight of aluminum oxide-2 was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Example 8]
Expanded beads and expanded molded articles were produced in the same manner as in Example 4, except that 1.0 part by weight of aluminum oxide-3 was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Example 9]
Expanded beads and an expanded molded product were produced in the same manner as in Example 4, except that 1.0 part by weight of titanium oxide was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Example 10]
Expanded beads and expanded molded articles were produced in the same manner as in Example 4, except that 1.0 part by weight of barium sulfate was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Comparative Example 1]
Expanded beads and expanded molded articles were produced in the same manner as in Example 1, except that 1.0 part by weight of tribasic calcium phosphate was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Comparative Example 2]
Expanded beads and expanded molded articles were produced in the same manner as in Example 4, except that 1.0 part by weight of tribasic calcium phosphate was used as the inorganic dispersant, and their physical properties were measured. Table 1 shows the results.

[Comparative Example 3]
Expanded beads and an expanded molded article were produced in the same manner as in Example 4, except that kaolin was used as an inorganic dispersant at 1.0 part by weight, and each physical property was measured. Table 1 shows the results.

According to the present invention, P3HA-based expanded beads can be provided with good production efficiency. Foamed articles obtained by in-mold foam molding of the foamed particles are suitable for food containers, packaging materials, sanitary goods, garbage bags, cushioning materials for packaging, agricultural product boxes, fish boxes, automobile members, construction materials, civil engineering materials, and the like. can be used for

Claims (6)

A method for producing poly(3-hydroxyalkanoate)-based expanded beads, comprising:
A dispersing step of dispersing poly(3-hydroxyalkanoate) resin particles, an aqueous dispersion medium, an inorganic dispersant, and a foaming agent in a pressure vessel,
A method for producing poly(3-hydroxyalkanoate) expanded particles, wherein the inorganic dispersant has a specific gravity of 3.5 or more and 5.0 or less. 2. The method for producing poly(3-hydroxyalkanoate) expanded particles according to claim 1, wherein the inorganic dispersant is at least one selected from the group consisting of aluminum oxide, titanium oxide and barium sulfate. 2. The method for producing poly(3-hydroxyalkanoate) expanded particles according to claim 1, wherein the inorganic dispersant is aluminum oxide. Production of poly(3-hydroxyalkanoate)-based expanded particles according to any one of claims 1 to 3, wherein the inorganic dispersant has a hydrogen ion concentration (pH) of less than 7.5. Method. Claims 1 to 4, wherein in the dispersing step, the amount of the aqueous dispersion medium used is 130 parts by weight or more and less than 200 parts by weight with respect to 100 parts by weight of the poly(3-hydroxyalkanoate) resin particles. A method for producing poly(3-hydroxyalkanoate)-based expanded beads according to any one of the above items. a step of producing poly(3-hydroxyalkanoate)-based expanded particles by the production method according to any one of claims 1 to 5;
A method for producing a poly(3-hydroxyalkanoate)-based expanded molded article, comprising a step of heating and molding the expanded particles in a mold.

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