Aliphatic polyester-based foamed particles and method for producing aliphatic polyester-based foamed molded body

Abstract

To provide a novel method for producing aliphatic polyester-based foamed particles, capable of providing foamed particles that suppress adhesion between foamed particles during foaming and allow production of a foamed molded body having superior fusibility.SOLUTION: A method for producing foamed particles comprises: a step (A) of obtaining foamed particles by foaming resin particles in the presence of a dispersant; and a step (B) of washing the foamed particles under specific conditions using a washing solution containing a specific water-soluble compound at a specific concentration.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a method for producing expanded aliphatic polyester beads and a method for producing an expanded aliphatic polyester molded article. [Background technology]

[0002] Conventionally, there is known a technique for producing expanded beads by expanding resin beads made of a thermoplastic resin. Also, there is known a technique for using a dispersant when expanding the resin beads to prevent the resin beads from adhering to each other during expansion (Patent Documents 1 and 2).

[0003] In recent years, from the viewpoint of environmental consideration, biodegradable thermoplastic resins such as aliphatic polyester resins have been used in place of conventional thermoplastic resins such as polyolefins. For example, Patent Document 3 discloses a technique for producing expanded beads using a PHA resin, which is a type of aliphatic polyester resin. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent Publication No. 2000-290419 [Patent Document 2] Japanese Patent Application Publication No. 10-120819 [Patent Document 3] International Publication No. WO2022 / 230746 Summary of the Invention [Problem to be solved by the invention]

[0005] In the course of their research into expanded aliphatic polyester particles obtained by expanding aliphatic polyester resin particles, the present inventors have found that, when the aliphatic polyester resin particles are expanded, if the amount of dispersant contained in the resulting expanded aliphatic polyester particles (adhered to the surface) is less than a certain amount, the aliphatic polyester expanded particles tend to adhere to each other (block). On the other hand, they have also found that, when molding the expanded aliphatic polyester particles, if the amount of dispersant contained in the expanded aliphatic polyester particles exceeds a certain amount, the resulting foamed article tends to have poor fusion properties.

[0006] One aspect of the present invention has been made in consideration of the above-mentioned problems, and its object is to provide a new method for producing aliphatic polyester-based expanded beads that can suppress adhesion between expanded beads during expansion and can provide aliphatic polyester-based expanded molded articles with excellent fusibility. [Means for solving the problem]

[0007] As a result of intensive research aimed at solving the above problems, the present inventors have discovered that expanding aliphatic polyester resin particles in the presence of a dispersant not only prevents mutual adhesion between the aliphatic polyester resin particles but also prevents mutual adhesion between the resulting expanded aliphatic polyester particles, and that washing the resulting expanded aliphatic polyester particles under specific conditions using a washing liquid containing a specific compound that can bond to the dispersant before molding enables the dispersant to be removed from the expanded aliphatic polyester particles, thereby improving the fusion properties of the foamed article, and have thus completed the present invention. That is, one aspect of the present invention comprises the following features. [1] A method for producing expanded aliphatic polyester particles, comprising: step (A) of expanding aliphatic polyester resin particles to obtain expanded aliphatic polyester particles; and step (B) of washing the expanded aliphatic polyester particles with a washing liquid, wherein step (A) comprises a dispersion step of dispersing the aliphatic polyester resin particles, an aqueous dispersion medium, a dispersant, and a blowing agent in a pressure-resistant vessel; and wherein in step (B), the washing liquid is an aqueous solution containing a water-soluble compound having, in its molecule, at least one functional group capable of bonding to the dispersant and at least one hydrophilic functional group, the temperature of the washing liquid being 30°C to 95°C, the concentration of the water-soluble compound in the washing liquid being 800 ppm to 70,000 ppm, and the amount of the washing liquid being 0.05 L to 0.50 L per 1 kg of the expanded aliphatic polyester particles. [2] The method for producing expanded aliphatic polyester beads according to [1], wherein the dispersant is at least one selected from the group consisting of tricalcium phosphate, calcium carbonate, and magnesium carbonate. [3] The method for producing aliphatic polyester-based expanded beads according to [1] or [2], wherein the water-soluble compound is any one of a water-soluble phosphate, a water-soluble condensed phosphate, or a mixture thereof. [4] The method for producing expanded aliphatic polyester beads according to any one of [1] to [3], wherein the water-soluble compound is sodium hexametaphosphate. [5] The method for producing expanded aliphatic polyester beads according to any one of [1] to [4], wherein step (B) includes a step of further washing the expanded aliphatic polyester beads after washing with the washing liquid with an aqueous solution having a concentration of the water-soluble compound of 0 ppm to 5 ppm. [6] The method for producing aliphatic polyester-based expanded beads according to [5], wherein the amount of the aqueous solution having a concentration of the water-soluble compound of 0 ppm to 5 ppm is 0.1 L to 1.0 L per 1 kg of the aliphatic polyester-based expanded beads. [7] The method for producing expanded aliphatic polyester beads according to any one of [1] to [6], wherein the expanded aliphatic polyester beads obtained in step (A) contain 2500 ppm to 5000 ppm of the dispersant. [8] The method for producing expanded aliphatic polyester beads according to any one of [1] to [7], wherein the expanded aliphatic polyester beads obtained in step (B) contain 1500 ppm or less of a dispersant. [9] A method for producing an aliphatic polyester-based expanded molded article, comprising a step of molding aliphatic polyester-based expanded beads obtained by the method for producing aliphatic polyester-based expanded beads according to any one of [1] to [8]. [Effects of the Invention]

[0008] According to one aspect of the present invention, a new method for producing aliphatic polyester-based expanded beads can be provided, which can suppress adhesion between expanded beads during expansion and can provide aliphatic polyester-based expanded molded articles with excellent fusion properties. DETAILED DESCRIPTION OF THE INVENTION

[0009] One embodiment of the present invention will be described below, but the present invention is not limited thereto. The present invention is not limited to the respective configurations described below, and various modifications are possible within the scope of the claims. Furthermore, embodiments or examples obtained by combining the technical means disclosed in different embodiments or examples are also included in the technical scope of the present invention. Furthermore, new technical features can be formed by combining the technical means disclosed in each embodiment. All academic literature and patent documents described in this specification are incorporated herein by reference. Furthermore, unless otherwise specified in this specification, the term "A to B" representing a numerical range means "greater than or equal to A (including and greater than A) and less than or equal to B (including and less than B)."

[0010] 1. Method for producing aliphatic polyester expanded beads A method for producing expanded aliphatic polyester beads according to one embodiment of the present invention includes step (A) of expanding aliphatic polyester resin particles to obtain expanded aliphatic polyester beads, and step (B) of washing the expanded aliphatic polyester beads with a washing liquid. Step (A) includes a dispersion step of dispersing the aliphatic polyester resin particles, an aqueous dispersion medium, a dispersant, and a blowing agent in a pressure-resistant vessel. In step (B), the washing liquid is an aqueous solution containing a water-soluble compound having at least one functional group capable of bonding to the dispersant and at least one hydrophilic functional group in the molecule. The temperature of the washing liquid is 30°C to 95°C, the concentration of the water-soluble compound in the washing liquid is 800 ppm to 70,000 ppm, and the amount of the washing liquid is 0.05 L to 0.50 L per 1 kg of the expanded aliphatic polyester beads. In this specification, "a method for producing aliphatic polyester resin particles according to one embodiment of the present invention" may be referred to as "the present production method," "aliphatic polyester resin particles" may be referred to as "resin particles," "aliphatic polyester resin particles according to one embodiment of the present invention" may be referred to as "the present resin particles," "aliphatic polyester expanded particles" may be referred to as "expanded particles," "aliphatic polyester expanded particles according to one embodiment of the present invention" may be referred to as "the present expanded particles," "aliphatic polyester expanded molded body" may be referred to as "expanded molded body," and "aliphatic polyester expanded molded body according to one embodiment of the present invention" may be referred to as "the present expanded molded body."

[0011] Since the present production method has the above-described configuration, it is possible to suppress mutual adhesion between the expanded beads obtained in step (A), and to provide a foamed molded article with excellent fusion properties from the expanded beads obtained through step (B).

[0012] (1-1. Aliphatic polyester resin particles) The present resin particles are resin particles containing an aliphatic polyester resin as a resin component. Specific examples of the aliphatic polyester resin contained in the present resin particles include polyhydroxyalkanoate (hereinafter sometimes referred to as "PHA") resins, polylactic acid, polybutylene succinate, polybutylene succinate adipate, polybutylene adipate terephthalate, polybutylene succinate terephthalate, and polycaprolactone. Among these aliphatic polyester resins, PHA resins are preferred because they are biodegradable in both soil and marine environments, and therefore more biodegradable. They can also be produced from plant materials, contributing to carbon neutrality. In other words, the present resin particles preferably contain a PHA resin as the aliphatic polyester resin.

[0013] The aliphatic polyester resin contained in the present resin particles preferably contains a PHA resin in an amount of 50% by weight or more, more preferably 60% by weight or more, more preferably 70% by weight or more, more preferably 80% by weight or more, even more preferably 90% by weight or more, even more preferably 95% by weight or more, and particularly preferably 100% by weight, based on 100% by weight of the aliphatic polyester resin. In other words, it is particularly preferable that the present resin particles contain only a PHA resin as a resin component.

[0014] PHA The PHA that the present resin particles may contain as a resin component will now be described in more detail. "PHA" is a general term for polymers containing hydroxyalkanoate as a monomer unit (monomer repeating unit) and is generally biodegradable. In particular, in this specification, "PHA" refers to a (co)polymer containing 50 mol% or more of hydroxyalkanoate repeating units out of all monomer repeating units (100 mol%), and a resin composed of such a (co)polymer. The PHA is preferably a (co)polymer containing 60 mol% or more, and more preferably 70 mol% or more, of all monomer repeating units (100 mol%). Note that in this specification, the term "(co)polymer" is intended to encompass both a homopolymer consisting of only one type of monomer and a copolymer consisting of two or more types of monomers.

[0015] Examples of PHA that the present resin particles may contain as a resin component include poly(3-hydroxyalkanoate) (hereinafter sometimes referred to as "P3HA") and poly(4-hydroxyalkanoate). Among these, P3HA is preferred because it can provide a molded product with excellent mechanical properties. In other words, the present resin particles are preferably P3HA-based resin particles.

[0016] P3HA is a 3-hydroxyalkanoate repeating unit of the formula: [—CHR—CH—CO—O—] (wherein R is C n H 2n+1 where n is an integer of 1 to 15.) as an essential repeating unit. In this specification, "P3HA" refers to a (co)polymer containing 50 mol % or more of the 3-hydroxyalkanoate repeating units out of all monomer repeating units (100 mol %).

[0017] Specific examples of P3HA include homopolymers of one or more monomers selected from the group consisting of 3-hydroxybutanoic acid (hereinafter sometimes referred to as "3HB"), 3-hydroxypropionic acid, 3-hydroxypentanoic acid, 3-hydroxyhexanoic acid, 3-hydroxyheptanoic acid, 3-hydroxyoctanoic acid, 3-hydroxynonanoic acid, 3-hydroxydecanoic acid, 3-hydroxyundecanoic acid, 3-hydroxydodecanoic acid, 3-hydroxytridecanoic acid, 3-hydroxytetradecanoic acid, 3-hydroxyhexadecanoic acid, and 3-hydroxyoctadecanoic acid, or copolymers of two or more of these monomers. Furthermore, P3HA may also be a copolymer of the above-mentioned P3HA-based repeating unit with a repeating unit other than P3HA. For example, P3HA may be a copolymer of the above-mentioned P3HA-based repeating unit and one or more monomers selected from the group consisting of 4-hydroxybutanoic acid, 4-hydroxypentanoic acid, 4-hydroxyhexanoic acid, 4-hydroxyheptanoic acid, 4-hydroxyoctanoic acid, 4-hydroxynonanoic acid, 4-hydroxydecanoic acid, 4-hydroxyundecanoic acid, 4-hydroxydodecanoic acid, 4-hydroxytridecanoic acid, 4-hydroxytetradecanoic acid, 4-hydroxyhexadecanoic acid, and 4-hydroxyoctadecanoic acid.

[0018] More specifically, examples of P3HA include 3HB homopolymers such as poly(3-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB"), poly(3-hydroxybutyrate-co-3-hydroxyhexanoate) (hereinafter sometimes referred to as "P3HB3HH"), poly(3-hydroxybutyrate-co-4-hydroxybutyrate) (hereinafter sometimes referred to as "P3HB4HB"), and poly(3-hydroxybutyrate-co-3-hydroxypropionate). Among these, P3HB, P3HB3HH, and P3HB4HB are preferred, with P3HB3HH and P3HB4HB being more preferred, due to the ease of industrial production using microorganisms.

[0019] In this specification, "poly(X-co-Y)" refers to a copolymer containing X repeating units and Y repeating units, and is intended to mean a copolymer obtained by copolymerizing a monomer from which the X repeating unit is derived and a monomer from which the Y repeating unit is derived. As described above, the name of a P3HA is determined by the repeating units contained in the P3HA. However, a very small amount (about 1 mol % or less) of a monomer contained in a P3HA may not be reflected in the name of the P3HA, provided that such a monomer does not significantly affect the physical properties of the P3HA. In other words, a P3HA may contain, in addition to the repeating units corresponding to its name, very small amounts of other repeating units.

[0020] When P3HA contains 3HB repeating units, from the viewpoint of the balance between flexibility and strength, the composition ratio of 3HB repeating units to repeating units other than 3HB repeating units (other repeating units) in the total monomer repeating units (100 mol%) in the P3HA (3HB repeating units / other repeating units) is preferably 99 / 1 (mol% / mol%) to 60 / 40 (mol% / mol%), more preferably 97 / 3 (mol% / mol%) to 70 / 30 (mol% / mol%), and even more preferably 95 / 5 (mol% / mol%) to 80 / 20 (mol% / mol%). When the composition ratio of 3HB repeating units in P3HA is 60 mol% or more, it is advantageous to provide a foamed molded article with superior rigidity. On the other hand, when the composition ratio of 3HB repeating units in P3HA is 99 mol% or less, it is advantageous to provide a foamed molded article with superior flexibility. The monomer composition ratio of P3HA can be measured by gas chromatography or the like (see, for example, WO 2014 / 020838).

[0021] P3HA can be produced by microorganisms. Examples of microorganisms capable of producing P3HA include Bacillus megaterium, a P3HB-producing bacterium discovered in 1925, as well as other naturally occurring microorganisms such as Cupriavidus necator (formerly Alcaligenes eutrophus and Ralstonia eutropha) and Alcaligenes latus. These microorganisms accumulate P3HB intracellularly.

[0022] Known microorganisms that produce P3HA, a copolymer of 3HB and other hydroxyalkanoic acids, include Aeromonas caviae, which produces P3HB3HH, and Alcaligenes eutrophus, which produces poly(3-hydroxybutyrate-co-4-hydroxybutyrate). To increase P3HB3HH productivity, Alcaligenes eutrophus AC32 (FERM BP-6038) (T. Fukui, Y. Doi, J. Bacteriol., 179, pp. 4821-4830 (1997)) is particularly preferred. In addition to the above, genetically modified microorganisms containing various P3HA synthesis-related genes can also be used depending on the desired physical properties of the foamed molded products.

[0023] Additives The resin particles may further contain additives (other additives) in addition to the aliphatic polyester resin. Examples of other additives include crosslinkers, crystal nucleating agents, cell regulators, lubricants, plasticizers, antistatic agents, flame retardants, conductive agents, heat insulating agents, antioxidants, UV absorbers, colorants, inorganic fillers, organic fillers, hydrolysis inhibitors, nonionic water-soluble polymers, etc. Depending on various purposes, one type of other additive may be used alone, or two or more types may be used in combination. As the other additives, biodegradable additives are particularly preferred.

[0024] Examples of nucleating agents include pentaerythritol, orotic acid, aspartame, cyanuric acid, glycine, zinc phenylphosphonate, and boron nitride. One of these nucleating agents may be used alone, or two or more may be used in combination. When two or more nucleating agents are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0025] Examples of the cell regulator include talc, silica, calcium silicate, calcium carbonate, aluminum oxide, titanium oxide, diatomaceous earth, clay, sodium bicarbonate, alumina, barium sulfate, aluminum oxide, and bentonite. Among these cell regulators, talc is preferred because of its particularly excellent dispersibility in aliphatic polyesters. One of these cell regulators may be used alone, or two or more may be used in combination. When two or more cell regulators are used in combination, the mixing ratio may be appropriately adjusted depending on the purpose.

[0026] Examples of lubricants include behenamide, oleamide, erucamide, stearamide, palmitamide, N-stearylbehenamide, N-stearylerucamide, ethylenebisstearamide, ethylenebisoleamide, ethylenebiserucamide, ethylenebislauricamide, ethylenebiscapricamide, p-phenylenebisstearamide, and polycondensates of ethylenediamine, stearic acid, and sebacic acid.

[0027] Examples of the antistatic agent include coconut oil fatty acid diethanolamide, etc. The content of the antistatic agent in the resin particles is not particularly limited.

[0028] It is preferable that the resin particles further contain a nonionic water-soluble polymer because this can reduce the apparent density and / or improve compatibility with the aliphatic polyester resin. In other words, it is preferable that the resin particles contain a nonionic water-soluble polymer. A nonionic water-soluble polymer is a polymer that does not ionize when dissolved in water.

[0029] Manufacturing method of resin particles The method for producing the resin particles is not particularly limited, and the resin particles can be produced, for example, by a method including a melt-kneading step of melt-kneading a resin composition containing an aliphatic polyester resin and other optional additives, and a particle forming step of forming the melt-kneaded resin composition into a shape that is easy to use for foaming. The production method may include a resin particle preparation step including the above steps prior to step (A).

[0030] (Process (A)) The present production method includes a step (A) of expanding the present resin particles to obtain the present expanded particles. Specific embodiments of step (A) are not particularly limited as long as they include a dispersion step of dispersing the present resin particles, an aqueous dispersion medium, a dispersant, and a blowing agent in a pressure-resistant vessel and can obtain the present expanded particles.

[0031] ·Dispersion process The dispersion step is a substep of dispersing the resin particles, an aqueous dispersion medium, a dispersant, and a blowing agent in a pressure-resistant vessel. The dispersion step can also be said to be a step of dispersing the resin particles, a dispersant, and a blowing agent in the aqueous dispersion medium in the pressure-resistant vessel.

[0032] In the dispersion step, in addition to the above-mentioned substances, a crosslinking agent, a crosslinking aid, a dispersing aid, and / or a plasticizer may be further dispersed in the aqueous dispersion medium as needed. Therefore, the dispersion step can also be said to be a step of preparing a dispersion in a container in which the resin particles, a dispersing agent, a foaming agent, and as needed, a crosslinking agent, a crosslinking aid, a dispersing aid, and / or a plasticizer are dispersed.

[0033] The vessel used in the dispersion step is not particularly limited, but is preferably one that can withstand the foaming temperature and foaming pressure described below, for example, a pressure-resistant vessel.

[0034] The aqueous dispersion medium used in the dispersion step is not particularly limited as long as it can uniformly disperse at least the resin particles, dispersant, and blowing agent. Since this allows for stable production of expanded particles, it is preferable to use pure water or ultrapure water, such as RO water (water purified by reverse osmosis), distilled water, or deionized water (water purified by ion exchange resin). Alternatively, tap water and / or industrial water can be used as the aqueous dispersion medium.

[0035] Examples of dispersants used in the dispersion step include inorganic substances such as tricalcium phosphate, trimagnesium phosphate, magnesium carbonate, calcium carbonate, barium sulfate, kaolin, talc, clay, aluminum oxide, titanium oxide, and aluminum hydroxide. As the dispersant, one of these compounds may be used alone, or two or more may be used in combination. Among these compounds, it is preferable that the dispersant be at least one selected from the group consisting of tricalcium phosphate, calcium carbonate, and magnesium carbonate, as this is easy to wash off from the surface of the expanded beads.

[0036] The amount of dispersant used in the dispersion step is not particularly limited. However, from the viewpoint of providing expanded beads with sufficient dispersant adhered to the surface and suppressing mutual adhesion between the expanded beads, the amount is preferably 0.5 to 5.0 parts by weight, more preferably 0.8 to 4.0 parts by weight, and even more preferably 1.0 to 3.0 parts by weight, per 100 parts by weight of resin particles used in the dispersion step. In particular, by using an amount of dispersant of 1.5 parts by weight or more per 100 parts by weight of resin particles, expanded beads with a larger amount of dispersant adhered to the surface (specifically, more than 3000 ppm) can be provided, thereby further suppressing mutual adhesion between the expanded beads. Furthermore, by using an amount of dispersant of 5.0 parts by weight or less, the use of excess dispersant can be suppressed, which is economically advantageous and improves the efficiency of washing the expanded beads in step (B).

[0037] Examples of foaming agents used in the dispersion step include inorganic gases such as nitrogen, carbon dioxide, and air; saturated hydrocarbons having 3 to 5 carbon atoms such as propane, normal butane, isobutane, normal pentane, isopentane, and neopentane; ethers such as dimethyl ether, diethyl ether, and methyl ethyl ether; halogenated hydrocarbons such as monochloromethane, dichloromethane, and dichlorodifluoroethane; and water. Among these, nitrogen or carbon dioxide is preferably used as the foaming agent because of its low environmental impact and excellent foaming power. These compounds may be used alone or in combination as a mixture of two or more.

[0038] In the dispersion step, a dispersing aid may be used to prevent the resin particles from adhering to each other. Examples of the dispersing aid include anionic surfactants such as sodium alkanesulfonate, sodium alkylbenzenesulfonate, and sodium α-olefinsulfonate. As the dispersing aid, one of these compounds may be used alone, or two or more may be used in combination.

[0039] In the dispersion step, a crosslinking agent may be used to crosslink molecular chains of the aliphatic polyester resin in the resin particles and provide expanded beads with a wide molding temperature range. The crosslinking agent is not particularly limited as long as it can crosslink molecular chains of the aliphatic polyester resin, but an organic peroxide is preferably used.

[0040] As the organic peroxide used as the crosslinking agent, an organic peroxide having a one-hour half-life temperature of 90°C to 160°C is preferred, and an organic peroxide having a one-hour half-life temperature of 115°C to 125°C is more preferred, because it can introduce sufficient crosslinking and suppress the remaining unreacted crosslinking agent. Specific examples of such organic peroxides include 1,1-di(t-butylperoxy)cyclohexane (one-hour half-life temperature 111°C), 2,2-di(t-butylperoxy)butane (one-hour half-life temperature 122°C), n-butyl 4,4-di(t-butylperoxy)valerate (one-hour half-life temperature 126°C), 2,2-di(4,4-di(t-butylperoxy)cyclohexyl)propane (one-hour half-life temperature 114°C), 1,1-di(t-hexylperoxy)cyclohexane ( 1-hour half-life temperature: 107°C), benzoyl peroxide (1-hour half-life temperature: 92°C), t-butylperoxy-2-ethylhexyl carbonate (1-hour half-life temperature: 121°C), t-butylperoxyisopropyl carbonate (1-hour half-life temperature: 118°C), t-amylperoxy-2-ethylhexyl carbonate (1-hour half-life temperature: 117°C), t-amylperoxyisopropyl carbonate (1-hour half-life temperature: 115°C), t-butylperoxyisobutyrate (1-hour half-life temperature: 93°C), t-butyl peroxy-2-ethylhexanoate (1-hour half-life temperature: 95°C), t-butyl peroxyisononanoate (1-hour half-life temperature: 123°C), t-butyl peroxyacetate (1-hour half-life temperature: 123°C), t-butyl peroxydibenzoate (1-hour half-life temperature: 125°C), t-amyl peroxyisobutyrate (1-hour half-life temperature: 93°C), t-amyl peroxy-2-ethylhexanoate (1-hour half-life temperature: 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 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), and the like.

[0041] In the dispersion step, a crosslinking aid may be used to improve the crosslinking efficiency of the aliphatic polyester resin. Examples of the crosslinking aid include compounds having at least one unsaturated bond in the molecule, more specifically, allyl esters, acrylic esters, methacrylic esters, divinyl compounds, etc. Note that, as the crosslinking aid, one of these compounds may be used alone, or two or more may be used in combination.

[0042] In the dispersion step, a plasticizer may be used to improve the expansion ratio of the expanded particles. Examples of plasticizers include glycerin ester compounds such as glycerin diacetomonolaurate, citrate ester compounds such as acetyl tributyl citrate, sebacate ester compounds such as dibutyl sebacate, adipate ester compounds, polyether ester compounds, benzoate ester compounds, phthalate ester compounds, isosorbide ester compounds, polycaprolactone compounds, and dibasic acid ester compounds such as benzyl methyl diethylene glycol adipate. As the plasticizer, one of these compounds may be used alone, or two or more may be used in combination.

[0043] Heating process, pressure rising process and holding process Step (A) preferably includes a heating step of raising the temperature inside a container containing the dispersion obtained in the dispersing step, in which the resin particles, dispersant, and foaming agent are dispersed in an aqueous dispersion medium, to a constant temperature (foaming temperature), a pressure raising step of raising the pressure inside the container to a constant pressure (foaming pressure), and / or a maintaining step of maintaining the temperature and pressure inside the container at a constant temperature and / or constant pressure (i.e., the foaming temperature and / or foaming pressure).

[0044] The foaming temperature in the temperature-raising step is not particularly limited, but is preferably 120.0°C to 140.0°C, more preferably 125.0°C to 135.0°C, and even more preferably 130.0°C to 133.0°C, because this allows the crosslinking reaction by the organic peroxide to proceed quickly and also allows hydrolysis of the aliphatic polyester resin to be suppressed during the foaming process. Furthermore, the rate at which the temperature is raised to the desired foaming temperature in the temperature-raising step is not particularly limited, but may be, for example, 1.0°C / min to 3.0°C / min.

[0045] The expansion pressure in the pressure increasing step is not particularly limited, but is preferably 1.0 MPa to 10.0 MPa (gauge pressure), more preferably 2.0 MPa to 5.0 MPa (gauge pressure), and even more preferably 2.5 MPa to 4.0 MPa, since expanded beads with a higher expansion ratio can be provided.

[0046] In the holding step, the time for which the temperature and pressure in the container are held at the foaming temperature and / or foaming pressure is not particularly limited, but is preferably 20 minutes or more, more preferably 30 minutes or more, from the viewpoint of fully exerting the desired effects of the temperature and pressure increase. In the holding step, (1) when only the temperature increase step is performed, it is preferable to hold at least the temperature in the container constant, (2) when only the pressure increase step is performed, it is preferable to hold at least the pressure in the container constant, and (3) when both the temperature increase step and the pressure increase step are performed, it is preferable to hold both the temperature and pressure in the container constant.

[0047] In one embodiment of the present invention, since the crosslinking reaction by the organic peroxide can proceed more quickly and hydrolysis of the aliphatic polyester resin during the foaming process can be suppressed, step (A) more preferably includes a temperature increasing step of increasing the temperature in the container to 120°C to 140°C, a pressure increasing step of increasing the pressure in the container to 1.0 MPa to 10.0 MPa (gauge pressure), and a holding step of holding the temperature and pressure in the container for 20 minutes or more.

[0048] (Release process) The present production method includes a dispersing step in which one end of a container containing a dispersion obtained by dispersing the present resin particles, a dispersant, and a blowing agent in an aqueous dispersion medium in the dispersing step, preferably a dispersion that has been subjected to a temperature increase, pressure increase, and / or holding step, is opened and the dispersion in the container is released into a region with a pressure lower than the pressure in the container. By carrying out the releasing step, the resin particles can be expanded, resulting in expanded particles.

[0049] In the releasing step, the "region under a pressure lower than the pressure inside the container" refers to "a region under a pressure lower than the pressure inside the container" or "a space under a pressure lower than the pressure inside the container", and can also be referred to as "an atmosphere under a pressure lower than the pressure inside the container". The region under a pressure lower than the pressure inside the container is not particularly limited as long as it is lower than the foaming pressure, and may be, for example, a region under atmospheric pressure. Furthermore, when a temperature-pressure increasing step is performed, the "pressure inside the container" in the releasing step can also be referred to as the "foaming pressure".

[0050] In the release step, the pressure in the region lower than the pressure inside the container is not particularly limited as long as it is a region lower than the pressure inside the container, and in particular, when a pressure increase step is carried out in the dispersion step, the pressure in the region lower than the pressure inside the container may be atmospheric pressure.

[0051] In the discharging step, when discharging the dispersion into a region with a lower pressure than the pressure inside the container, it is preferable to discharge the dispersion through an orifice having a diameter of 1 mm to 5 mm provided in the container, since this allows the flow rate of the dispersion to be adjusted and allows homogeneous expanded beads to be obtained.

[0052] The content of dispersant in the expanded particles obtained by step (A) Aliphatic polyester resins have a slower crystallization rate than thermoplastic resins such as polyolefins that have traditionally been used in expanded beads. Therefore, expanded beads containing aliphatic polyester resins have the problem of easily adhering to each other during expansion. However, the present inventors have found that the higher the dispersant content of the expanded beads, the more effectively the expanded beads are prevented from adhering to each other during expansion. In particular, when the dispersant content of the expanded beads is 2500 ppm or more, a particularly excellent effect of preventing adhering to each other can be obtained.

[0053] From the above viewpoints, the content of dispersant in the expanded beads obtained by step (A) (in other words, the amount of dispersant adhering to the surface of the expanded beads obtained by step (A), which is the content of dispersant in the expanded beads before they are washed in the subsequent step (B)) is preferably 1500 ppm to 7500 ppm, more preferably 2000 ppm to 5000 ppm, and from the viewpoint of obtaining a particularly excellent effect of inhibiting mutual adhesion, even more preferably 2500 ppm to 5000 ppm, even more preferably 3000 ppm to 5000 ppm. The content of dispersant in the expanded beads obtained by step (A) can be adjusted by, for example, the amount of dispersant or dispersion aid used in the dispersion step of step (A).

[0054] In this specification, the content of the dispersant in the expanded beads is a value expressed in parts per million based on the weight of the expanded beads, and is a value measured by the method described in the examples.

[0055] (Process (B)) This production method includes step (B) of washing the expanded beads obtained in step (A) with a washing liquid. Step (B) can also be said to be a step of removing the dispersant contained in the expanded beads obtained in step (A) (adhering to the surface of the expanded beads).

[0056] Expanded beads that have a large amount of dispersant attached to their surfaces to prevent them from sticking to each other during expansion have the problem that the expanded beads are less likely to fuse together when molded, resulting in poor fusion properties for the resulting molded foam. In this production method, however, by carrying out step (B), the dispersant attached to the surfaces of the expanded beads obtained in step (A) can be removed. Because the amount of dispersant on the surfaces of the expanded beads that have undergone step (B) has been sufficiently reduced, the expanded beads are more likely to fuse together when molded, making it possible to provide a molded foam with excellent fusion properties.

[0057] Cleaning solution In step (B), the washing liquid used to wash the expanded beads obtained in step (A) is an aqueous solution containing a water-soluble compound (hereinafter sometimes simply referred to as a "water-soluble compound") having, in its molecule, at least one functional group capable of bonding to the dispersant used in step (A) and at least one hydrophilic functional group. In this specification, "capable of bonding to the surface of a dispersant" means that the compound has an ionicity opposite to that of the surface of the target dispersant and is capable of forming an ionic bond. Therefore, "functional group capable of bonding to a dispersant" refers to a functional group having an ionicity opposite to that of the surface of the target dispersant. Furthermore, "hydrophilic functional group" refers to a polar group or dissociative group that can form a weak bond with water molecules through electrostatic interaction or hydrogen bonding, and exhibits affinity for water.

[0058] More specifically, for example, when a dispersant with a positively charged surface (e.g., tricalcium phosphate) is used in step (A), functional groups that can bond to such dispersants include anionic functional groups such as phosphate groups (ions), carboxyl groups (ions), and silicate ions, and hydrophilic functional groups include phosphate groups (ions), carboxyl groups (ions), silicate ions, and alcoholic hydroxyl groups. Furthermore, when a dispersant with a negatively charged surface (e.g., kaolin) is used in step (A), functional groups that can bond to such dispersants include cationic functional groups such as amino groups (ions), quaternary ammonium ions, and pyridinium groups, and hydrophilic functional groups include amino groups (ions), quaternary ammonium ions, pyridinium groups, and alcoholic hydroxyl groups.

[0059] The number of "functional groups capable of bonding to a dispersant" and "hydrophilic functional groups" possessed by the water-soluble compound is not particularly limited as long as they are one or more of each, but from the viewpoint of further improving the detergency of the cleaning liquid, it is preferable for at least one of the "functional groups capable of bonding to a dispersant" and the "hydrophilic functional groups" to be two or more, and it is more preferable for the water-soluble compound to have two or more of each of the "functional groups capable of bonding to a dispersant" and the "hydrophilic functional groups." Furthermore, the upper limit of the number of "functional groups capable of bonding to a dispersant" and the "hydrophilic functional groups" possessed by the water-soluble compound is not particularly limited, but may be, for example, 500 or less.

[0060] Among the functional groups, there are functional groups that are capable of bonding to the surface of a dispersant and are hydrophilic; such functional groups may be regarded as either "functional groups capable of bonding to a dispersant" or "hydrophilic functional groups," and a water-soluble compound having one such functional group can be regarded as a water-soluble compound having at least one functional group capable of bonding to a dispersant and at least one hydrophilic functional group within the molecule.

[0061] Examples of water-soluble compounds that can be used when a dispersant with a positively charged surface is used in step (A) include water-soluble phosphates such as sodium triphosphate and potassium triphosphate; water-soluble condensed phosphates such as sodium pyrophosphate, sodium tripolyphosphate, and sodium hexametaphosphate; water-soluble phosphates such as sodium triphosphate and potassium triphosphate; water-soluble silicates such as sodium metasilicate and sodium orthosilicate; water-soluble ethylenediamine tetraacetates such as disodium ethylenediamine tetraacetate and tetrasodium ethylenediamine tetraacetate; water-soluble citrates such as sodium citrate; water-soluble tartrates such as sodium tartrate; mixtures of the water-soluble citrates and water-soluble tartrates (water-soluble hydroxycarboxylates); and sodium polyacrylate. These water-soluble compounds may be used alone or in combination. Among these, water-soluble phosphates, water-soluble condensed phosphates, or mixtures thereof are preferred because they are easily removed by washing from the surface of the expanded beads. Sodium hexametaphosphate is particularly preferred because it produces a washing solution with a weakly acidic pH, making the washing solution easy to handle.

[0062] Examples of water-soluble compounds that can be used when a dispersant with a negatively charged surface is used in step (A) include water-soluble polyvinylpyridinium compounds such as poly-4-vinyl-N-ethylpyridinium bromide; polyoxyethylene alkylamines; ethylenediamine tetraacetates such as disodium ethylenediamine tetraacetate and tetrasodium ethylenediamine tetraacetate; ethylenediamine hydrochloride, etc. These water-soluble compounds may be used alone or in combination of two or more.

[0063] The concentration of the water-soluble compound in the cleaning solution used in step (B) is 800 ppm to 70,000 ppm. By setting the concentration of the water-soluble compound in the cleaning solution to 800 ppm or more, a sufficient cleaning effect can be achieved, and by setting it to 70,000 ppm or less, an effect corresponding to the concentration of the water-soluble compound can be obtained, which has the advantage of preventing economic waste. Since the expanded beads can be washed with a smaller amount of cleaning solution and the burden on treating wastewater after washing can be reduced, the higher the concentration of the water-soluble compound in the cleaning solution within the above range, the more preferable it is; specifically, it is preferably 5,000 ppm or more, and more preferably 10,000 ppm or more.

[0064] The temperature of the cleaning liquid used in step (B) is 30°C to 95°C. By setting the temperature of the cleaning liquid to 30°C to 95°C, the cleaning effect of the cleaning liquid can be further improved. From the viewpoint of further improving the cleaning effect of the cleaning liquid, the temperature of the cleaning liquid used in step (B) is preferably 35°C to 85°C, and more preferably 40°C to 75°C.

[0065] The amount of the cleaning liquid used in step (B) is 0.05 L to 0.50 L per 1 kg of the aliphatic polyester-based expanded beads subjected to step (B). Using a cleaning liquid amount of 0.05 L to 0.50 L is economically advantageous and also reduces the burden on wastewater treatment after washing. From the above perspectives, the smaller the amount of cleaning liquid used in step (B), the more preferable. Specifically, the amount is preferably 0.05 L to 0.30 L, more preferably 0.05 L to 0.20 L, per 1 kg of the aliphatic polyester-based expanded beads subjected to step (B). When reducing the amount of cleaning liquid, it is preferable to increase the concentration of the water-soluble compound in the cleaning liquid in order to remove as much dispersant as possible. From the perspective of removing as much dispersant as possible with a smaller amount of cleaning liquid, it is particularly preferable to use a cleaning liquid having a water-soluble compound concentration of 5,000 ppm to 70,000 ppm in step (B) in an amount of 0.05 L to 0.30 L per 1 kg of the expanded beads.

[0066] Second wash Step (B) preferably includes a step (hereinafter sometimes referred to as the "second washing step") of further washing the expanded beads, which have been washed with a washing solution containing the water-soluble compound at a concentration of 5,000 ppm to 70,000 ppm (hereinafter sometimes referred to as the "first washing step"), with an aqueous solution containing 0 ppm to 5 ppm of the water-soluble compound (hereinafter sometimes referred to as the "second washing solution"). By carrying out the second washing step, it is possible to further remove the dispersant from the surface of the expanded beads and also remove the washing solution that has adhered in the first washing step, thereby providing expanded beads that can provide expanded molded articles with better internal fusion.

[0067] The second cleaning solution used in the second cleaning step is an aqueous solution containing 0 ppm to 5 ppm of a water-soluble compound. The water-soluble compound that the second cleaning solution may contain is the same as the "water-soluble compound having, in the molecule, at least one functional group capable of bonding to the dispersant used in step (A) and at least one hydrophilic functional group," as described above. Therefore, the specific aspects of the water-soluble compound will be omitted in this section, and the above description will be used as appropriate.

[0068] In this specification, the term "aqueous solution containing 0 ppm to 5 ppm of a water-soluble compound" refers to an aqueous solution containing 0 ppm of a water-soluble compound, in other words, water containing no water-soluble compound (pure water), and an aqueous solution containing more than 0 ppm but not more than 5 ppm of a water-soluble compound. As the second cleaning solution used in the second cleaning step, either pure water or an aqueous solution containing more than 0 ppm but not more than 5 ppm of a water-soluble compound can be used, but pure water is preferred because it has a better cleaning effect.

[0069] The temperature of the second cleaning solution used in the second cleaning step is not particularly limited, but is preferably 35 to 85° C., and more preferably 40 to 75° C. By setting the temperature of the second cleaning solution to 30 to 95° C., the cleaning effect of the cleaning solution can be further improved.

[0070] The amount of the second washing liquid used in the second washing step is preferably 0.1 L to 1.0 L, more preferably 0.5 L to 0.9 L, per 1 kg of the expanded aliphatic polyester beads subjected to step (B). Setting the amount of the second washing liquid to 0.1 L to 1.0 L has the advantage of reducing the amount of water adhering to the expanded beads.

[0071] ·Drying process Step (B) may include a drying step of drying the washed expanded beads. The drying method in the drying step is not particularly limited, and methods using a channel-type or cylindrical agitator dryer, a box-type or band-type through-air dryer, a fluidized bed dryer, or the like can be used. The drying temperature is also not particularly limited, and drying can be carried out at a temperature of, for example, 60°C to 100°C, preferably 80°C to 90°C.

[0072] The content of dispersant in the expanded particles after step (B) From the viewpoint of providing a foamed molded article with excellent internal fusion properties, the lower the dispersant content of the expanded beads obtained in step (B) (in other words, the amount of dispersant adhering to the surface of the expanded beads obtained in step (B), i.e., the content of dispersant in the expanded beads after washing in step (B)), the better. Specifically, it is preferably 1500 ppm or less, more preferably 100 ppm or less, even more preferably 800 ppm or less, and particularly preferably 300 ppm or less. By setting the dispersant content of the expanded beads obtained in step (B) to 1500 ppm or less, it is possible to provide a foamed molded article with excellent internal fusion properties, and by setting it to 300 ppm or less, it is possible to provide a foamed molded article with particularly excellent internal fusion properties. The dispersant content of the expanded beads obtained in step (B) can be adjusted by the amount of dispersant used in step (A) as well as the concentration, temperature, and amount of the washing solution used in step (B).

[0073] Apparent density of foam particles The apparent density of the expanded beads obtained by this production method is not particularly limited, but is preferably 20 g / L to 80 g / L, and more preferably 30 g / L to 70 g / L. If the apparent density of the expanded beads is within the above range, it is possible to provide an expanded molded article that is lightweight and has good strength (compressive strength). In this specification, the apparent density of the expanded beads is a value measured by the method described in the examples.

[0074] 2. Method for producing aliphatic polyester foam molded products In one embodiment of the present invention, there is provided a method for producing an aliphatic polyester foam molded article, which includes a step of molding the expanded beads obtained by the present production method (i.e., the present expanded beads). In the following description, the "method for producing an aliphatic polyester foam molded article according to one embodiment of the present invention" may be referred to as the "method for producing the present foam molded article."

[0075] The foamed molded article obtained by the present foamed molded article manufacturing method is a foamed molded article made from the present foamed beads as a raw material. Therefore, the foamed molded article has excellent internal fusion properties. The internal fusion properties of the foamed molded article can be evaluated by the method described in the examples.

[0076] In the method for producing the present foamed molded article, the method for molding the present foamed beads is not particularly limited, and known molding methods can be applied. Examples of the method for molding the present foamed beads in the method for producing the present foamed molded article include the following molding methods (A) to (D): (A) A method in which the expanded beads are pressurized with an inorganic gas in a container to impregnate the expanded beads with the inorganic gas, and then a predetermined internal pressure is applied to the expanded beads, and the expanded beads are then filled into a mold and heated with steam; (B) A method in which the expanded beads are filled into a mold, compressed so as to reduce the volume of the mold by 10% to 75%, and then heated with steam; (C) A method in which the expanded beads are compressed by gas pressure, filled into a mold, and heated with steam, utilizing the recovery force of the expanded beads; (D) A method in which the foamed particles are filled into a mold without any particular pretreatment and heated with steam.

[0077] Applications of foam moldings The foam molded articles produced by this method for producing foam molded articles can be suitably used in a variety of fields, including packaging cushioning materials (e.g., cushioning materials for packaging home appliances such as refrigerators, freezers, air conditioner bodies and their outdoor units, washing machines, air purifiers, humidifiers, rice cookers, microwave ovens, ovens, toasters, electric fans, and storage battery units; and cushioning materials for packaging automotive items such as transmissions, roofs, hoods, doors, batteries, and engines), automotive components (e.g., bumper cores, headrests, luggage boxes, tool boxes, floor spacers, seat cores, child car seat cores, sun visor cores, and knee pads), heat insulating materials (e.g., containers for constant temperature storage and containers for constant temperature transportation), casting models, agricultural product boxes, fish boxes, building materials, and civil engineering materials. [Example]

[0078] The present invention will be specifically explained below with reference to examples, but the technical scope of the present invention is not limited to these examples.

[0079] 〔material〕 The substances used in the examples and comparative examples are shown below.

[0080] (Aliphatic polyester resin) Aliphatic polyester resin: poly-3-hydroxybutyrate-co-3-hydroxyhexanoate copolymer (Kaneka Biodegradable Biopolymer Green Planet X131N, manufactured by Kaneka Corporation).

[0081] (Foam adjuster) Foam adjuster: Talc (Micro Ace K-1 manufactured by Nippon Talc Co., Ltd.).

[0082] (dispersant) Dispersant: tribasic calcium phosphate (manufactured by Taihei Chemical Industry Co., Ltd.).

[0083] (Dispersion aid) Dispersing aid: sodium alkylsulfonate (Latemul (registered trademark) PS manufactured by Kao Corporation).

[0084] (Crosslinking agent) Crosslinking agent: 1,1-di(t-butylperoxy)cyclohexane (Perhexa (registered trademark) C-80(S), manufactured by NOF Corporation, purity 80%).

[0085] (water soluble compound) Sodium hexametaphosphate (manufactured by WUXI LOTUS ESSENCE) (antistatic agent) Antistatic agent: coconut oil fatty acid diethanolamide (Profan 128 Extra manufactured by Sanyo Chemical Industries, Ltd.).

[0086] [Measurement method] The methods for measuring and evaluating the various physical properties carried out in the examples and comparative examples are as follows.

[0087] (Measurement of weight per resin particle) One hundred resin particles were randomly selected and their total weight Wp (mg) was measured, and the weight per resin particle was calculated as Wp / 100 (mg).

[0088] (Measurement of apparent density of expanded particles) The method for measuring the apparent density of the expanded beads was as follows (1) to (3): (1) A measuring cylinder containing ethanol was prepared, and expanded beads with a weight Wd (g) were submerged in the ethanol; (2) The volume of the expanded beads, read from the rise in the water level of the ethanol (submersion method), was calculated as Vd (cm 3 (3) The apparent density ρd of the expanded beads was calculated using the following formula: Apparent density of foam particles ρd (g / cm 3 )=Wd / Vd.

[0089] (Dispersant content of expanded particles (amount of attached dispersant)) The method for measuring the dispersant content of the expanded particles was as follows (1) to (4): (1) An aqueous solution (colorimetric solution) containing 0.022 wt% ammonium metavanadate, 0.54 wt% ammonium molybdate, and 3 wt% nitric acid was prepared; (2) 50.0 mL of this colorimetric solution and W (g) of expanded particles were added to a conical beaker and mixed; (3) The mixture was stirred for 1 minute and then left to stand for 10 minutes; (4) The liquid phase after standing was collected in a quartz cell with a light path length of 1.0 cm, and the absorbance A at 410 nm was measured using a UV-visible spectrophotometer (Shimadzu UV-1280).

[0090] The dispersant content of the foamed particles was calculated using the absorbance coefficient ε (g / L cm) of the dispersant at 410 nm, which was calculated by mixing a known amount of dispersant in the same colorimetric solution, according to the following formula: Dispersant content of foam particles (ppm) = 5.0 x 10 4 ·ε·A / W.

[0091] (Evaluation of adhesion of foam particles to each other) 100 g of expanded beads were weighed out, and from these 100 g of expanded beads, those that had adhered to each other (two or more expanded beads stuck together) were selected and their total weight was measured. The adhesion of the expanded beads to each other was evaluated according to the following criteria. A (good): The total amount of foamed particles that have adhered to each other is less than 1 g per 100 g of foamed particles. B (pass): The total amount of foamed particles stuck together in 100 g of foamed particles is 1 g or more and less than 10 g. C (poor): The total amount of foamed particles that are stuck together is 10 g or more per 100 g of foamed particles.

[0092] (Measurement of internal pressure of foamed beads) The internal pressure of the expanded beads was measured by the following methods (1) to (5): (1) the weight W1 (g) of the expanded beads was measured; (2) the expanded beads were heated at 150°C for 30 minutes to allow the inorganic gas inside the expanded beads to dissipate; (3) the weight W2 (g) of the expanded beads from which the inorganic gas had dissipated was measured again; (4) the weight of the inorganic gas (ΔW) was calculated from the difference in weight (W1 - W2) of the expanded beads before and after the inorganic gas had dissipated; (5) the internal pressure P (MPa) of the expanded beads was calculated using the equation of state of an ideal gas (specifically, the following formula): Internal pressure P (MPa) = (1 + ΔW / M × 0.082 × (273 + T) × (ρd × 1000 / W2)) / 9.87. In the above formula, M is the average molar molecular weight, T is the temperature (room temperature) (°C) when the weight of the expanded beads is measured, and ρd is the apparent density (g / cm) of the expanded beads (expanded beads with a weight W1) after the pressurizing step. 3 )

[0093] (Evaluation of fusion properties of foam molded products) A crack approximately 5 mm deep was made with a cutter knife in the center of the largest surface of the foamed molded article, and the foamed molded article was split along the crack and the fractured surface was observed. The ratio of the number of broken foamed beads (broken beads) to the total number of foamed beads present on the fractured surface was calculated, and the fusion property of the foamed molded article was evaluated according to the following criteria. A (particularly good): The ratio of the number of broken particles to the total number of foamed particles is 90% or more. B (Good): The ratio of the number of broken particles to the total number of expanded particles is 60% to 90%. C (Poor): The ratio of the number of broken particles to the total number of expanded particles is 30% to 60%. D (particularly poor): The ratio of the number of broken particles to the total number of expanded particles is 30% or less.

[0094] Example 1 (Production of resin particles) 100.0 parts by weight of an aliphatic polyester resin and 0.10 parts by weight of a cell control agent were weighed and dry-blended. The dry-blended mixture was melt-kneaded using a twin-screw extruder (TEM-26SX, manufactured by Toshiba Machine Co., Ltd.) at a cylinder temperature of 130°C to 160°C and extruded from a die nozzle attached to the tip of the extruder. The molten aliphatic polyester resin composition extruded from the nozzle at 182°C was water-cooled to 43°C. A small amount of antistatic agent diluted with water was applied to the surface of the water-cooled aliphatic polyester resin composition strand, and the strand was then cut to obtain resin particles. The resulting resin particles weighed 1.6 mg per particle.

[0095] (Process (A)) 100 parts by weight of the resulting resin particles, 200 parts by weight of pure water, 1.5 parts by weight of dispersant, 0.13 parts by weight of dispersing aid, and 2.7 parts by weight of crosslinker were placed in a pressure vessel under stirring, and then thoroughly aerated with carbon dioxide to remove oxygen from the pressure vessel. Next, carbon dioxide was introduced into the pressure vessel as a blowing agent. This procedure yielded a dispersion of resin particles, dispersant, blowing agent, dispersing aid, and crosslinker in pure water (an aqueous dispersion medium). The dispersion in the pressure vessel was then heated to a foaming temperature of 128.5°C. Additional carbon dioxide was then introduced to raise the pressure to a foaming pressure of 3.3 MPa (gauge pressure), and the pressure vessel was maintained at this foaming temperature and pressure for 40 minutes. The valve at the bottom of the pressure vessel was then opened, and the contents of the pressure vessel were released to atmospheric pressure through a 3.6 mm diameter orifice, yielding expanded beads. The resulting expanded beads were evaluated for adhesion to each other, and the dispersant content (before washing) was measured. The results are shown in Table 1.

[0096] (Process (B)) The expanded beads obtained in step (A) immediately after release were washed with a washing solution prepared by dissolving sodium hexametaphosphate, a water-soluble compound having at least one functional group capable of bonding to the dispersant (tricalcium phosphate) and one hydrophilic functional group in the molecule, in pure water to a concentration of 10,000 ppm. The temperature of the washing solution was 70°C, and the amount of washing solution was 0.1 L per 1 kg of expanded beads.

[0097] Immediately after washing with the above-mentioned washing liquid, the expanded beads were further washed with 0.8 L of pure water per 1 kg of the expanded beads (second washing).

[0098] The expanded beads were measured for apparent density and the amount of dispersant adhered thereto (after washing). The results are shown in Table 1.

[0099] (Production of foam molded products) The expanded beads obtained in step (B) were placed in a pressure-resistant container heated to 80°C and pressurized with air until the internal pressure of the expanded beads reached 0.18 MPa (absolute pressure). The pressurized expanded beads were then loaded into a mold of a molding machine (EP-900L-M5, manufactured by DAISEN Co., Ltd.) measuring 370 mm in length, 320 mm in width, and 60 mm in thickness. The expanded beads were then heated for 5 to 10 seconds using heated steam at a pressure of 0.15 MPa (gauge pressure) to obtain a foamed molded article. The resulting foamed molded article was dried at 75°C and then left to stand for 24 hours in a constant temperature and humidity chamber at 23°C and 50% RH, after which the fusion properties of the foamed molded article were evaluated. The results are shown in Table 1.

[0100] [Examples 2 to 6, Comparative Examples 1 to 5] Expanded beads and expanded molded articles were produced and their physical properties were measured or evaluated in the same manner as in Example 1, except that the conditions of the cleaning liquid in step (B) were changed as shown in Table 1 or Table 2. The results are shown in Table 1 or Table 2.

[0101] Example 7 Expanded beads and expanded molded articles were produced in the same manner as in Example 1, except that the formulation (amount of dispersant) in step (A) was changed as shown in Table 1, and the physical properties were measured and evaluated. The results are shown in Table 1.

[0102] [Table 1]

[0103] [Table 2]

[0104] [Consideration] Examples 1 to 7 show that by washing the expanded beads with a washing solution that satisfies the conditions specified in one embodiment of the present invention, it is possible to provide expanded beads that both suppress mutual adhesion of the expanded beads during expansion and ensure fusibility when formed into an in-mold foamed article. Furthermore, it is also clear that, in particular, by setting the dispersant content of the expanded beads before washing to a certain level or higher, it is possible to provide expanded beads that are further suppressed from mutual adhesion.

[0105] On the other hand, Comparative Examples 1 to 5 show that when the expanded beads are washed with a cleaning liquid that does not satisfy the conditions specified in one embodiment of the present invention, the resulting expanded beads have poor fusion properties when made into a foamed molded article. [Industrial Applicability]

[0106] The expanded beads and foamed molded articles thereof provided by this production method can be suitably used in a variety of fields, including cushioning materials for packaging (e.g., cushioning materials for packaging home appliances such as refrigerators, freezers, air conditioner bodies and their outdoor units, washing machines, air purifiers, humidifiers, rice cookers, microwave ovens, ovens, toasters, electric fans, and storage battery units; and cushioning materials for packaging automobile items such as transmissions, roofs, hoods, doors, batteries, and engines), automobile components (e.g., bumper cores, headrests, luggage boxes, tool boxes, floor spacers, seat cores, child car seat cores, sun visor cores, and knee pads), heat insulating materials (e.g., containers for constant temperature storage and containers for constant temperature transportation), casting models, agricultural product boxes, fish boxes, building materials, and civil engineering materials.

Claims

1. A step (A) of expanding aliphatic polyester resin particles to obtain expanded aliphatic polyester particles; and (B) a step of washing the aliphatic polyester-based expanded beads with a washing liquid, The step (A) includes a dispersing step of dispersing the aliphatic polyester resin particles, an aqueous dispersion medium, a dispersant, and a blowing agent in a pressure-resistant container, In the step (B), the cleaning solution is an aqueous solution containing a water-soluble compound having, in the molecule thereof, at least one functional group capable of bonding to the dispersant and at least one hydrophilic functional group, The temperature of the cleaning liquid is 30°C to 95°C, The concentration of the water-soluble compound in the cleaning solution is 800 ppm to 70,000 ppm, and In the method for producing aliphatic polyester-based expanded beads, the amount of the cleaning liquid is 0.05 L to 0.50 L per 1 kg of the aliphatic polyester-based expanded beads.

2. 2. The method for producing expanded aliphatic polyester beads according to claim 1, wherein the dispersant is at least one selected from the group consisting of tricalcium phosphate, calcium carbonate, and magnesium carbonate.

3. The method for producing expanded aliphatic polyester beads according to claim 1, wherein the water-soluble compound is any one of a water-soluble phosphate, a water-soluble condensed phosphate, and a mixture thereof.

4. 2. The method for producing expanded aliphatic polyester beads according to claim 1, wherein the water-soluble compound is sodium hexametaphosphate.

5. 2. The method for producing aliphatic polyester-based expanded beads according to claim 1, wherein the step (B) further comprises a step of washing the aliphatic polyester-based expanded beads after washing with the washing liquid with an aqueous solution having a concentration of the water-soluble compound of 0 ppm to 5 ppm.

6. 6. The method for producing aliphatic polyester-based expanded beads according to claim 5, wherein the amount of the aqueous solution having a concentration of the water-soluble compound of 0 ppm to 5 ppm is 0.1 L to 1.0 L per 1 kg of the aliphatic polyester-based expanded beads.

7. 2. The method for producing expanded aliphatic polyester beads according to claim 1, wherein the expanded aliphatic polyester beads obtained in step (A) contain 2500 ppm to 5000 ppm of the dispersant.

8. 2. The method for producing expanded aliphatic polyester beads according to claim 1, wherein the expanded aliphatic polyester beads obtained in step (B) contain 1500 ppm or less of a dispersant.

9. A method for producing an aliphatic polyester-based expanded molded article, comprising a step of molding the expanded aliphatic polyester-based beads obtained by the method for producing expanded aliphatic polyester-based beads according to any one of claims 1 to 8.

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