Method for producing poly(3-hydroxyalkanoate)-based expanded particles or poly(3-hydroxyalkanoate)-based expanded molded articles

Abstract

Poly(3-hydroxyalkanoate)-based expanded particles are produced by charging a foaming agent to an aqueous dispersion that comprises resin particles each comprising a poly(3-hydroxyalkanoate) and a crosslinking agent in a pressure-tight container, heating the content in the pressure-tight container to a predetermined temperature ranging from 130 to 150℃, retaining the heated content for 5 to 55 minutes at the predetermined temperature, and release one end of the pressure-tight container to discharge the content in the pressure-tight container to an atmosphere having a low pressure, thereby expanding the resin particles. The poly(3-hydroxyalkanoate) is a mixture which contains a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer at a weight ratio of 99:1 to 80:20, and the crosslinking agent is an organic peroxide such as a percarbonate.

Description

Technical Field

[0001] The present invention relates to a method for producing poly(3-hydroxyalkanoate)-based foamed particles by foaming resin particles composed of a poly(3-hydroxyalkanoate)-based composition, and a method for producing a poly(3-hydroxyalkanoate)-based foamed molded article by molding the foamed particles.

Background Art

[0002] Petroleum-derived plastics are discarded in large quantities every year, and the shortage of landfill sites and environmental pollution caused by these large amounts of waste have been taken up as serious problems. In recent years, microplastics have become a major problem in the marine environment. For this reason, biodegradable plastics that are decomposed by the action of microorganisms in the environment such as the sea and soil, landfill sites, and compost are attracting attention. Biodegradable plastics are being developed with the aim of wide application to materials for agriculture, forestry, and fisheries used in the environment, food containers, packaging materials, sanitary products, garbage bags, etc. that are difficult to recycle after use. Furthermore, foams composed of biodegradable plastics are expected to be used in packaging cushioning materials, agricultural boxes, fish boxes, automotive parts, building materials, civil engineering materials, etc.

[0003] Among the above-mentioned biodegradable plastics, poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as P3HA), which is a plant-derived plastic, has attracted attention from the viewpoints of excellent biodegradability and carbon neutrality. Among them, poly(3-hydroxybutyrate) (hereinafter sometimes referred to as P3HB), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (hereinafter sometimes referred to as P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as P3HB3HH), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter sometimes referred to as P3HB4HB), etc. have attracted attention.

[0004] It has been considered to apply the above biodegradable plastics to foamed product applications. For example, Patent Document 1 discloses poly(3-hydroxyalkanoate) - based foamed particles and poly(3-hydroxyalkanoate) - based foamed molded articles having a gel fraction and a heat of fusion within specific ranges.

[0005] Further, Patent Document 2 discloses poly(3-hydroxyalkanoate) resin foamed particles comprising a resin composition containing poly(3-hydroxyalkanoate) and an isocyanate compound and having a melt viscosity of a specific value or more.

Prior Art Documents

Patent Documents

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] In Patent Document 1, it has been reported that by setting the gel fraction and the heat of fusion of poly(3-hydroxyalkanoate) - based foamed particles within specific ranges, a poly(3-hydroxyalkanoate) - based foamed molded article having good surface properties and a small molding shrinkage rate can be obtained. However, the present inventors have confirmed that since the foamed particles described in the document are produced using benzoyl peroxide as a crosslinking agent, odors derived from aromatic compounds such as benzene may remain.

[0008] In Patent Document 2, poly(3-hydroxyalkanoate) and an isocyanate compound are melt-kneaded using an extruder or the like to obtain a resin composition having a melt viscosity of a specific value or more, and then the resin composition is foamed using a foaming agent, whereby poly(3-hydroxyalkanoate) resin foamed particles having a wide processing condition range during molding and no post-shrinkage after molding are obtained. However, the isocyanate compound is toxic, and the obtained foamed particles may turn yellow. Further, in the examples of this document, after introducing the foaming agent, it is held at a high temperature and high pressure for 1 hour, and the productivity of the foamed particles is low.

[0009] In view of the above, an object of the present invention is to provide a production method capable of obtaining poly(3-hydroxyalkanoate)-based foamed particles with high productivity and suppressed odor, and a production method of a poly(3-hydroxyalkanoate)-based foamed molded article using the foamed particles.

Means for Solving the Problems

[0010] As a result of intensive studies to solve the above problems, the present inventor has found that by using a specific mixture as poly(3-hydroxyalkanoate) and a specific compound as a cross-linking agent, and in addition, holding at a specific temperature for a specific time after introducing a foaming agent, poly(3-hydroxyalkanoate)-based foamed particles with high productivity and suppressed odor can be obtained, and the present invention has been completed.

[0011] The first invention is a method for producing poly(3-hydroxyalkanoate) foamed particles, which includes a step of introducing a foaming agent into an aqueous dispersion containing resin particles and a crosslinking agent in a pressure-resistant container, a step of heating the content of the pressure-resistant container to a predetermined temperature within the range of 130 to 150 °C and holding it at the predetermined temperature for 5 to 55 minutes, and a step of foaming the resin particles by opening one end of the pressure-resistant container and discharging the content of the pressure-resistant container into a low-pressure atmosphere. The poly(3-hydroxyalkanoate) is a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer in a weight ratio of 99:1 to 80:20, and the crosslinking agent is an organic peroxide of percarbonates. The invention relates to a production method. Preferably, the foaming agent is carbon dioxide. Preferably, the poly(3-hydroxyalkanoate) copolymer is a copolymer of 3-hydroxybutyrate and a comonomer, and the monomer ratio in the copolymer is 3-hydroxybutyrate / comonomer = 99 / 1 to 89 / 11 (mol% / mol%). Preferably, the organic peroxide of percarbonates has a half-life temperature of 150 to 170 °C in 1 minute and is liquid at room temperature. Preferably, the organic peroxide of percarbonates is a compound having one carbonate group. Preferably, after the step of foaming the resin particles, the production method further includes a step of impregnating the obtained foamed particles with an inorganic gas to increase the pressure inside the foamed particles and then heating and expanding the foamed particles. The present invention also relates to a method for producing a poly(3-hydroxyalkanoate) foamed molded article, which includes a step of producing poly(3-hydroxyalkanoate) foamed particles by the above production method and a step of heating and molding the foamed particles in a mold.

Effects of the Invention

[0012] According to the present invention, it is possible to provide a production method capable of obtaining poly(3-hydroxyalkanoate)-based foamed particles with high productivity and suppressed odor, and a production method of a poly(3-hydroxyalkanoate)-based foamed molded article using the foamed particles.

Brief Description of the Drawings

[0013]

Figure 1

Embodiments for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described, but the present invention is not limited to the following embodiments.

[0015] The P3HA-based foamed particles according to the present embodiment can be obtained by foaming resin particles composed of a P3HA-based composition using a foaming agent. Further, the P3HA-based foamed molded article can be obtained by heating and molding the P3HA-based foamed particles in a mold, specifically, by in-mold foaming molding.

[0016] [P3HA] P3HA is a polymer having a 3-hydroxyalkanoate repeating unit as an essential constituent unit (monomer unit), and specifically, a polymer containing a repeating unit represented by the following general formula (1) is preferable. [-CHR-CH2-CO-O-] (1)

[0017] In general formula (1), R represents an alkyl group represented by C p H 2p+1 and p represents an integer of 1 to 15. Examples of R include linear or branched alkyl groups such as a methyl group, an ethyl group, a propyl group, a methylpropyl group, a butyl group, an isobutyl group, a t-butyl group, a pentyl group, and a hexyl group. As p, 1 to 10 is preferable, and 1 to 8 is more preferable.

[0018] As the P3HA, P3HA produced from microorganisms is particularly preferred. The P3HA produced from microorganisms is poly[(R)-3-hydroxyalkanoate] in which all of the 3-hydroxyalkanoate repeating units are (R)-3-hydroxyalkanoates.

[0019] In the present embodiment, as the P3HA, a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer is used. Hereinafter, P3HA refers to the mixture.

[0020] The poly(3-hydroxyalkanoate) copolymer is a copolymer containing at least two types of 3-hydroxyalkanoate units, or a copolymer containing at least one type of 3-hydroxyalkanoate unit and a comonomer unit other than the 3-hydroxyalkanoate unit. The poly(3-hydroxyalkanoate) copolymer preferably contains at least 3-hydroxybutyrate units.

[0021] Specific examples of the poly(3-hydroxyalkanoate) copolymer include, for example, poly(3-hydroxybutyrate-co-3-hydroxypropionate), poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (abbreviation: P3HB3HV), poly(3-hydroxybutyrate-co-3-hydroxyvalerate-3-hydroxyhexanoate), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (abbreviation: 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) (abbreviation: P3HB4HB), and the like. As the poly(3-hydroxyalkanoate) copolymer, one kind may be used alone, or two or more kinds may be used in combination. In particular, from the viewpoints of processability and physical properties of the foamed molded article, poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) and / or poly(3-hydroxybutyrate-co-4-hydroxybutyrate) are preferred, and poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) is particularly preferred.

[0022] When the poly(3-hydroxyalkanoate) copolymer is a copolymer of 3-hydroxybutyrate and a comonomer, the composition ratio of 3-hydroxybutyrate and the comonomer [for example, 3-hydroxyhexanoate (hereinafter sometimes referred to as 3HH) or 4-hydroxybutyrate (hereinafter sometimes referred to as 4HB)], that is, the monomer ratio in the copolymer, is preferably 3-hydroxybutyrate / comonomer = 99 / 1 to 89 / 11 (mol% / mol%), more preferably 97 / 3 to 91 / 9 (mol% / mol%), and even more preferably 95 / 5 to 93 / 7 (mol% / mol%). When the comonomer ratio in the copolymer is 1 mol% or more, the melting processing temperature range and the thermal decomposition temperature range of P3HA are separated, and the processability tends to be good. On the other hand, when the comonomer ratio in the copolymer is 11 mol% or less, the crystallization during melt processing is fast, and the productivity tends to be better.

[0023] Note that each monomer ratio can be determined by a method known to those skilled in the art, for example, the method described in International Publication No. 2013 / 147139.

[0024] The above-mentioned poly(3-hydroxybutyrate) homopolymer is a homopolymer substantially composed of only 3-hydroxybutyrate units (abbreviation: P3HB). However, a copolymer containing a trace amount of a comonomer (specifically, less than 1 mol% as the monomer ratio) is also included in the above-mentioned homopolymer. For a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer, even if the foaming temperature is high, the components derived from the poly(3-hydroxybutyrate) homopolymer are difficult to completely melt, and crystal growth is easy, so the productivity of the foamed particles can be increased.

[0025] In a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer, the weight ratio of the two polymers (copolymer: homopolymer) is preferably from 99:1 to 80:20, more preferably from 98:2 to 84:16, still more preferably from 97:3 to 88:12, and particularly preferably from 96:4 to 90:10 so that foamed particles can be suitably obtained at the foaming temperature at high temperature and the productivity of the foamed particles can be enhanced.

[0026] The melting point of P3HA is not particularly limited, but is preferably from 110 to 170°C, more preferably from 120 to 165°C. When the melting point is less than 110°C, the heating dimensional change of the obtained P3HA-based foamed molded article tends to increase. On the other hand, when the melting point exceeds 170°C, hydrolysis tends to occur easily during the foaming process. The melting point of P3HA is measured as the temperature of the highest-temperature melting peak in the DSC curve obtained when about 5 mg of P3HA is weighed and the temperature is raised from 10°C to 190°C at a rate of temperature increase of 10°C / min using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Sciences Corporation).

[0027] The weight average molecular weight of P3HA is not particularly limited, but is preferably from 200,000 to 2,000,000, more preferably from 250,000 to 1,500,000, and still more preferably from 300,000 to 1,000,000. When the weight average molecular weight is 200,000 or more, the closed cell ratio of the obtained P3HA-based foamed particles tends to be high. On the other hand, when the weight average molecular weight is 2,000,000 or less, the load on the machine during melt processing such as production of resin particles is low and the productivity tends to be high. The weight average molecular weight of P3HA can be measured from the polystyrene-equivalent molecular weight distribution using gel permeation chromatography (HPLC GPC system manufactured by Shimadzu Corporation) using a chloroform solution. As the column in the gel permeation chromatography, a column suitable for measuring the weight average molecular weight may be used.

[0028] The method for producing P3HA is not particularly limited, and it may be a production method by chemical synthesis or a production method by microorganisms. Among them, the production method by microorganisms is preferable as described above. For the production method by microorganisms, known or commonly used methods can be applied.

[0029] For example, as copolymer-producing bacteria of 3-hydroxybutyrate and other hydroxyalkanoates, Aeromonas caviae, which produces P3HB3HV and P3HB3HH, Alcaligenes eutrophus, which produces P3HB4HB, etc. are known. In particular, regarding P3HB3HH, in order to increase the productivity of P3HB3HH, Alcaligenes eutrophus AC32 strain (Alcaligenes eutrophus AC32, FERM BP-6038) (T. Fukui, Y. Doi, J. Bateriol., 179, p4821-4830 (1997)) into which the genes of the P3HA synthase group have been introduced is more preferable, and microbial cells in which P3HB3HH is accumulated in the cells by culturing these microorganisms under appropriate conditions are used. In addition to the above, depending on the P3HA to be produced, genetically modified microorganisms into which various P3HA synthesis-related genes have been introduced may be used, or the culture conditions including the type of substrate may be optimized.

[0030] The method for obtaining a mixture of a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer is not particularly limited, and it may be a method of directly obtaining the mixture by microbial production or a method of directly obtaining the mixture by chemical synthesis. Also, two or more resins may be melt-kneaded using an extruder, kneader, Banbury mixer, roll, etc. to obtain a mixture, or two or more resins may be dissolved in a solvent, mixed, and dried to obtain a mixture. Among them, the method of directly obtaining the mixture by microorganisms as described above is preferable. For the production method by microorganisms, for example, the method described in International Publication No. 2015 / 146195 can be applied.

[0031] [Resin particles composed of a P3HA-based composition] The resin particles composed of the P3HA-based composition are particles composed of a composition (P3HA-based composition) containing P3HA as an essential component. The composition usually contains P3HA and additives as necessary. In the present disclosure, the resin particles refer to particles that have not yet been foamed before being subjected to the foaming process.

[0032] The content of P3HA in the resin particles composed of the P3HA-based composition is not particularly limited, but from the viewpoint of the biodegradability of the obtained foamed particles and foamed molded article, etc., 70% by weight or more is preferable, and more preferably 80% by weight or more.

[0033] The melting point of the resin particles composed of the P3HA-based composition (hereinafter sometimes referred to as Tmp) is not particularly limited, but 110 to 170°C is preferable, and more preferably 120 to 165°C. If the melting point is less than 110°C, the change in the heated dimension of the obtained P3HA-based foamed molded article tends to be large. On the other hand, if the melting point exceeds 170°C, hydrolysis of P3HA tends to occur easily during the foaming process. The melting point of the resin particles composed of the P3HA-based composition is measured as the temperature of the highest-temperature melting peak in the DSC curve obtained when about 5 mg of the resin particles composed of the P3HA-based composition are weighed using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Tech Science Corporation) and the temperature is raised from 10°C to 190°C at a heating rate of 10°C / min.

[0034] The melt flow rate (hereinafter sometimes referred to as MFR) of the resin particles composed of the P3HA-based composition is not particularly limited, but is preferably 1 to 30 g / 10 min (minutes), more preferably 1 to 25 g / 10 min, and still more preferably 1 to 20 g / 10 min. When the MFR is less than 1 g / 10 min, it tends to be difficult to obtain foamed particles with a low apparent density with only one foaming. On the other hand, when the MFR exceeds 30 g / 10 min, the closed cell ratio of the obtained foamed particles tends to be low. The MFR of the resin particles composed of the P3HA-based composition is measured using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho Co., Ltd.) in accordance with JIS K7210 under the conditions of a load of 5 kg and a measurement temperature of the melting end temperature + 1 to 10 °C read from the DSC curve obtained in "Measurement of the melting point of resin particles composed of the P3HA-based composition".

[0035] The weight per particle of the resin particles composed of the P3HA-based composition is preferably 0.3 to 10 mg, more preferably 0.4 to 7.5 mg, and still more preferably 0.5 to 5 mg. When the weight per particle is 0.3 mg or more, the resin particles composed of the P3HA-based composition can be stably produced with high productivity. On the other hand, when the weight per particle is 10 mg or less, it is possible to easily realize thinning of the P3HA-based foam molded body.

[0036] When the shape of the resin particles composed of the P3HA-based composition is cylindrical, the length / diameter of the resin particles is preferably 0.5 to 3, more preferably 0.7 to 2.7, and still more preferably 1 to 2.5. When the length / diameter is less than 0.5, the shape of the obtained foamed particles tends to be flat. On the other hand, when the length / diameter exceeds 3, the shape of the foamed particles tends to be vertically long.

[0037] The resin particles composed of the P3HA-based composition may contain additives as long as the effects of the invention are not inhibited. Examples of the additives include, for example, a foam regulator, a crystallization nucleating agent, a lubricant, a plasticizer, an antistatic agent, a flame retardant, a conductive agent, a heat insulating agent, a crosslinking agent, an antioxidant, an ultraviolet absorber, a colorant, an inorganic filler, an organic filler, a hydrolysis inhibitor, etc., which can be used according to the purpose. In particular, biodegradable additives are preferred.

[0038] Examples of the foam regulator include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, bentonite, etc. Among them, talc is preferred in that its dispersibility in P3HA is particularly excellent. The amount of the foam regulator used is not particularly limited, but is preferably 0.01 to 1 part by weight, more preferably 0.03 to 0.5 part by weight, and still more preferably 0.05 to 0.3 part by weight with respect to 100 parts by weight of P3HA. Also, the foam regulator may be used alone or in combination of two or more, and the mixing ratio can be appropriately adjusted according to the purpose.

[0039] Examples of the crystallization nucleating agent include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, boron nitride, etc. Among them, pentaerythritol is preferred in that its crystallization promoting effect on P3HA is particularly excellent. The amount of the crystallization nucleating agent used is not particularly limited, but is preferably 0.1 to 5 parts by weight, more preferably 0.5 to 3 parts by weight, and still more preferably 0.7 to 1.5 parts by weight with respect to 100 parts by weight of P3HA. Also, the crystallization nucleating agent may be used alone or in combination of two or more, and the mixing ratio can be appropriately adjusted according to the purpose.

[0040] Examples of the lubricant include behenic acid amide, oleic acid amide, erucic acid amide, stearic acid amide, palmitic acid amide, N-stearyl behenic acid amide, N-stearyl erucic acid amide, ethylene bisstearic acid amide, ethylene bisoleic acid amide, ethylene biserucic acid amide, ethylene bislauric acid amide, ethylene biscapric acid amide, p-phenylene bisstearic acid amide, polycondensate of ethylenediamine, stearic acid and sebacic acid, and the like. Among them, behenic acid amide or erucic acid amide is preferable in that the lubricating effect on P3HA is particularly excellent. The amount of the lubricant used is not particularly limited, but is preferably 0.01 to 5 parts by weight, more preferably 0.05 to 3 parts by weight, and still more preferably 0.1 to 1.5 parts by weight with respect to 100 parts by weight of P3HA. Further, the lubricant may be used alone or in combination of two or more, and the mixing ratio can be appropriately adjusted according to the purpose.

[0041] Examples of the plasticizer include glycerin ester compounds, citrate compounds, sebacate compounds, adipate compounds, polyether ester compounds, benzoate compounds, phthalate compounds, isosorbide ester compounds, polycaprolactone compounds, dibasic acid ester compounds, and the like. Among them, glycerin ester compounds, citrate compounds, sebacate compounds, and dibasic acid ester compounds are preferable in that the plasticizing effect on P3HA is particularly excellent. Examples of the glycerin ester compound include glycerin diacetomonolaurate and the like. Examples of the citrate compound include tributyl acetylcitrate and the like. Examples of the sebacate compound include dibutyl sebacate and the like. Examples of the dibasic acid ester compound include benzylmethyl diethylene glycol adipate and the like. The amount of the plasticizer used is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and still more preferably 3 to 10 parts by weight with respect to 100 parts by weight of P3HA. Further, the plasticizer may be used alone or in combination of two or more, and the mixing ratio can be appropriately adjusted according to the purpose.

[0042] Examples of the colorant include organic pigments such as azo-based, polycondensed azo-based, azo-based containing an azomethine group, azomethine-based, anthraquinone-based, phthalocyanine-based, perinone·perylene-based, indigo·thioindigo-based, dioxazine-based, quinacridone-based, isoindolinone-based, diketopyrrolopyrrole-based, quinophthalone-based, etc., and inorganic pigments such as iron oxide-based pigments, iron hydroxide-based pigments, ultramarine-based pigments, carbon black-based pigments, titanium oxide-based pigments, composite oxide-based pigments, etc. The amount of the colorant used is not particularly limited, but is preferably 0.001 to 5 parts by weight, more preferably 0.05 to 5 parts by weight, and still more preferably 0.1 to 2 parts by weight with respect to 100 parts by weight of P3HA. Further, not only one kind but also two or more kinds of the colorants may be mixed, and the mixing ratio can be appropriately adjusted according to the purpose.

[0043] When producing resin particles composed of a P3HA-based composition, it is also possible to use a compound having an isocyanate group (hereinafter referred to as an isocyanate compound). However, the isocyanate compound may be toxic. Further, the obtained P3HA-based foamed particles or foamed molded article may turn yellow. Therefore, the amount of the isocyanate compound used is preferably less than 3 parts by weight, more preferably less than 1 part by weight, and still more preferably less than 0.1 part by weight with respect to 100 parts by weight of P3HA. Most preferably, the resin particles do not contain an isocyanate compound.

[0044] As the isocyanate compound, for example, a polyisocyanate compound having two or more isocyanate groups in one molecule can be used. Specific types include aromatic, alicyclic, and aliphatic isocyanates. For example, as aromatic isocyanates, there are isocyanate compounds having a tolylene, diphenylmethane, naphthylene, tolidine, xylene, or triphenylmethane skeleton; as alicyclic isocyanates, there are isocyanate compounds having an isophorone or hydrogenated diphenylmethane skeleton; and as aliphatic isocyanates, there are isocyanate compounds having a hexamethylene or lysine skeleton. Furthermore, a combination of two or more of these isocyanate compounds can also be used, but from the viewpoints of versatility, handleability, weather resistance, etc., the use of tolylene, diphenylmethane, particularly the polyisocyanate of diphenylmethane, is preferred.

[0045] The resin particles composed of the P3HA-based composition (similarly for P3HA-based foamed particles) may or may not substantially contain a resin component other than P3HA (which may be referred to as "other resin component"). Examples of other resin components include aliphatic polyesters and aliphatic aromatic polyesters such as polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone. Note that the other resin component can be used alone or in combination of two or more. The content of the other resin component in the resin particles composed of the P3HA-based composition (similarly for P3HA-based foamed particles) is not particularly limited, but for example, 10 to 400 parts by weight, more preferably 50 to 150 parts by weight, is preferred with respect to 100 parts by weight of P3HA.

[0046] The method for producing resin particles composed of a P3HA-based composition is not particularly limited and can be produced by applying known or conventional methods. For example, first, the P3HA and, if necessary, the additive are melt-kneaded using an extruder, kneader, Banbury mixer, roll, etc., and the molten P3HA-based composition is discharged from the nozzle of a die, cooled, and then cut to obtain resin particles in a shape such as cylindrical, elliptical cylindrical, spherical, cubic, rectangular parallelepiped, etc., which are easy to use for foaming. As the production apparatus, a twin-screw extruder is preferred from the viewpoints of productivity and convenience.

[0047] In the method for producing resin particles composed of the P3HA-based composition, the temperature for melt-kneading the P3HA and, if necessary, the additive cannot be generally specified because it depends on the melting point, weight-average molecular weight, etc. of the P3HA and also on the additive used. However, for example, it is preferable that the temperature of the molten P3HA-based composition discharged from the nozzle of the die is 150 to 200°C, more preferably 160 to 195°C, and still more preferably 170 to 190°C. When the temperature of the molten P3HA-based composition is less than 150°C, the P3HA-based composition tends to be insufficiently melt-kneaded. On the other hand, when the temperature of the molten P3HA-based composition exceeds 200°C, the P3HA tends to be easily thermally decomposed.

[0048] In the method for producing resin particles composed of the P3HA-based composition, the temperature for cooling the molten P3HA-based composition discharged from the nozzle of the die is not particularly limited, but is preferably 20 to 80°C, more preferably 30 to 70°C, and still more preferably 40 to 60°C. When the cooling temperature is 20°C or higher, the crystallization of the molten P3HA-based composition becomes faster, and the productivity of the resin particles composed of the P3HA-based composition tends to be better. On the other hand, when the cooling temperature is 80°C or lower, the crystallization of the molten P3HA-based composition becomes faster, and the productivity of the resin particles composed of the P3HA-based composition tends to be better.

[0049] [P3HA-based foamed particles] The P3HA-based foamed particles according to this embodiment can be obtained by foaming resin particles composed of the above-described P3HA-based composition using a foaming agent.

[0050] The gel fraction exhibited by the P3HA-based foamed particles is an index indicating the degree of crosslinking of P3HA in the foamed particles. Although the gel fraction is not particularly limited, it is preferably in the range of 20 to 90% by weight. Also, the gel fraction may exceed 75% by weight, for example, it may be 76% by weight or more. Further, it may exceed 80% by weight, for example, it may be 81% by weight or more. The gel fraction of the P3HA-based foamed particles can be controlled by the type and amount of the crosslinking agent used, etc., which will be described later.

[0051] The method for measuring the gel fraction of the P3HA-based foamed particles is as follows. Put 0.5 g of the foamed particles and 50 ml of chloroform into a 100 ml flask, heat and reflux at 62 °C for 8 hours under atmospheric pressure, and then filter the obtained heat-treated product using a suction filtration device having a 100-mesh wire mesh. The filtered product on the obtained wire mesh is dried in an oven at 80 °C under vacuum conditions for 8 hours. At this time, measure the weight Wgw (g) of the obtained dried product. The gel fraction is calculated as Wgw / 0.5 × 100 (% by weight).

[0052] The weight per particle of the P3HA-based foamed particles is preferably 0.3 to 10 mg, more preferably 0.4 to 7.5 mg, and even more preferably 0.5 to 5 mg. When the weight per particle is 0.3 mg or more, resin particles composed of the P3HA-based composition can be stably produced with high productivity, so the uniformity of the obtained P3HA-based foamed particles tends to increase. On the other hand, when the weight per particle is 10 mg or less, thinning of the P3HA-based foam-molded article can be easily realized.

[0053] When the shape of the P3HA-based foamed particles is cylindrical, the length / diameter of the foamed particles is preferably 0.5 to 2.5, more preferably 0.7 to 1.5, and still more preferably 0.8 to 1.2. If the length / diameter is less than 0.5, the surface property of the foamed molded body tends to deteriorate. If the length / diameter exceeds 2.5, the filling property during in-mold foaming molding tends to deteriorate.

[0054] The apparent density of the P3HA-based foamed particles is not particularly limited, but is preferably 20 to 150 g / L, more preferably 23 to 140 g / L, and still more preferably 25 to 130 g / L. When P3HA-based foamed particles having a desired apparent density cannot be obtained by only one foaming, the once-foamed foamed particles may be subjected to the second and subsequent foaming steps. The apparent density of the P3HA-based foamed particles is measured as follows. Prepare a graduated cylinder containing ethanol, sink a group of foamed particles with a weight Wd (g) into the graduated cylinder using a wire mesh or the like, and let the volume of the group of foamed particles read from the rise in the ethanol water level be Vd (L). The apparent density of the foamed particles is Wd / Vd (g / L).

[0055] The closed-cell ratio of the P3HA-based foamed particles is not particularly limited, but is preferably 88% or more, more preferably 90% or more, and still more preferably 93% or more. If the closed-cell ratio is less than 88%, the molding shrinkage rate of the obtained foamed molded body tends to increase. The method for measuring the closed-cell ratio of the P3HA-based foamed particles is as follows. For the P3HA-based foamed particles, in accordance with the method described in Procedure C of ASTM D2856-87, using an air comparison pycnometer (Model 1000 manufactured by Tokyo Science Co., Ltd.), measure the volume Vc (cm 3 ). Next, sink the total amount of the foamed particles after measuring Vc into a graduated cylinder containing ethanol, and obtain the apparent volume Va (cm 3 ) of the foamed particles from the rise in the water level of the graduated cylinder (water immersion method). The closed-cell ratio of the foamed particles is 100 - (Va - Vc) × 100 / Va (%).

[0056] The average bubble diameter of the P3HA-based foamed particles is not particularly limited, but is preferably 50 to 500 μm, more preferably 100 to 400 μm. The method for measuring the average bubble diameter of the P3HA-based foamed particles is as follows. The foamed particles are cut at the center of the foamed particles using a razor (High Stainless Double-Edge Blade manufactured by Feather). In the image obtained by observing the cut surface at a magnification of 50 times using an optical microscope (VHX-100 manufactured by Keyence), a straight line passing through approximately the center of the foamed particles is drawn, and the number of bubbles n penetrated by the straight line and the foamed particle diameter L (μm) determined from the intersection of the straight line and the surface of the foamed particles are read. The average bubble diameter of the foamed particles is L / n (μm).

[0057] The P3HA-based foamed particles can be produced by the method described below. First, a blowing agent is introduced into a pressure-resistant container containing an aqueous dispersion containing resin particles composed of a P3HA-based composition, water, and a cross-linking agent, and optionally a dispersant, a dispersion aid, a cross-linking aid, and / or a plasticizer. More specifically, resin particles composed of a P3HA-based composition, water, and a cross-linking agent, and optionally a dispersant, a dispersion aid, a cross-linking aid, and / or a plasticizer are charged into a pressure-resistant container under stirring, and these are sufficiently dispersed to form an aqueous dispersion, and then the blowing agent may be introduced into the pressure-resistant container. Alternatively, after sufficiently dispersing resin particles composed of a P3HA-based composition, water, and a cross-linking agent, and optionally a dispersant, a dispersion aid, a cross-linking aid, and / or a plasticizer in a separate container, the obtained dispersion and the blowing agent may be sequentially introduced into the pressure-resistant container.

[0058] Next, the content of the pressure-resistant container is heated to a predetermined temperature (foaming temperature) within the range of 130 to 150 °C and held at this predetermined temperature for 5 to 55 minutes. By doing so, while softening the resin particles, the resin particles can be impregnated with a foaming agent, and the resin particles can also be impregnated with and reacted with a crosslinking agent. In this embodiment, since a mixture of a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer is used as P3HA, a high foaming temperature can be adopted, and accordingly, by setting the holding time short, the productivity of the foamed particles can be increased. In addition, even though the holding time is short, it is possible to suppress the odor of the foamed particles by using an organic peroxide of percarbonates as the crosslinking agent.

[0059] After holding at the predetermined temperature, one end of the pressure-resistant container is released, and the content of the pressure-resistant container containing resin particles and water is discharged into an atmosphere at a pressure lower than the pressure inside the pressure-resistant container, thereby foaming the resin particles to obtain P3HA-based foamed particles (this series of operations may be referred to as pressure release foaming hereinafter). Note that the temperature inside the pressure-resistant container when discharging into the low-pressure atmosphere is defined as the foaming temperature, and the pressure inside the pressure-resistant container when discharging into the low-pressure atmosphere is defined as the foaming pressure.

[0060] The water may be any water that can uniformly disperse resin particles, a dispersant, a dispersion aid, a crosslinking agent, a foaming agent, etc. composed of the P3HA-based composition, and is not particularly limited. For example, pure water and ultrapure water such as RO water (water purified by the reverse osmosis membrane method), distilled water, and deionized water (water purified by an ion exchange resin) can be used. The amount of water used is not particularly limited, but is preferably 100 to 1000 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition.

[0061] Examples of the dispersant include inorganic substances such as tricalcium phosphate, magnesium phosphate, basic magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, aluminum oxide, titanium oxide, and aluminum hydroxide. The amount of the dispersant used is not particularly limited, but is preferably 0.1 to 3.0 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition.

[0062] Examples of the dispersion aid include anionic surfactants such as sodium dodecylbenzenesulfonate, sodium α-olefinsulfonate, and sodium normal paraffinsulfonate. The amount of the dispersion aid used is not particularly limited, but is preferably 0.001 to 0.5 parts by weight, more preferably 0.01 to 0.2 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition.

[0063] As the crosslinking agent, organic peroxides of percarbonates are used. Since the organic peroxide does not need to be mixed and reacted with P3HA by melt kneading and can be impregnated and reacted with the resin particles after the resin particles are prepared as described above, it is a crosslinking agent that is preferable in terms of process. By using an organic peroxide as the crosslinking agent, the molecular chains of P3HA are directly bonded to form a crosslinked structure without an intervening structure derived from the crosslinking agent. Furthermore, by using an organic peroxide of percarbonates, the odor of the foamed particles can be suppressed.

[0064] The crosslinking agent desirably has characteristics such as the crosslinking reaction proceeding near the softening temperature of the resin particles, good compatibility with P3HA, and being easily impregnated into the interior of the resin particles. From this perspective, the organic peroxide of the percarbonates is preferably an organic peroxide having a half-life temperature of 150 to 170°C for 1 minute and being liquid at room temperature. Among them, since the half-life temperature for 1 minute can be satisfied, an organic peroxide having one carbonate group is preferred. Further, in order to avoid the odor derived from aromatic compounds, the organic peroxide of the percarbonates is preferably a compound having no aromatic ring. Specifically, t-butylperoxy-2-ethylhexyl monocarbonate (half-life temperature for 1 minute: 161°C), t-butylperoxyisopropyl monocarbonate (half-life temperature for 1 minute: 159°C), t-amylperoxy-2-ethylhexyl monocarbonate (half-life temperature for 1 minute: 155°C), t-amylperoxyisopropyl monocarbonate (half-life temperature for 1 minute: 153°C), etc. may be mentioned. These crosslinking agents may be used alone or in combination of two or more.

[0065] The amount of the crosslinking agent used is not particularly limited, but is preferably 1.2 to 5 parts by weight, more preferably 1.3 to 4 parts by weight, still more preferably 1.4 to 3.5 parts by weight, and particularly preferably 1.5 to 3 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition. If the amount of the crosslinking agent used is less than 1.2 parts by weight, the gel fraction shown by the P3HA-based foamed particles will not be sufficiently high, and it will be difficult to perform in-mold foaming molding from the foamed particles to the foamed molded body. Also, even if molding is possible, the range of molding processing conditions that can be adopted when performing in-mold foaming molding on the foamed molded body becomes narrow. On the other hand, if the amount of the crosslinking agent used exceeds 5 parts by weight, not only the added effect cannot be obtained, but it tends to be economically wasted. The amount of the crosslinking agent used has a correlation with the gel fraction of the P3HA-based foamed particles and affects the value of the gel fraction. Therefore, it is desirable to set the amount of the crosslinking agent used in consideration of the obtained value of the gel fraction.

[0066] Examples of the crosslinking aid include compounds having at least one unsaturated bond in the molecule. Among them, allyl esters, acrylic esters, methacrylic esters, divinyl compounds, etc. are particularly preferable. The amount of the crosslinking aid used is not particularly limited, but is preferably 0.01 to 3 parts by weight, more preferably 0.03 to 1.5 parts by weight, and still more preferably 0.05 to 1 part by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition. However, the crosslinking aid may not be used.

[0067] Examples of the plasticizer include glycerin ester compounds, citric acid ester compounds, sebacic acid ester compounds, adipic acid ester compounds, polyether ester compounds, benzoic acid ester compounds, phthalic acid ester compounds, isosorbide ester compounds, polycaprolactone compounds, dibasic acid ester compounds, etc. Among them, glycerin ester compounds, citric acid ester compounds, sebacic acid ester compounds, and dibasic acid ester compounds are preferable in terms of excellent plasticizing effect on P3HA. Examples of the glycerin ester compound include glycerin diacetomonolaurate. Examples of the citric acid ester compound include tributyl acetylcitrate. Examples of the sebacic acid ester compound include dibutyl sebacate. Examples of the dibasic acid ester compound include benzylmethyl diethylene glycol adipate. The amount of the plasticizer used is not particularly limited, but is preferably 1 to 20 parts by weight, more preferably 2 to 15 parts by weight, and still more preferably 3 to 10 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition. However, the plasticizer may not be used. Further, the plasticizer may be used alone or in a mixture of two or more, and the mixing ratio can be appropriately adjusted according to the purpose.

[0068] Examples of the foaming agent include inorganic gases such as carbon dioxide, nitrogen, and air; saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane; ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane; water; etc. At least one selected from these groups can be used. Among them, it is preferable to use carbon dioxide from the viewpoints of environmental load and foaming power. The addition amount of the foaming agent is not particularly limited, but is preferably 2 to 10,000 parts by weight, more preferably 5 to 5,000 parts by weight, and still more preferably 10 to 1,000 parts by weight with respect to 100 parts by weight of the resin particles composed of the P3HA-based composition. When the addition amount of the foaming agent is less than 2 parts by weight, it tends to be difficult to obtain foamed particles with a low apparent density. On the other hand, when the addition amount of the foaming agent exceeds 10,000 parts by weight, the added effect cannot be obtained and it tends to be economically wasteful.

[0069] In the pressure-relief foaming, when impregnating and reacting the resin particles composed of the P3HA-based composition with a crosslinking agent and, if necessary, a crosslinking aid, it is preferable to lower the oxygen concentration in the pressure-resistant container and the dissolved oxygen amount of water in order to increase the crosslinking efficiency. Examples of the method include substitution with an inorganic gas such as carbon dioxide or nitrogen, and evacuation.

[0070] In the pressure-relief foaming, the rate of temperature increase (hereinafter sometimes referred to as the heating rate) when raising the temperature to the desired foaming temperature is preferably 1 to 3 °C / min, more preferably 1.5 to 3 °C / min. When the heating rate is 1 °C / min or more, the productivity tends to be good. On the other hand, when the heating rate is 3 °C / min or less, the impregnation of the foaming agent into the resin particles composed of the P3HA-based composition and the impregnation and reaction of the crosslinking agent can proceed sufficiently during the temperature increase.

[0071] In the pressure-relief foaming, the predetermined temperature (foaming temperature) is in the range of 130 to 150°C as described above. If the predetermined temperature is less than 130°C, the impregnation of the blowing agent into the resin particles composed of the P3HA-based composition containing the poly(3-hydroxyalkanoate) copolymer and the poly(3-hydroxybutyrate) homopolymer becomes insufficient, and the resin particles may not foam, making it difficult to obtain foamed particles. On the other hand, if the predetermined temperature exceeds 150°C, the hydrolysis of P3HA may proceed. The predetermined temperature is preferably 132 to 148°C, more preferably 134 to 146°C, and even more preferably 136 to 144°C. Also, the predetermined temperature may exceed 140°C, for example, it may be 141°C or higher.

[0072] In the pressure-relief foaming, the foaming pressure (i.e., the pressure inside the pressure-resistant container) is preferably 1 to 10 MPa (gauge pressure), more preferably 2 to 5 MPa (gauge pressure). When the foaming pressure is less than 1 MPa (gauge pressure), it tends to be difficult to obtain foamed particles with a low apparent density.

[0073] In the pressure-relief foaming, the time for holding the contents of the pressure-resistant container at the predetermined temperature is 5 to 55 minutes as described above. If the holding time is less than 5 minutes, unreacted cross-linking agent may remain in the resin particles. On the other hand, if it exceeds 55 minutes, the productivity of the foamed particles becomes insufficient. The holding time is preferably 10 to 50 minutes, more preferably 15 to 40 minutes, and even more preferably 20 to 35 minutes.

[0074] In the pressure-relief foaming, when discharging the contents in the pressure-resistant container into a low-pressure atmosphere, for the purposes of flow rate adjustment and reduction of foaming ratio variation, etc., it can also be discharged through an opening orifice with a diameter of 1 to 5 mm. Also, for resin particles composed of a P3HA-based composition with a relatively high melting point, for the purpose of improving the foamability, the low-pressure atmosphere may be filled with saturated water vapor.

[0075] If the pressure-relief foaming is carried out only once, P3HA-based foamed particles with a desired apparent density may not be obtained. In that case, the P3HA-based foamed particles obtained by the pressure-relief foaming are put into a pressure-resistant container, and the pressure inside the P3HA-based foamed particles (hereinafter sometimes referred to as the internal pressure of the foamed particles) is made higher than the normal pressure by a pressurization treatment of impregnating with an inorganic gas such as air or carbon dioxide. Then, the P3HA-based foamed particles are heated with superheated steam or the like to further expand, and they may be used as P3HA-based double-foamed particles with a desired apparent density (hereinafter, this series of operations may sometimes be referred to as double foaming).

[0076] When performing the double foaming, the internal pressure of the foamed particles is preferably 0.15 to 0.60 MPa (absolute pressure), more preferably 0.20 to 0.50 MPa (absolute pressure).

[0077] In the double foaming, the temperature inside the pressure-resistant container when impregnating the P3HA-based foamed particles with an inorganic gas is preferably 10 to 90 °C, more preferably 40 to 90 °C.

[0078] In the double foaming, the pressure of superheated steam or the like for heating the P3HA-based foamed particles (hereinafter sometimes referred to as the double foaming pressure) varies depending on the characteristics of the foamed particles used and the desired apparent density, and cannot be generally specified. However, it is preferably 0.01 to 0.17 MPa (gauge pressure), more preferably 0.01 to 0.10 MPa (gauge pressure).

[0079] The P3HA-based double-foamed particles preferably satisfy the apparent density, closed-cell ratio, and average cell diameter of the above-mentioned P3HA-based foamed particles.

[0080] [P3HA-based foamed molded article] The manufacturing method of the P3HA-based foamed molded article is not particularly limited, and the P3HA-based foamed particles (including the above-mentioned P3HA-based double-foamed particles, the same hereinafter) may be heated and molded in a mold, and known or conventional methods can be applied. For example, the following methods (A) to (D) of in-mold foaming molding and the like can be mentioned, but it is not particularly limited.

[0081] (A) A method of pressurizing P3HA-based expanded particles with an inorganic gas to impregnate the expanded particles with the inorganic gas, applying a predetermined internal pressure of the expanded particles, filling the expanded particles into a mold, and heating with superheated steam (B) A method of filling P3HA-based expanded particles into a mold, then compressing the volume inside the mold by 10 to 75%, and heating with superheated steam (C) A method of compressing P3HA-based expanded particles with gas pressure, filling them into a mold, and heating with superheated steam by utilizing the resilience of the expanded particles (D) A method of filling P3HA-based expanded particles into a mold and heating with superheated steam without any particular pretreatment

[0082] In the production of a P3HA-based foamed molded article, the pressure of the superheated steam for heating the P3HA-based expanded particles (hereinafter sometimes referred to as the molding pressure) varies depending on the characteristics of the expanded particles used and the like, and cannot be generally specified, but is preferably 0.05 to 0.30 MPa (gauge pressure), more preferably 0.08 to 0.25 MPa (gauge pressure).

[0083] As the inorganic gas in the method (A) among the production methods of P3HA-based foamed molded articles, air, nitrogen, oxygen, carbon dioxide, helium, neon, argon, etc. can be used, and at least one selected from these groups can be used. Among these, air or carbon dioxide is preferred.

[0084] In the method (A) among the production methods of P3HA-based foamed molded articles, the internal pressure of the expanded particles is preferably 0.10 to 0.30 MPa (absolute pressure), more preferably 0.11 to 0.25 MPa (absolute pressure).

[0085] As the temperature inside the pressure-resistant container when impregnating the P3HA-based expanded particles with the inorganic gas in the method (A) among the production methods of P3HA-based foamed molded articles, 10 to 90 °C is preferred, more preferably 40 to 90 °C.

[0086] The P3HA-based foamed molded article can be used for various applications, for example, it can be used for applications such as packaging cushioning materials, agricultural product boxes, fish boxes, automobile parts, building materials, and civil engineering materials.

Example

[0087] Hereinafter, the present invention will be specifically described by way of examples. However, the technical scope of the present invention is not limited by these examples.

[0088] The substances used in the examples and comparative examples are shown below. [Poly(3-hydroxyalkanoate)] P3HA-1: A mixture of P3HB3HH and P3HB (weight ratio 92:8) (the monomer ratio in P3HB3HH is 3HB / 3HH = 95 / 5 (mol% / mol%)) P3HA-2: A mixture of P3HB3HH and P3HB (weight ratio 96:4) (the monomer ratio in P3HB3HH is 3HB / 3HH = 95 / 5 (mol% / mol%)) P3HA-3: 100% by weight of P3HB3HH (the monomer ratio in P3HB3HH is 3HB / 3HH = 95 / 5 (mol% / mol%))

[0089] [Bubble regulator] Bubble regulator: Talc (Talkan Powder PK-S manufactured by Hayashi Kasei Co., Ltd.)

[0090] [Dispersant] Dispersant: Calcium phosphate tribasic (manufactured by Taihei Chemical Industry Co., Ltd.)

[0091] [Dispersion aid] Dispersion aid: Sodium alkyl sulfonate (Latemul PS manufactured by Kao Corporation)

[0092] [Crosslinking agent] Crosslinking agent - 1: t-Butyl peroxy-2-ethylhexyl carbonate (content 97%) (Perbutyl E manufactured by NOF Corporation) Crosslinking agent - 2: Benzoyl peroxide (content 75%) (Niper BW manufactured by NOF Corporation)

[0093] The evaluation methods carried out in the examples and comparative examples will be described below.

[0094] [Measurement of the melting point of resin particles composed of P3HA-based compositions] Using a differential scanning calorimeter (DSC7020 manufactured by Hitachi High-Technologies Corporation), approximately 5 mg of resin particles composed of the P3HA-based composition was weighed, and in the DSC curve obtained when the temperature was raised from 10°C to 190°C at a heating rate of 10°C / min, the temperature of the highest melting peak was defined as the melting point (see Figure 1).

[0095] [Measurement of MFR of Resin Particles Composed of P3HA-Based Composition] Using a melt flow index tester (manufactured by Yasuda Seiki Seisakusho), in accordance with JIS K7210, the measurement was carried out under the conditions of a load of 5 kg and a measurement temperature of the end temperature of melting read from the DSC curve obtained in "Measurement of Melting Point of Resin Particles Composed of P3HA-Based Composition" + 1 to 10°C.

[0096] [Evaluation of Productivity of P3HA-Based Expanded Particles] The productivity of the P3HA-based expanded particles was evaluated according to the following criteria. ◎: In the production of P3HA-based expanded particles, the time from the start of temperature rise to the start of foaming is within 55 minutes, and the productivity is very high. ○: In the production of P3HA-based expanded particles, the time from the start of temperature rise to the start of foaming is between 56 minutes and 70 minutes, and the productivity is high. ×: In the production of P3HA-based expanded particles, the time from the start of temperature rise to the start of foaming is between 71 minutes and 100 minutes, and the productivity is poor. ××: In the production of P3HA-based expanded particles, the time from the start of temperature rise to the start of foaming exceeds 100 minutes, and the productivity is very poor, or no expanded particles can be obtained.

[0097] [Evaluation of Odor of P3HA-Based Expanded Particles] A sensory test was conducted by 10 persons engaged in the handling of the crosslinking agent, and the odor derived from the crosslinking agent or its decomposition product that the P3HA-based expanded particles may emit was evaluated according to the following criteria. ○: All 10 sensory testers determined that the P3HA-based expanded particles had no odor. △: One or more but nine or fewer of the sensory testers determined that the P3HA-based expanded particles had an odor. ×: All 10 sensory testers determined that the P3HA-based foamed particles had an odor. ××: All 10 sensory testers determined that the P3HA-based foamed particles had an odor derived from aromatic compounds.

[0098] [Measurement of Gel Fraction of P3HA-Based Foamed Particles] Into a 100 ml flask, 0.5 g of P3HA-based foamed particles and 50 ml of chloroform were placed, and after heating under reflux at 62 °C for 8 hours under atmospheric pressure, the obtained heat-treated product was filtered using a suction filtration device having a 100-mesh wire mesh. The filtered product on the wire mesh was dried in an oven at 80 °C under vacuum conditions for 8 hours. At this time, the weight Wgw (g) of the obtained dried product was measured. The gel fraction was determined from Wgw / 0.5 × 100 (wt%).

[0099] [Measurement of Apparent Density of P3HA-Based Foamed Particles or P3HA-Based Two-Stage Foamed Particles] A graduated cylinder filled with ethanol was prepared, and P3HA-based foamed particles or P3HA-based two-stage foamed particles (the weight Wd (g) of the foamed particles) were submerged in the graduated cylinder using a wire mesh or the like, and the volume of the foamed particles read from the rise in the ethanol water level was taken as Vd (L). The apparent density of the foamed particles was determined from Wd / Vd (g / L).

[0100] [Measurement of Density of P3HA-Based Foamed Molding] The length, width, and thickness of the P3HA-based foamed molding were measured with a digital vernier caliper, and the volume of the foamed molding was determined. The value obtained by dividing the weight of the foamed molding by the volume of the foamed molding was taken as the density of the foamed molding.

[0101] <Example 1> [Production of Resin Particles Composed of P3HA-Based Composition] Using P3HA-1 as the P3HA, it was weighed so that P3HA-1 was 100 parts by weight and the bubble regulator was 0.1 part by weight, and dry blended. The dry blended mixture was melt kneaded at a cylinder set temperature of 140 to 170 °C using a twin screw extruder (TEM-26SX manufactured by Toshiba Machine Co., Ltd.), and the molten P3HA-based composition at 185 °C discharged from the nozzle of the die attached to the tip of the extruder was water-cooled at 43 °C and then cut to obtain resin particles with a weight of 2.0 mg per granule. The obtained resin particles had a melting point of 163 °C and an MFR measured at 170 °C of 2.5 g / 10 min.

[0102] [Production of P3HA-based foamed particles] 100 parts by weight of the obtained resin particles, 200 parts by weight of pure water, 1.0 part by weight of a dispersant, 0.1 part by weight of a dispersion aid, and 2 parts by weight of a crosslinking agent were charged into a pressure-resistant container under stirring, and then degassed to remove oxygen in the pressure-resistant container. Next, carbon dioxide was introduced into the pressure-resistant container as a foaming agent. Thereafter, the temperature of the contents of the pressure-resistant container was raised to a foaming temperature of 142.0 °C over 40 minutes. Thereafter, carbon dioxide was additionally introduced to increase the pressure to a foaming pressure of 3.3 MPa (gauge pressure), and it was held for 30 minutes near the foaming temperature and near the foaming pressure. Thereafter, the valve at the bottom of the pressure-resistant container was opened, and the contents of the pressure-resistant container were discharged to atmospheric pressure through an opening orifice with a diameter of 3.6 mm to obtain foamed particles. The time from the start of temperature rise to the start of foaming was 70 minutes, and the productivity of the foamed particles was high. After washing the dispersant adhering to the surface of the foamed particles, it was dried at 90 °C. The odor emitted from the obtained foamed particles was judged to be absent by all 10 sensory testers. The characteristics of other foamed particles are summarized in Table 1.

[0103]

Table 1

[0104] [Production of P3HA-based foamed molded article] The obtained foamed particles were charged into a pressure-resistant container heated to 80 °C, and the internal pressure of the foamed particles was set to 0.18 MPa (absolute pressure) by pressurizing with air. The foamed particles were filled into a mold with dimensions of 370 mm in length × 320 mm in width × 60 mm in thickness of a molding machine (EP-900L-M5 manufactured by DAISEN Co., Ltd.). Next, it was heated with superheated steam at a pressure of 0.15 MPa (gauge pressure) to obtain a foamed molded body, and then dried at 75 °C. The density of the obtained foamed molded body was 48 g / L.

[0105] <Examples 2, 3, Comparative Examples 1 to 5> Resin particles, foamed particles, and foamed molded bodies were produced in the same manner as in Example 1 except that the formulation and foaming conditions were changed as shown in Table 1, and the same evaluation as in Example 1 was carried out. The results were summarized in Table 1.

[0106] As shown in Table 1, as the poly(3-hydroxyalkanoate), a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer in a weight ratio of 99:1 to 80:20 was used, and an organic peroxide of percarbonates was used as the cross-linking agent. In Examples 1 to 3 where the foaming temperature was in the range of 130 to 150 °C, the productivity of the P3HA-based foamed particles was high, and the odor emitted by the obtained foamed particles was suppressed.

[0107] On the other hand, in Comparative Examples 1 and 2 where only a poly(3-hydroxyalkanoate) copolymer was used as the poly(3-hydroxyalkanoate) and the foaming temperature was not in the range of 130 to 150 °C, although foamed particles were obtained, it was difficult to achieve both high productivity of the foamed particles and suppression of the odor emitted by the foamed particles. That is, in Comparative Example 1, the odor was suppressed, but the productivity was poor, and in Comparative Example 2 where the holding time was shortened, the productivity was high, but there was an odor.

[0108] In Comparative Example 3, the foaming temperature was in the range of 130 to 150 °C, but since only a poly(3-hydroxyalkanoate) copolymer was used as the poly(3-hydroxyalkanoate), the resin particles made of the poly(3-hydroxyalkanoate) copolymer became lumps in the pressure-resistant container and could not even be foamed.

[0109] In Comparative Example 4, a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer was used as the poly(3-hydroxyalkanoate). However, since the foaming temperature was not in the range of 130 to 150°C, it was not even possible to obtain foamed particles.

[0110] In Comparative Example 5, a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer was used as the poly(3-hydroxyalkanoate). However, since benzoyl peroxide was used instead of percarbonates as the crosslinking agent, the obtained foamed particles had an odor derived from aromatic compounds.

[0111] <Example 4> [Production of P3HA-based two-stage foamed particles and foamed molded article] The foamed particles obtained in Example 1 were charged into a pressure-resistant container heated to 80°C, and the internal pressure of the foamed particles was set to 0.30 MPa (absolute pressure) by pressurizing with air. Then, it was heated with superheated steam at a pressure of 0.04 MPa (gauge pressure) to obtain two-stage foamed particles, which were then dried at 75°C. The odor emitted by the obtained two-stage foamed particles was judged to be absent by all 10 sensory testers.

[0112] The obtained two-stage foamed particles were charged into a pressure-resistant container heated to 80°C, and the internal pressure of the foamed particles was set to 0.18 MPa (absolute pressure) by pressurizing with air. The foamed particles were filled into a mold with a length of 370 mm, a width of 320 mm, and a thickness of 60 mm of a molding machine (EP-900 manufactured by DAISEN Co., Ltd.). Next, it was heated with superheated steam at a pressure of 0.15 MPa (gauge pressure) to obtain a foamed molded article, which was then dried at 75°C. The density of the obtained foamed molded article was 25 g / L.

[0113] As described above, it was confirmed that according to the production method of the present invention, poly(3-hydroxyalkanoate)-based foamed particles and foamed molded articles with high productivity and suppressed odor can be produced.

Claims

1. A method for producing poly(3-hydroxyalkanoate) foam particles, comprising: introducing a blowing agent into an aqueous dispersion containing resin particles containing poly(3-hydroxyalkanoate) and a crosslinking agent in a pressure-resistant container; heating the contents of the pressure-resistant container to a predetermined temperature within the range of 130 to 150 °C and holding at the predetermined temperature for 5 to 55 minutes; and foaming the resin particles by opening one end of the pressure-resistant container and discharging the contents of the pressure-resistant container into a low-pressure atmosphere, wherein the poly(3-hydroxyalkanoate) is a mixture containing a poly(3-hydroxyalkanoate) copolymer and a poly(3-hydroxybutyrate) homopolymer in a weight ratio of 99:1 to 80:20, and the crosslinking agent is an organic peroxide of percarbonates.

2. The method for producing poly(3-hydroxyalkanoate) foam particles according to Claim 1, wherein the blowing agent is carbon dioxide.

3. The method for producing poly(3-hydroxyalkanoate) foam particles according to Claim 1 or 2, wherein the poly(3-hydroxyalkanoate) copolymer is a copolymer of 3-hydroxybutyrate and a comonomer, and the monomer ratio in the copolymer is 3-hydroxybutyrate / comonomer = 99 / 1 to 89 / 11 (mol% / mol%).

4. The method for producing poly(3-hydroxyalkanoate) foam particles according to any one of Claims 1 to 3, wherein the organic peroxide of percarbonates has a half-life temperature of 150 to 170 °C in 1 minute and is liquid at room temperature.

5. The method for producing poly(3-hydroxyalkanoate) foam particles according to Claim 4, wherein the organic peroxide of percarbonates is a compound having one carbonate group.

6. The method for producing poly(3-hydroxyalkanoate) foam particles according to any one of Claims 1 to 5, further comprising impregnating the obtained foam particles with an inorganic gas to increase the pressure inside the foam particles, and then heating and expanding the foam particles.

7. A method for producing a poly(3-hydroxyalkanoate) foam molded article, comprising: producing poly(3-hydroxyalkanoate) foam particles by the production method according to any one of Claims 1 to 6, and heating and molding the foam particles in a mold.

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