Aliphatic polyester resin foam particles and method for manufacturing aliphatic polyester resin foam particles

Abstract

To provide aliphatic polyester-based resin foam particles that make it possible to provide a foamed particle compact excellent in both of secondary expandability, fusibility and recovery property during in-mold molding, in a wide range of molding pressure and a manufacturing method of aliphatic polyester-based resin foam particles.SOLUTION: Aliphatic polyester-based resin foam particles use an aliphatic polyester-based resin as a base resin, contain a gel content of 5 wt.% or more and 70 wt.% or less, and have a swelling degree of 3500 wt.% or more and 6000 wt.% or less when the gel content is swollen with cyclohexanone. According to a manufacturing method of aliphatic polyester-based resin foam particles, the aliphatic polyester-based resin having a weight average molecular weight (Mw) of 100,000 or more to 190,000 or less, and a ratio (Mw / Mn) of a weight average molecular weight (Mw) to a number average molecular weight (Mn) of 5 or more and 15 or less is kneaded, and obtained resin particles are crosslinked with an organic peroxide in an aqueous medium in a closed container, and the resin particles are foamed to obtain foamed particles, and the foamed particles contain the gel content of 5 wt.% or more and 70 wt.% or less.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to aliphatic polyester resin foam particles and a method for producing aliphatic polyester resin foam particles. [Background technology]

[0002] Foamed particle molded articles, possessing excellent characteristics such as lightness, elasticity, cushioning properties, and moldability, are widely used in various fields. Examples of applications for foamed particle molded articles include packaging containers and cushioning materials.

[0003] In recent years, awareness of the natural environment has increased, and efforts toward the Sustainable Development Goals (SDGs) have become active in various technological fields. Research and proposals from these perspectives are also being made in the field of foamed particle molding technology, and as one such effort, the use of biodegradable plastics that decompose in the natural environment is being researched.

[0004] More specifically, Patent Document 1 proposes aliphatic polyester resin foam particles having a cross-linked structure that is biodegradable and has a gel fraction of at least 5%. It is explained that these aliphatic polyester resin foam particles exhibit the effects of being biodegradable and having a low molding shrinkage rate.

[0005] Furthermore, Patent Document 2 proposes polyester resin foam particles that have been improved by widening the molding temperature range by making the chloroform-insoluble content inside the foam particles 20% by weight or more. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 10-324766 [Patent Document 2] Japanese Patent Publication No. 2001-49021 [Overview of the project] [Problems that the invention aims to solve]

[0007] The conventional foamed particles made using the aliphatic polyester resin described above still had room for further improvement. In other words, the aliphatic polyester resin foam particles described in Patent Document 1 have a narrow moldable range in which a good molded article can be obtained, and when molded at high temperatures, parts with a low crosslinking ratio sometimes occur in the crosslinking structure of the foam particles. As a result, the bubble film may rupture in the parts with a low crosslinking ratio, and large bubbles (voids) that are clearly different from the surrounding bubbles may occur inside the foam particles.

[0008] In contrast, the polyester resin foam particles described in Patent Document 2 have been improved to broaden the moldable range by adjusting the chloroform-insoluble content inside the foam particles to a favorable range. As a result, the polyester resin foam particles described in Patent Document 2 suppress the generation of voids inside as described above, but there was still room for further improvement regarding the moldable range.

[0009] The present invention has been made in view of the above problems, and provides aliphatic polyester resin foam particles and a method for producing aliphatic polyester resin foam particles that can provide a foam particle molded article with good secondary foaming properties, fusion properties, and recovery properties during in-mold molding over a wide molding pressure range. [Means for solving the problem]

[0010] The aliphatic polyester resin foam particles of the present invention are aliphatic polyester resin foam particles with an aliphatic polyester resin as the base resin, characterized in that the foam particles contain 5% to 70% by weight of gel content, and the degree of swelling when the gel content is swollen with cyclohexanone is 3500% to 6000% by weight.

[0011] Further, the method for producing expanded aliphatic polyester-based resin particles according to the present invention is a method for producing expanded aliphatic polyester-based resin particles, comprising: crosslinking resin particles obtained by kneading an aliphatic polyester-based resin with an organic peroxide in an aqueous medium in a closed container, and expanding the resin particles to obtain expanded particles, wherein the weight average molecular weight (Mw) of the aliphatic polyester-based resin is 100000 or more and 190000 or less, the ratio of the weight average molecular weight (Mw) to the number average molecular weight (Mn) of the aliphatic polyester-based resin (Mw / Mn) is 5 or more and 15 or less, and the expanded particles contain a gel content of 5% by weight or more and 70% by weight or less Furthermore, the degree of swelling when the gel component is swollen with cyclohexanone is 3500% by weight or more and 6000% by weight or less. . Effects of the Invention

[0012] According to the expanded aliphatic polyester-based resin particles of the present invention, an expanded particle molded article having excellent secondary foamability, fusion bonding property and recovery property all during in-mold molding over a wide molding pressure range can be provided.

[0013] Further, the method for producing expanded aliphatic polyester-based resin particles according to the present invention can produce expanded aliphatic polyester-based resin particles that all have excellent secondary foamability, fusion bonding property and recovery property during in-mold molding, and can widen the moldable range during in-mold molding. Mode for Carrying Out the Invention

[0014] Hereinafter, the aliphatic polyester resin expanded beads and a method for producing the aliphatic polyester resin expanded beads will be described in order. Note that, hereinafter, the aliphatic polyester resin expanded beads of the present invention may be simply referred to as the expanded beads of the present invention, and the method for producing the aliphatic polyester resin expanded beads of the present invention may be simply referred to as the production method of the present invention. Also, in the context of the present invention, the moldable range means the range of molding pressure within which an expanded bead molded article having good secondary foamability, good fusion-bonding property and good restorability can all be produced by in-mold molding. In the context of the present invention, a wide moldable range means that the range between the upper limit molding pressure and the lower limit molding pressure (i.e., the difference therebetween) at which a good expanded bead molded article can be obtained during in-mold molding using the expanded beads is wide, and as a result, a good expanded bead molded article can be easily obtained. That is, a wide moldable range means a wide molding pressure range. Also, the gel content of the expanded beads of the present invention refers to the gel content (cyclohexanone-insoluble content) in the expanded beads measured by a specific method described later using the expanded beads, and in the context of the present invention, the gel fraction refers to the proportion of the gel content contained in 100% by weight of the expanded beads.

[0015] Aliphatic Polyester Resin Expanded Beads The expanded beads of the present invention are aliphatic polyester resin expanded beads using an aliphatic polyester resin as a base resin. The expanded beads of the present invention contain a gel content of 5 wt% or more and 70 wt% or less, and the degree of swelling when the gel content is swollen with cyclohexanone is 3500 wt% or more and 6000 wt% or less. The expanded beads of the present invention having such a configuration exhibit a wider moldable range than conventional expanded beads in in-mold molding. In other words, according to the present invention, it is possible to obtain an expanded bead molded article having good secondary foamability, good fusion-bonding property and good restorability during in-mold molding over a wide moldable range. Hereinafter, the expanded beads of the present invention will be described in detail.

[0016] The foamed particles of the present invention use a biodegradable aliphatic polyester resin as the base resin. Using an aliphatic polyester resin as the base resin for the foamed particles of the present invention means that, in 100% by weight of the resin constituting the foamed particles of the present invention, the aliphatic polyester resin is contained in an amount exceeding 50% by weight. From the viewpoint of biodegradability, the aliphatic polyester resin content is preferably 70% by weight or more, more preferably 90% by weight or more, and can be substantially 100% by weight. However, the foamed particles of the present invention may also contain other materials such as resins other than aliphatic polyester resin or various additives, as long as they do not impair the purpose and effects of the present invention.

[0017] The above aliphatic polyester resins include polymers of glycol components and dicarboxylic acid components, hydroxy acid polymers, and ring-opening polymers of lactide. One type of aliphatic polyester may be used alone, or two or more types may be used in combination. Examples of polymers of glycol components and dicarboxylic acid components include polybutylene succinate, polybutylene succinate adipate, polyethylene succinate, polyhexamethylene succinate, polyethylene adipate, polyhexamethylene adipate, polybutylene adipate, polyethylene oxalate, polybutylene oxalate, polyneopentyl oxalate, polyethylene sebacate, polybutylene sebacate, and polyhexamethylene sebacate. Examples of hydroxy acid polymers include polymers of hydroxybutyric acid. Examples of ring-opening polymers of lactide include polylactide. In particular, from the viewpoint of successfully solving the intended problems of the present invention, the above aliphatic polyester resin is preferably a polymer of a glycol component and a dicarboxylic acid component, and more preferably a polymer having a 1,4-butanediol component and succinic acid and / or adipic acid component. When a polymer having a 1,4-butanediol component and succinic acid and / or adipic acid component is used as the above aliphatic polyester resin, by keeping the amount of structural units derived from succinic acid within a predetermined range, appropriate biodegradability can be achieved when used in applications where rapid decomposition after use is required. From the above viewpoint, the proportion of structural units derived from succinic acid in the total dicarboxylic acid units is preferably 50 mol% or more and 100 mol% or less, more preferably 80 mol% or more and 100 mol% or less, and even more preferably 90 mol% or more and 100 mol% or less. From the above viewpoint, the above aliphatic polyester resin is particularly preferably polybutylene succinate, which is a polymer of a 1,4-butanediol component and a succinic acid component. Note that copolymers are also included in the above polymer.

[0018] The foamed particles of the present invention contain a gel content in the range of 5% to 70% by weight. If the gel content is too low, the upper limit molding pressure will be low, which may result in a narrower moldable range. Also, if the gel content is too low, some of the air bubbles in the foamed particles may rupture and shrink during in-mold molding, which may prevent the acquisition of a good foamed molded product. From these viewpoints, the gel content in the foamed particles of the present invention is preferably 10% by weight or more, and more preferably 20% by weight or more. On the other hand, if the gel content is too high, the lower limit molding pressure will be high, which may result in a narrower moldable range. Also, if the gel content is too high, the secondary foaming properties of the foamed particles may decrease during in-mold molding, which may reduce the fusion properties between the foamed particles. From these viewpoints, the gel content in the foamed particles of the present invention is preferably 50% by weight or less, and more preferably 40% by weight or less.

[0019] The gel fraction in the foamed particles of the present invention is measured by the following gel filtration and drying processes. [Gel filtration treatment] First, place approximately 0.25g of foaming particles (weight A) and 100ml of cyclohexanone into a 200ml round-bottom flask. Heat under atmospheric pressure using a heater for at least 8 hours under reflux to extract the cyclohexanone-soluble components from the foaming particles, obtaining a heat-treated product consisting of the cyclohexanone-insoluble components. Place an 80-mesh screen, whose weight has been measured in advance, into a funnel and filter the heat-treated product obtained as described above. Note that filtration should be performed until no droplets remain on the heat-treated product, for example, for about 1 minute. [Drying process] After the gel filtration treatment described above, the heat-treated material collected on the mesh is dried overnight at room temperature in a fume hood while still on the mesh. Then, it is placed in a vacuum oven and dried at 80°C for 3 hours or more to obtain a dried product. After the vacuum drying, the dried product is left at room temperature for 30 minutes or more, and then its weight is measured (Weight B).

[0020] Using the weights measured as described above, the gel fraction of the foamed particles is calculated using the following formula (1). [Mathematics 1] Gel fraction (weight %) = [weight B / weight A] × 100 ... (1)

[0021] The foamed particles of the present invention have a swelling degree of 3500% to 6000% by weight when the gel component is swollen with cyclohexanone. In this invention, swelling degree refers to the degree of swelling of the foamed particles when they are immersed in an organic solvent such as cyclohexanone. The inventors' studies have shown that when the swelling degree of the foamed particles is moderately high, the stretchability of the resin constituting the foamed particles is good, resulting in excellent secondary foaming during in-mold molding and an improved moldability of the foamed particle molded article. In the present invention, it was found that if the foamed particles have a sufficiently high gel fraction and exhibit the moderately high degree of swelling described above, the moldable range can be improved.

[0022] If the degree of swelling is too low, the moldable range may not be sufficiently improved. From this viewpoint, the degree of swelling is preferably 3700% by weight or more, more preferably 4000% by weight or more, and even more preferably 4200% by weight or more. On the other hand, if the degree of swelling is too high, the air bubbles of the foamed particles may burst and shrink during in-mold molding, making it difficult to obtain a molded product. From this viewpoint, the degree of swelling is preferably 5800% by weight or less, more preferably 5500% by weight or less, and even more preferably 5300% by weight or less.

[0023] The degree of swelling in this invention is measured as follows. The same process as the gel filtration treatment described above for measuring the gel fraction is performed, and the resulting heat-treated material, still on the mesh, is placed on an aluminum dish whose weight has been measured in advance. The weight of the heat-treated material (weight C) is then measured after subtracting the weight of the mesh and the aluminum dish. Then, using the weight B obtained from the drying process in the measurement of the gel fraction described above, the degree of swelling of the gel contained in the foamed particles is calculated using the following formula (2). [Math 2] Swelling degree (weight %) = [weight C / weight B] × 100 ... (2)

[0024] In the present invention, the ratio of swelling degree (weight%) to gel content (weight%) (swelling degree / gel fraction) is preferably 70 to 500, and more preferably 90 to 300. By having the above ratio (swelling degree / gel fraction) within the above range, it is possible to provide foamed particles with a sufficiently wide moldable range.

[0025] Furthermore, when determining whether or not a foamed particle has a sufficiently wide moldable range, the following formula (3) can serve as an indicator. That is, in order to obtain foamed particles with a wide moldable range, it is desirable to adjust the foamed particle so that it satisfies the following formula (3), which consists of the degree of swelling y and the gel fraction x. Moreover, according to the manufacturing method of the present invention described later, foamed particles that satisfy the following formula (3) are easily obtained. [Math 3] y≧-35x+4500·····(3)

[0026] The foamed particles of the present invention, having a gel fraction and swelling degree within a desirable range, tend to exhibit a high foaming ratio. For example, the bulk density of the foamed particles of the present invention is 25 kg / m³. 3 More than 60kg / m 3 The following is preferable; in other words, foamed particles with such bulk density can be easily obtained in the present invention. The foamed particles of the present invention can exhibit the above range of bulk density without, for example, undergoing a two-stage foaming process. A two-stage foaming process refers to a process of further foaming foamed particles produced by foaming resin particles.

[0027] The foamed particles of the present invention are preferably composed of an aliphatic polyester resin having a weight-average molecular weight (Mw) of 100,000 or more and 190,000 or less. Furthermore, the foamed particles of the present invention are preferably composed of an aliphatic polyester resin having a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) of 5 or more and 15 or less. Foamed particles using an aliphatic polyester resin as the base resin exhibiting the above-mentioned weight-average molecular weight (Mw) and ratio (Mw / Mn) are preferable because the gel fraction is in the range of 5% to 70% by weight, and the degree of swelling is easily adjustable to 3500% to 6000% by weight.

[0028] The foamed particles of the present invention contain an aliphatic polyester resin as a base resin, and may further optionally contain other resins or additives. The other resins are appropriately selected from resins or elastomers suitable for constituting the foamed particles, without departing from the spirit of the present invention. However, from the viewpoint of providing biodegradable foamed particles, it is preferable that the other resins are also biodegradable resins, and it is more preferable that they are biomass-derived biodegradable resins. Examples of additives include colorants, bubble nucleating agents, foaming aids, antioxidants, bubble regulators, antistatic agents, ultraviolet absorbers, and flame retardants. Colorants are additives for coloring the foamed particles to black, gray, brown, etc., and examples include coloring pigments or dyes. As coloring pigments, it is preferable to use carbon-based pigments such as carbon black, graphite and carbon fiber, metal-based pigments such as iron oxide, and organic pigments such as aniline black. Examples of bubble nucleating agents include talc, calcium carbonate, borax, zinc borate, aluminum hydroxide, and silica. Examples of foaming aids include magnesium stearate. Examples of antioxidants include phenolic antioxidants such as hindered phenolic antioxidants, sulfuric antioxidants, and phosphorus-based antioxidants. Phenolic antioxidants are preferred, and hindered phenolic antioxidants are even more preferred. The other resins and optional additives mentioned above are preferably present in amounts of 0.001 parts by weight or more and 5 parts by weight or less per 100 parts by weight of the base resin.

[0029] Fluorine-based resins can also be used as the foam nucleating agent. Furthermore, it is preferable to use the fluorine-based resin in combination with a fatty acid metal salt used as a foaming aid. When fluorine-based resins and fatty acid metal salts are used in combination, the secondary foaming properties of the foam particles can be improved, and the moldable period of the foam particles can be extended. Here, the moldable period refers to the period during which good moldable products can be obtained when the foam resin particles are stored at 40°C and 80% RH after production. Examples of the above-mentioned fluororesins include resins containing fluorine atoms, specifically polytetrafluoroethylene, polychlorotrifluoroethylene, polyvinylidene fluoride, polyvinyl fluoride, perfluoroalkoxy fluororesins, tetrafluoroethylene-hexafluoropropylene copolymer, ethylene-tetrafluoroethylene copolymer, and ethylene-chlorotrifluoroethylene copolymer. From the viewpoint of dispersibility in the resin, polytetrafluoroethylene is preferably used as the above-mentioned fluororesin. Furthermore, examples of fatty acid metal salts include salts of fatty acids such as stearic acid, lauric acid, ricinoleic acid, and octic acid with metals such as calcium, magnesium, barium, zinc, iron, and copper. Preferably, calcium stearate, calcium stearate, and magnesium stearate are used. Furthermore, the amount of fluororesin added is preferably 0.01% to 0.8% by weight, more preferably 0.03% to 0.5% by weight, and even more preferably 0.05% to 0.4% by weight, based on 100% by weight of resin particles. If the amount of fluororesin added is within the above range, the foaming efficiency will be increased, and foam particles with appropriate bubble diameters will be obtained with less variation in the foaming ratio of each foam particle. As a result, recovery during molding can be maintained even at high molding pressures, and consequently the molding range will be widened. On the other hand, the amount of fatty acid metal salt added is preferably 0.01% to 0.8% by weight, more preferably 0.03% to 0.5% by weight, and even more preferably 0.06% to 0.4% by weight, per 100% by weight of resin particles. If the amount of fatty acid metal salt added is within the above range, the foaming efficiency will be increased, the variation in foaming ratio between foamed particles will be reduced, and foamed particles with suppressed variation in bubble diameter will be obtained. This will improve secondary foaming at low molding pressure and broaden the molding range. Furthermore, the ratio of the amount of fatty acid metal salt added to the amount of fluororesin added per 100% by weight of resin particles is preferably 0.1 to 5, more preferably 0.4 to 2, and even more preferably 0.5 to 1.5, from the viewpoint of processability during foaming and moldability. If the ratio of the amount of fatty acid metal salt added to the amount of fluororesin added is within the above range, the foaming efficiency becomes particularly high, the variation in foaming ratio for each foamed particle is reduced, and foamed particles with suppressed variation in bubble diameter are more easily obtained. As a result, secondary foaming performance at low molding pressure is improved, while recovery during molding can be maintained even at high molding pressure, so that the foamed particles have a wide molding range.

[0030] [Method for manufacturing aliphatic polyester resin foam particles] Next, the manufacturing method of the present invention will be described. The manufacturing method of the present invention is a preferred embodiment of the manufacturing method of the foamed particles of the present invention. However, the method for manufacturing the foamed particles of the present invention is not limited in any way to the manufacturing method of the present invention.

[0031] The present invention relates to a method for producing foamed aliphatic polyester resin particles, which are obtained by kneading an aliphatic polyester resin to form resin particles, crosslinking these particles with an organic peroxide in an aqueous medium in a sealed container, and foaming the resin particles to obtain foamed particles. The aliphatic polyester resin used in the present invention has a weight-average molecular weight (Mw) of 100,000 to 190,000, and a ratio of weight-average molecular weight (Mw) to kalc-average molecular weight (Mn) (Mw / Mn) of 5 to 15. The foamed particles produced by the present invention are characterized by containing 5% to 70% by weight of gel. According to the manufacturing method of the present invention having the above configuration, aliphatic polyester resins are crosslinked with high crosslinking efficiency, thereby producing foamed particles containing a large amount of gel. When in-mold molding is performed using such foamed particles, it is possible to produce a foamed particle molded article with excellent secondary foaming properties, fusion properties, and recovery properties, and such a good foamed particle molded article can be obtained over a wide molding pressure range. In relation to the present invention, crosslinking efficiency is calculated by dividing the gel fraction (weight %) of the produced foamed particles by the amount of crosslinking agent added in the production (amount added per 100 parts by weight of resin particles). The manufacturing method of the present invention will be described in detail below.

[0032] To produce the foamed particles of the present invention, first, resin particles made using an aliphatic polyester resin are prepared. These particles can be made by conventionally known methods, for example, by melt-kneading an aliphatic polyester resin in an extruder, extruding it into strands, cooling it, and then cutting it to an appropriate length, or by cutting the strands to an appropriate length and then cooling them. The weight of each resin particle is preferably 0.05 mg to 10 mg, more preferably 0.5 mg to 4 mg, and even more preferably 1 mg to 3 mg. It is preferable that the particle weight satisfies the above range because it allows for easy crosslinking to the interior of the resin particles, making it easier to obtain foamed particles with homogeneous crosslinking on the surface and inside.

[0033] In the manufacturing method of the present invention, the weight-average molecular weight (Mw) of the aliphatic polyester resin used is preferably 100,000 to 190,000, and more preferably 150,000 to 180,000. Furthermore, the aliphatic polyester resin used has a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) of 5 to 15, and preferably a ratio of weight-average molecular weight (Mw) to number-average molecular weight (Mn) (Mw / Mn) of 8 to 13. By using an aliphatic polyester resin that satisfies these conditions, foamed particles with a swelling degree of 3,500% to 6,000% by weight when swollen with cyclohexanone are easily obtained. For example, if the above-mentioned ratio (Mw / Mn) is less than 5, there is a risk that foamed particles with a swelling degree below 3,500% by weight and a narrow moldable range will be produced.

[0034] The weight-average molecular weight (Mw) and number-average molecular weight (Mn) of aliphatic polyester resins can be measured by gel permeation chromatography (GPC) using polystyrene as the standard substance. Specifically, first, 30 mg of aliphatic polyester resin is dissolved in 20 mL of chloroform to obtain a solution. If insoluble matter is present in the solution, it is removed by filtration. Then, using this solution, GPC measurements are performed under the analytical conditions shown below. A horizontal baseline is drawn based on the peak start position for the aliphatic polyester resin in the chart obtained from this measurement, and each molecular weight is calculated using a standard calibration curve created with standard polystyrene. Here, "horizontal" means parallel to the horizontal axis of the chart. Measuring device: 2695, manufactured by Waters Japan Co., Ltd. Column: TSK Gel G5000H manufactured by Tosoh Corporation HR and TSK Gel G3000H manufactured by Tosoh Corporation HR Connect them in series in this order and use them. Column temperature: 40℃ Solvent: Chloroform Flow rate: 1.0mL / min Concentration: 0.4w / v% Injection volume: 100μl Detector: Manufactured by Waters Japan Ltd., model number 2414 Molecular weight conversion: Molecular weight range of the calibration curve used to calculate the molecular weight distribution in polystyrene (PS): 500 to 3,787,000

[0035] Furthermore, the melt flow rate (test temperature 190°C, nominal load 2.16 kg) of the aliphatic polyester resin used in the production of the resin particles is preferably 4 g / 10 min to 20 g / 10 min, and more preferably 5 g / 10 min to 10 g / 10 min. If foamed particles are produced using an aliphatic polyester resin exhibiting the above melt flow rate range, the degree of swelling when the gel component in the foamed particles is swollen with cyclohexanone can be easily adjusted to a range of 3500% to 6000% by weight. The melt flow rate of aliphatic polyester resins is measured according to JIS K7210-1:2014, under conditions of a test temperature of 190°C and a nominal load of 2.16 kg.

[0036] The aliphatic polyester resin used in the production of resin particles preferably has a biomass content of 10% by weight or more, more preferably 25% by weight or more, and even more preferably 40% by weight or more, in accordance with ASTM D6866-21. The upper limit of the biomass content of the above aliphatic polyester resin is 100% by weight. Aliphatic polyester resins that satisfy the above biomass content are preferred because they contribute to reducing environmental impact. In this invention, "biomass content" refers to the weight ratio of biomass-derived components.

[0037] The above-mentioned resin particles may optionally contain other resins or additives in addition to aliphatic polyester resins. For information on other resins and additives, please refer to the description of other resins or additives that may be included in the foamed particle body described above. For example, foam nucleating agents, foaming aids, and antioxidants are preferably used optional components.

[0038] In particular, resin particles obtained by kneading an aliphatic polyester resin together with a phenolic antioxidant are preferably used in the manufacturing method of the present invention. The amount of phenolic antioxidant added is preferably 0.0005% to 0.08% by weight, and more preferably 0.0008% to 0.05% by weight, based on 100% by weight of the resin particles. When a phenolic antioxidant is added to an aliphatic polyester resin within this range, the self-crosslinking of the resin is appropriately suppressed when the resin constituent material is melt-kneaded and then extruded into strands to form pellets, preventing the viscosity of the resin from increasing too much. Furthermore, when the resin particles contain a phenolic antioxidant within a desirable range, the foamed particles made using these resin particles tend to exhibit excellent recovery during in-mold molding and a sufficiently wide moldability range.

[0039] Next, a crosslinking process is carried out to crosslink the pre-prepared resin particles. In this crosslinking process, the resin particles are first dispersed in an aqueous medium in a sealed container. To prevent the resin particles from fusing together in the aqueous medium and to ensure good dispersion, a dispersant may be added to the aqueous medium as appropriate, and a dispersion aid may also be used. The above-mentioned aqueous medium can be any aqueous dispersion medium that can disperse resin particles in a sealed container. Examples include water, ethylene glycol, methanol, and ethanol, but water is usually used. The above dispersant can be inorganic or organic as long as it does not dissolve in an aqueous medium and does not melt when heated, but an inorganic one is preferred. Suitable inorganic dispersants include powders such as aluminum oxide, kaolin, mica, talc, tricalcium phosphate, magnesium oxide, magnesium carbonate, and magnesium hydroxide. The amount of the above dispersant added is usually in the range of 0.01 parts by weight to 10 parts by weight per 100 parts by weight of resin particles. Furthermore, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium oleate can be suitably used as dispersing aids. The amount of the above-mentioned dispersing aid added is preferably in the range of 0.001 parts by weight to 5 parts by weight per 100 parts by weight of resin particles.

[0040] The timing of adding the crosslinking agent to the sealed container for crosslinking the resin particles is not particularly limited, but for example, it can be added at the same time as the resin particles are dispersed in the aqueous medium in the sealed container. Furthermore, additional crosslinking aids may be added as appropriate. In the manufacturing method of the present invention, an organic peroxide is used as a crosslinking agent. Examples of organic peroxides that can be used include diacyl peroxides such as lauroyl peroxide, stearoyl peroxide, and benzoyl peroxide; peroxydicarbonates such as bis(4-t-butylcyclohexyl) peroxydicarbonate and diisopropyl peroxydicarbonate; and peroxyesters such as t-butyl peroxyisobutyrate. Among these, benzoyl peroxide is preferably used in the manufacturing method of the present invention because the temperature at which it gives a half-life of 1 hour is near the softening temperature of the base resin and lower than its melting point, and it can crosslink aliphatic polyester resins well while suppressing hydrolysis of the base resin. From the viewpoint of easily obtaining foamed particles that contain the desired gel component and whose degree of swelling of the gel component is within a predetermined range, the amount of organic peroxide used as a crosslinking agent added is preferably in the range of 0.01 parts by weight or more and 1 part by weight or less, more preferably in the range of 0.03 parts by weight or more and 0.5 parts by weight or less, and even more preferably in the range of 0.05 parts by weight or more and 0.25 parts by weight or less, per 100 parts by weight of resin particles.

[0041] By using a crosslinking aid together with the above-mentioned organic peroxide, which is the crosslinking agent, it is easy to adjust the proportion of gel content (cyclohexanone-insoluble content) in the manufactured foamed particles to a high level. The above-mentioned crosslinking aid is preferably a compound having at least one unsaturated bond in its molecule, and preferably a compound having at least two, more preferably two to three, unsaturated bonds. In this case, the unsaturated bonds include not only double bonds but also triple bonds. Crosslinking aids include divinyl compounds such as divinylbenzene; acrylic acid, methacrylic acid; acrylic acid esters such as methyl acrylate and ethyl acrylate; methacrylic acid esters such as methyl methacrylate and ethyl methacrylate; styrene, vinyl acetate; acrylate or methacrylate compounds such as ethylene glycol diacrylate, polyethylene glycol diacrylate, trimethylolpropane triacrylate, tetramethylolmethane triacrylate, tetramethylolmethane tetraacrylate, ethylene glycol dimethacrylate, trimethylolpropane trimethacrylate, allyl methacrylate, glycidyl methacrylate; and triallyl methyl acrylate. Examples of compounds include allyl esters of cyanuric acid or isocyanuric acid such as anurate and triallyl isocyanurate; allyl esters of carboxylic acids such as trimellitrotriyl ester, trimesic acid trialyl ester, pyromellitic acid trialyl ester, benzofenonetetracarboxylic acid trialyl ester, diallyl oxalate, diallyl succinate, and diallyl adipate; maleimide compounds such as N-phenylmaleimide and N,N'-m-phenylenebismaleimide; polymers having double bonds such as 1,2-polybutadiene; and compounds such as dipropagyl phthalate, dipropagyl isophthalate, tripropagyl trimesic acid, dipropagyl itaconic acid, and dipropagyl maleate. In the present invention, combinations of organic peroxides with divinyl compounds or methacrylate esters are preferred, particularly combinations of benzoyl peroxide with divinylbenzene or methyl methacrylate. The amount of unsaturated compound used as a crosslinking aid is preferably in the range of 0.001 parts by weight or more and 10 parts by weight or less per 100 parts by weight of resin particles, more preferably in the range of 0.005 parts by weight or more and 5 parts by weight or less, and even more preferably in the range of 0.01 parts by weight or more and 2 parts by weight or less.

[0042] In the crosslinking process, resin particles are dispersed in a dispersion medium within a sealed container, and the contents of the sealed container are heated to crosslink the aliphatic polyester resin constituting the resin particles. The heating temperature during crosslinking is difficult to determine uniquely depending on the type of resin constituting the resin particles, but generally, it is a temperature at or above approximately 60°C lower than the melting point of the resin. For example, if the resin constituting the resin particles is a polyester resin consisting of a 1,4-butanediol component and a succinic acid component and / or an adipic acid component (melting point: 113°C), the heating temperature is 50°C to 140°C, preferably 90°C to 120°C.

[0043] Furthermore, before reaching a temperature suitable for crosslinking, a crosslinking agent impregnation step may be performed to impregnate the resin particles with organic peroxide as needed. The crosslinking agent impregnation step involves adding resin particles and crosslinking agents to a dispersion medium and heating the inside of a sealed container at a temperature lower than the temperature required for the crosslinking step for a predetermined time to impregnate the resin particles with organic peroxide. After the crosslinking agent impregnation step, the crosslinking step is performed by raising the temperature to a temperature suitable for the crosslinking step and heating for a predetermined time.

[0044] The manufacturing method of the present invention involves performing a foaming step at a timing that partially overlaps with the crosslinking step described above, or after the completion of the crosslinking step described above. This makes it possible to obtain foamed particles containing a predetermined range of gel content. Specifically, the foaming process involves dispersing resin particles in a dispersion medium within a sealed container, heating the contents of the container to impregnate them with a foaming agent, then opening one end of the sealed container, and simultaneously releasing the resin particles and dispersion medium into a lower-pressure atmosphere (usually atmospheric pressure) while maintaining the internal pressure at a level greater than or equal to the vapor pressure of the foaming agent, thereby causing foaming. Other foaming methods include impregnating resin particles with a foaming agent in a sealed container to obtain foamable particles, removing them from the container, and then heating and softening them to cause foaming; or pre-mixing a decomposition-type foaming agent into the resin particles and then heating the resin particles to a temperature above the decomposition temperature of the foaming agent to cause foaming.

[0045] As blowing agents used in the above foaming process, conventionally known volatile blowing agents such as propane, butane, hexane, cyclobutane, cyclohexane, trichlorofluoromethane, dichlorodifluoromethane, chlorofluoromethane, trifluoromethane, 1,2,2,2-tetrafluoromethane, 1-chloro-1,1-difluoroethane, 1,1-difluoroethane, and 1-chloro-1,2,2,2-tetrafluoroethane, as well as inorganic gas blowing agents such as nitrogen, carbon dioxide, argon, and air, are used. Among these, inorganic gas blowing agents that do not deplete the ozone layer and are inexpensive are preferred, and nitrogen, carbon dioxide, or air are particularly preferred.

[0046] In the foaming process, the amount of foaming agent used should be injected into a sealed container under pressure to maintain a pressure range of 2 MPa(G) to 6 MPa(G). In this specification, pressures denoted by (G) are gauge pressures, i.e., pressures relative to atmospheric pressure. The amount of foaming agent used is appropriately selected based on the relationship between the desired bulk density of the foamed particles and the foaming temperature.

[0047] The heating temperature used to impregnate the resin particles with the foaming agent is preferably around the softening temperature of the resin particles. Therefore, if the heating temperature in the crosslinking process is around the softening temperature of the resin particles, the foaming agent can be impregnated into the resin particles in overlap with the crosslinking process. After impregnating the resin particles with the foaming agent, it is advisable to adjust the temperature of the contents of the sealed container to be approximately 5°C to 15°C lower than the temperature at which the foaming agent was impregnated, in order to prevent the particles from fusing together during foaming, before releasing the resin particles and dispersion medium to the outside of the sealed container.

[0048] As described above, the manufacturing method of the present invention can produce foamed particles containing 5% to 70% by weight of gel through a crosslinking step and a foaming step. Such foamed particles exhibit the excellent effects of the foamed particles of the present invention described above.

[0049] In the manufacturing method of the present invention, in the crosslinking step described above, the resin particles are sufficiently crosslinked by heating in the presence of a crosslinking agent in the dispersion medium, thereby obtaining foamed particles containing gel content in the range of 5% to 70% by weight. If the gel content of the resulting foamed particles falls below the range described above, the recovery properties of the foamed molded article formed using these particles will decrease, making it impossible to obtain a practical foamed molded article. On the other hand, foamed particles with a gel content higher than the range described above may have poor secondary foaming and fusing properties, making it impossible to obtain a high-quality foamed molded article. The gel content of the foamed particles can be adjusted, for example, by the crosslinking conditions when crosslinking resin particles in the presence of a crosslinking agent in a dispersion medium.

[0050] Furthermore, it is preferable that the foamed particles obtained by the manufacturing method of the present invention have a swelling degree of 3500% by weight or more and 6000% by weight or less when the gel component contained in the foamed particles is swollen with cyclohexanone. Foamed particles whose swelling degree satisfies the above range have a wide moldable range, making it easier to obtain a good foamed particle molded article.

[0051] The bulk density of the foamed particles obtained by the manufacturing method of the present invention is 25 kg / m³. 3 More than 60kg / m 3 The following is preferable. In other words, according to the manufacturing method of the present invention, by simply carrying out the crosslinking process and foaming process described above, without requiring a two-stage foaming process, etc., 25 kg / m 3 More than 60kg / m3 It is possible to produce expanded particles having a bulk density within the following range. An expanded particle molded article produced by in-mold molding using expanded particles exhibiting such a bulk density is excellent in light weight and is suitably used in various application fields. Although the reason why expanded particles having a low bulk density can be produced as described above is not clear, when an aliphatic polyester resin having a weight average molecular weight (Mw) of 100,000 or more and 190,000 or less and a ratio (Mw / Mn) of weight average molecular weight (Mw) to number average molecular weight (Mn) of 5 or more and 15 or less is used, and the gel content of the expanded particles produced by the production method of the present invention is in the range of 5% by weight or more and 70% by weight or less, it is considered that the above-mentioned expanded particles having a low bulk density are easily obtained. Further, it is considered that when expanded particles having a swelling degree of 3500% by weight or more and 6000% by weight or less when the gel content is swollen with cyclohexanone are produced, the above-mentioned expanded particles having a low bulk density are more easily obtained.

[0052] The bulk density is determined as follows. Expanded particles to be measured are left to stand for curing for 24 hours or more in an environment of 23°C air temperature, 50% relative humidity, and 1 atm. The cured expanded particle group (weight W; 30 g) is filled into a graduated cylinder, and the bottom of the graduated cylinder is lightly tapped against the floor several times to stabilize the filling height of the expanded particle group in the graduated cylinder. Then, the bulk volume V (L) of the expanded particle group indicated by the scale of the graduated cylinder is read, and the weight W of the expanded particle group is divided by the bulk volume V (W / V). The value thus obtained is converted to the unit kg / m 3 to convert the unit, thereby obtaining the bulk density (kg / m 3 ) of the expanded particles.

[0053] The production method of the present invention has been described above, but the production method of expanded particles of the present invention is not limited thereto. For example, in the production method of the present invention, a method including a crosslinking step of crosslinking resin particles with an organic peroxide has been described, but the expanded particles of the present invention are not limited to the crosslinking step using an organic peroxide, and can be produced by crosslinking and expanding using other known crosslinking methods, such as electron beam crosslinking, silane crosslinking, and the like.

[0054] To manufacture a molded foam particle article using the foam particles of the present invention, an in-mold molding method is generally employed. Specifically, the foam particles are placed in a mold and heated. This heating causes the foam particles to fuse together, resulting in a unified foamed molded article. Conventional molds are used for molding in this case. Steam heating is usually used as the heating method, and the heating temperature should be such that the surface of the foam particles melts. By using the foam particles of the present invention, the moldable range during in-mold molding is widened, making it possible to provide a molded foam particle article with excellent secondary foaming properties, fusion properties, and recovery properties, even in complex shapes.

[0055] The foamed particle molded article produced using the foamed particles of the present invention has a yield of 25 kg / m³. 3 More than 70kg / m 3 The molded article may exhibit a density with excellent lightweight properties within the following range.

[0056] The present invention includes foamed particles obtained by carrying out a two-stage foaming process to obtain foamed particles having desired physical properties, and a method for producing the same. That is, the foamed particles of the present invention include two-stage foamed particles obtained by a two-stage foaming process. The manufacturing method of the present invention also includes a method in which the foamed particles obtained by the manufacturing method of the present invention described above are treated as single-stage foamed particles, and a two-stage foaming process is carried out using these single-stage foamed particles to produce two-stage foamed particles with a lower bulk density than the single-stage foamed particles. Here, the two-stage foaming process is a process in which the single-stage foamed particles produced as described above are supplied to a pressure vessel, a foaming agent such as air is injected into the pressure vessel to increase the internal pressure in the bubbles of the single-stage foamed particles, and the particles are heated with steam or the like to cause foaming. In particular, when fluororesins and fatty acid metal salts are used in combination, the secondary foaming properties of the foamed particles can be improved, so that even when foamed particles are obtained by a two-stage foaming process, the foamed particles will have good moldability. In other words, the present invention can provide foamed particles and molded foamed particle articles that exhibit excellent lightweight properties while maintaining good moldability by implementing a two-stage foaming process. In this invention, the bulk density of the foamed particles (secondary foamed particles) obtained by carrying out a two-stage foaming process is 10 kg / m³.3 More than 25kg / m 3 The bulk density can be adjusted as follows, and from the viewpoint of lightweight properties, it is preferable that the bulk density be within the range described above. Furthermore, the molded density of a foam particle molded body formed in a mold using such foam particles is 10 kg / m³. 3 More than 25kg / m 3 The following is preferable: [Examples]

[0057] The present invention will be described in detail below with reference to examples. In these examples, foamed particles were produced by carrying out the manufacturing method of the present invention. However, the present invention is not limited thereto. Furthermore, for the foamed particles of each example and comparative example obtained as described below, the bulk density, gel fraction, and degree of swelling were measured, and the crosslinking efficiency was determined. In addition, in-mold molding was performed using the above foamed particles, and the lower and upper limits of the molding pressure were confirmed, thereby determining the moldable range. Furthermore, the density of the molded articles produced by in-mold molding using the foamed particles of each example and comparative example was measured. The results of the above measurements are shown in Tables 1 to 3.

[0058] <Example 1> As an aliphatic polyester resin, polybutylene succinate resin (Bio-PBS-FZ91PB, manufactured by PTT MCC Biochem CO.Ltd, with a biomass content of 50%) was prepared, and its number-average molecular weight (Mn), weight-average molecular weight (Mw), melt flow rate (MFR), and biomass content were measured as follows. (Methods for measuring number-average molecular weight (Mn) and weight-average molecular weight (Mw)) As a pretreatment, 30 mg of aliphatic polyester resin was dissolved in 20 mL of chloroform to obtain a solution. This solution was filtered through a syringe filter with a pore size of 0.45 μm, and the resulting filtrate was used as the analytical sample. The number-average molecular weight (Mn) and weight-average molecular weight (Mw) were measured by gel permeation chromatography under the following conditions. Measuring device: 2695, manufactured by Waters Japan Co., Ltd. Column: TSK Gel G5000H manufactured by Tosoh Corporation HR and Tosoh Corporation's G3000H HR Connect them in series in this order and use them. Column temperature: 40℃ Solvent: Chloroform Flow rate: 1.0mL / min Concentration: 0.4w / v% Injection volume: 100μl Detector: 2414, manufactured by Waters Japan Ltd. Molecular weight conversion: Molecular weight range of the calibration curve used to calculate the molecular weight distribution in polystyrene (PS): 500 to 3,787,000 (Measuring melt flow rate) The melt flow rate of aliphatic polyester resins was measured according to JIS K7210-1:2014, under conditions of a test temperature of 190°C and a nominal load of 2.16 kg. (Measurement of biomass content) The biomass content of aliphatic polyester resins was measured in accordance with ASTM D6866-21.

[0059] As described above, talc (KHP-125B, manufactured by Hayashi Chemical Co., Ltd.) was added to the prepared aliphatic polyester resin as a foam nucleating agent, magnesium stearate (Grade 1 magnesium stearate, manufactured by Kanto Chemical Co., Ltd.) as a foaming aid, and a hindered phenol antioxidant (Irganox 1010, manufactured by BASF Japan Ltd.) was added as an antioxidant. The mixture was melt-kneaded in a φ20 mm twin-screw extruder, extruded into strands, and cut to obtain resin particles with a diameter of 0.7 mm, a length of 3.5 mm, and an average weight of 2 mg. The talc, magnesium stearate, and antioxidant were added in masterbatches, with the amounts added being 0.1% by weight of talc, 0.5% by weight of magnesium stearate, and 0.01% by weight of the antioxidant per 100% by weight of the resin particles. Next, 500g of the above resin particles, 3500ml of water as a dispersion medium, 6.5g of aluminum oxide as a dispersant, 0.36g of sodium dodecylbenzenesulfonate as a dispersion aid, and 0.11 parts by weight of benzoyl peroxide (75% by weight of active ingredient in NOF Corporation's Niper BW) per 100 parts by weight of the resin particles were placed in a 5-liter autoclave at a temperature of 40°C or below, and nitrogen gas was introduced for 5 minutes to remove oxygen from inside the autoclave. Then, the contents of the autoclave were stirred and the temperature was raised to 75°C and held at that temperature for 30 minutes. Subsequently, the temperature was raised to 105°C, carbon dioxide gas was injected until the internal pressure of the autoclave reached 4.0 MPa, and the temperature was held at that temperature for 45 minutes. Subsequently, the contents were cooled to a temperature of 95°C, and carbon dioxide gas was injected into the autoclave until the internal pressure reached 4.0 MPa. This temperature was maintained for 5 minutes, and then one end of the autoclave was opened to introduce nitrogen gas, allowing the contents to be released to atmospheric pressure while maintaining the internal pressure, thereby obtaining foamed particles.

[0060] As described above, the bulk density, gel fraction, and degree of swelling of the obtained foamed particles were measured using the following method, and the degree of swelling / gel fraction and crosslinking efficiency were calculated from these values ​​and are shown in Table 1. (Bulk density of foamed particles) The foamed particles to be measured were left to cure for more than 24 hours in an environment of 23°C, 50% relative humidity, and 1 atm. The cured foamed particle group (weight W; 30g) was filled into a graduated cylinder, and the filling height of the foamed particle group in the graduated cylinder was stabilized by lightly tapping the floor surface several times with the bottom of the graduated cylinder. The bulk volume V (L) of the foamed particle group indicated by the scale on the graduated cylinder was read. Then, the weight W of the foamed particle group was divided by the bulk volume V (W / V). The value obtained from this was calculated in kg / m 3 By converting the units, the bulk density of the foamed particles (kg / m³) can be calculated. 3 ) was calculated. (Gel fraction of foamed particles) The gel fraction of the foamed particles was measured by the following gel filtration and drying processes. First, for the gel filtration process, approximately 0.25 g of the measured foamed particles (weight A) and 100 ml of cyclohexanone were placed in a 200 ml round-bottom flask. Under atmospheric pressure, the flask was heated with a heater to the boiling point of cyclohexanone (156°C) for 8 hours under reflux to extract the cyclohexanone-soluble components from the foamed particles and obtain a heat-treated product containing the cyclohexanone-insoluble components. An 80-mesh screen, whose weight had been measured in advance, was placed in a funnel, and the heat-treated product obtained as described above was filtered. The filtration process was performed for 1 minute, and it was confirmed that no droplets remained in the heat-treated product. Next, as a drying process, the heat-treated material collected on the mesh after the gel filtration process was dried in a fume hood at room temperature for 12 hours, and then dried in a vacuum oven at 80°C for 3 hours to obtain a dried product. After vacuum drying, the dried product was left at room temperature for 30 minutes, and its weight was measured (weight B). Using the weights measured as described above, the gel fraction of the gel contained in the foamed particles was calculated using the following formula (1). [Math 4] Gel fraction (weight %) = [weight B / weight A] × 100 ... (1) (Degree of swelling of the gel component in the foaming particles) The degree of swelling of the gel component contained in the foamed particles was measured as follows. The same procedure as the gel filtration treatment used in the measurement of the gel fraction described above was performed, and the resulting heat-treated material, still on the mesh, was placed on an aluminum dish whose weight had been measured in advance. The weight of the heat-treated material (weight C) was measured by subtracting the weight of the mesh and the aluminum dish. Then, using the weight B obtained in the drying treatment used in the measurement of the gel fraction described above, the degree of swelling of the gel component contained in the foamed particles was calculated using the following formula (2). [Number 5] Swelling degree (weight %) = [weight C / weight B] × 100 ... (2) As described above, the ratio of the degree of swelling to the gel fraction (degree of swelling / gel fraction) was calculated from the obtained degree of swelling and gel fraction. Furthermore, the measured gel fraction was divided by the amount (parts by weight) of the crosslinking agent used, and this value was defined as the crosslinking efficiency.

[0061] <Foam particle molded product> As described above, the obtained foamed particles were filled into a sealed container, pressurized with air to achieve the internal pressure shown in Table 1, then filled into a 65mm × 200mm × 40mm mold, and molded by heating with steam. The resulting foamed particle molded body was cured at 60°C under atmospheric pressure for 12 hours, and then left to stand at room temperature and pressure for 12 hours to obtain a foamed particle molded body. Furthermore, regarding the pressure inside the mold during foam particle molding, the lower and upper molding pressure limits described later were confirmed, and the moldable range was determined from these results.

[0062] (Lower molding pressure, upper molding pressure, and moldable range) Except for changing the mold pressure in 0.01 MPa (G) increments, the molding method described above was followed, and in-mold molding was performed to produce foamed particle molded bodies. The lowest molding pressure at which a molded body that passed all evaluations of secondary foaming properties, fusion properties, and recovery properties was obtained was defined as the lower limit molding pressure, and the highest molding pressure was defined as the upper limit molding pressure. The difference between the lower limit molding pressure and the upper limit molding pressure was calculated and defined as the moldable range.

[0063] Secondary foaming: A 50mm x 50mm rectangle was drawn in the center of the foam particle molded body, and then a diagonal line was drawn from one of the corners of this rectangle. The number of voids (gaps between foam particles) that were formed along this diagonal line and were larger than a 1mm square was counted, and a number of five or fewer voids was considered acceptable. Fusion properties: A foamed particle molded body (65 mm long x 200 mm wide x 40 mm thick) was folded and fractured so that it was divided into approximately equal parts along its length. The exposed fracture surface was visually observed, and the number of non-destructive foamed particles (n) present on the fracture surface (the number of foamed particles that were separated from each other at the interface between the fracture surfaces) and the number of foamed particles that were destroyed (b) were counted. The ratio of the number of foamed particles destroyed (b) to the total number of foamed particles destroyed (n) was then calculated. This ratio, expressed as a percentage (%), was defined as the bonding rate, and a bonding rate of 80% or higher was considered acceptable. Resilience: The presence or absence of a sink mark (so-called "depression") in the center of a 65mm long and 200mm wide foam particle molded body compared to its surroundings was evaluated. Specifically, the thickness of the central part of the surface defined by the vertical and horizontal edges of the obtained foam particle molded body, as well as the thickness of the four corners of that surface, were measured, and the ratio of the thickness of the central part to the thickness of the thickest part of the four corners was calculated. A thickness ratio of 99% or higher was considered acceptable.

[0064] As described above, the density of the molded foam particle molded body is (kg / m³ 3 The following measurements were taken. The measurement results are shown in Table 1. (Molded object density) The foam particle molded body was manufactured in the same manner as described above, except that the lower limit molding pressure shown in Table 1 was adopted. The density of the foam particle molded body obtained in this manner was calculated by dividing the weight of the foam particle molded body by the volume calculated based on the outer diameter.

[0065] <Examples 2-11, Comparative Examples 1-4> Except for the changes shown in Tables 1 and 2, foamed particles were manufactured in the same manner as in Example 1, and these were designated as Examples 2 to 11 and Comparative Examples 1 to 4, respectively. In addition, methyl methacrylate (MMA) was used as the crosslinking agent in Example 8 and Comparative Example 4, while divinylbenzene (DVB) was used as the crosslinking agent in Comparative Examples 1 and 2. The crosslinking agent was added in the masterbatch along with talc, magnesium stearate, and an antioxidant. In Example 9, Langshun's TH803S polybutylene succinate resin with a biomass content of 0% was used. In Example 10, carbon black was used as the coloring agent. The coloring agent was added in the masterbatch along with talc, magnesium stearate, and an antioxidant. Comparative Examples 1 and 2 used Bionole® #1001, manufactured by Showa Polymer Co., Ltd., with a biomass content of 0%, as the polybutylene succinate resin.

[0066] For the foamed particles obtained in Examples 2-11 and Comparative Examples 1-4 as described above, bulk density, gel fraction, degree of swelling, degree of swelling / gel fraction, and crosslinking efficiency were determined in the same manner as in Example 1. The obtained values ​​are shown in Tables 1-2. Except for using the foamed particles of Examples 2-11 and Comparative Examples 1-4, foamed particle molded articles were manufactured in the same manner as described above for the manufacturing method of foamed particle molded articles, and the lower limit molding pressure, upper limit molding pressure, moldable range, and molded article density were determined using the method described above. The obtained values ​​are shown in Tables 1-2.

[0067] <Examples 12-20> Except for changing the composition and additive amounts shown in Table 3, using polytetrafluoroethylene (PTFE) (TFW1000, manufactured by Seishin Corporation) instead of talc as a foam nucleating agent, using magnesium stearate (Grade 1 magnesium stearate, manufactured by Kanto Chemical Co., Ltd.) as a foaming aid, and performing a two-stage foaming process, foamed particles and molded foamed particle articles were produced in the same manner as in Example 1 (Examples 12-20). In Example 20, Langshun's TH803S, with a biomass content of 0%, was used as the polybutylene succinate resin. Furthermore, in the two-stage foaming process, foamed particles obtained by the same method as in Example 1 were used as the first-stage foamed particles. These first-stage foamed particles were supplied to a pressure vessel, and air was injected into the vessel as a foaming agent to pressurize them, increasing the internal pressure of the first-stage foamed particles to approximately 0.5 MPa. Subsequently, foaming was performed by heating with steam to obtain two-stage foamed particles. Except for using these two-stage foamed particles, the foamed particle molded body was manufactured in the same manner as in Example 1.

[0068] [Table 1]

[0069] [Table 2]

[0070] [Table 3]

[0071] The above embodiment encompasses the following technical concepts. (1) Aliphatic polyester resin foam particles using an aliphatic polyester resin as the base resin There is, Aliphatic polyester resin foamed particles characterized in that the foamed particles contain 5% to 70% by weight of gel, and the degree of swelling when the gel is swollen with cyclohexanone is 3500% to 6000% by weight. (2) The aliphatic polyester resin foam particle according to (1) above, characterized in that the ratio of the degree of swelling (weight%) to the gel content (weight%) is 70 or more and 500 or less. (3) The aliphatic polyester resin contains a 1,4-butanediol component and succinic acid and / or The aliphatic polyester resin foam particles according to (1) or (2) above, characterized in that they are copolymers having an adipic acid component. (4) The aliphatic polyester resin foam particles according to any one of (1) to (3) above, characterized in that the foam particles contain 10% by weight or more and 40% by weight or less of the gel component. (5) The bulk density of the foamed particles is 25 kg / m³ 3 More than 60kg / m 3 Aliphatic polyester resin foamed particles according to any one of the above (1) to (4), characterized in that: (6) A method for producing aliphatic polyester resin foamed particles, wherein resin particles obtained by kneading an aliphatic polyester resin are crosslinked with an organic peroxide in an aqueous medium in a sealed container, and the resin particles are foamed to obtain foamed particles, The weight-average molecular weight Mw of the aliphatic polyester resin is 100,000 or more and 190,000 or less. The ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the aliphatic polyester resin, Mw / Mn, is 5 or more and 15 or less. A method for producing aliphatic polyester resin foam particles, characterized in that the foam particles contain 5% by weight or more and 70% by weight or less of gel content. (7) A method for producing aliphatic polyester resin foam particles according to (6) above, characterized in that the degree of swelling when the gel component is swollen with cyclohexanone is 3500% by weight or more and 6000% by weight or less. (8) A method for producing aliphatic polyester resin foam particles according to (6) or (7) above, characterized in that the melt flow rate of the aliphatic polyester resin at a temperature of 190°C and a nominal load of 2.16 kg is 4 g / 10 min or more and 20 g / 10 min or less. (9) A method for producing aliphatic polyester resin foam particles according to any one of (6) to (8) above, characterized in that the biomass content of the aliphatic polyester resin is 10% by weight or more. (10) A method for producing aliphatic polyester resin foam particles according to any one of (6) to (9) above, characterized in that the resin particles are resin particles obtained by kneading an aliphatic polyester resin and a phenolic antioxidant, and the amount of the phenolic antioxidant added is 0.0005% by weight or more and 0.08% by weight or less per 100% by weight of the resin particles. (11) The bulk density of the foamed particles is 25 kg / m³ 3 More than 60kg / m 3 A method for producing aliphatic polyester resin foam particles according to any one of the above items (6) to (10), characterized in that it is as follows:

Claims

1. Aliphatic polyester resin foam particles using an aliphatic polyester resin as the base resin, Aliphatic polyester resin foam particles characterized in that the foam particles contain 5% to 70% by weight of gel, and the degree of swelling when the gel is swollen with cyclohexanone is 3500% to 6000% by weight.

2. The aliphatic polyester resin foam particle according to claim 1, characterized in that the ratio of the degree of swelling (weight%) to the gel content (weight%) is 70 or more and 500 or less.

3. The aliphatic polyester resin comprises a 1,4-butanediol component and succinic acid and / or The aliphatic polyester resin foam particles according to claim 1 or 2, characterized in that they are a polymer having a dipic acid component.

4. The aliphatic polyester resin foamed particle according to claim 1 or 2, characterized in that the foamed particle contains 10% by weight or more and 40% by weight or less of the gel component.

5. The bulk density of the foamed particles is 25 kg / m³ ３ More than 60kg / m ３ The aliphatic polyester resin foam particles according to claim 1 or 2, characterized in that they are as follows:

6. A method for producing foamed aliphatic polyester resin particles, comprising kneading an aliphatic polyester resin to obtain resin particles, crosslinking the resin particles with an organic peroxide in an aqueous medium in a sealed container, and foaming the resin particles to obtain foamed particles, The weight-average molecular weight Mw of the aliphatic polyester resin is 100,000 or more and 190,000 or less. The ratio of the weight-average molecular weight Mw to the number-average molecular weight Mn of the aliphatic polyester resin, Mw / Mn, is 5 or more and 15 or less. The foamed particles contain 5% by weight or more and 70% by weight or less of gel. A method for producing aliphatic polyester resin foam particles, characterized in that the degree of swelling when the gel component is swollen with cyclohexanone is 3500% by weight or more and 6000% by weight or less.

7. A method for producing aliphatic polyester resin foam particles according to claim 6, characterized in that the melt flow rate of the aliphatic polyester resin at a temperature of 190°C and a nominal load of 2.16 kg is 4 g / 10 min or more and 20 g / 10 min or less.

8. A method for producing aliphatic polyester resin foam particles according to claim 6 or 7, characterized in that the biomass content of the aliphatic polyester resin is 10% by weight or more.

9. The method for producing aliphatic polyester resin foam particles according to claim 6 or 7, characterized in that the resin particles are resin particles obtained by kneading an aliphatic polyester resin and a phenolic antioxidant, and the amount of the phenolic antioxidant added is 0.0005% by weight or more and 0.08% by weight or less per 100% by weight of the resin particles.

10. The bulk density of the foamed particles is 25 kg / m³ ３ More than 60kg / m ３ A method for producing aliphatic polyester resin foam particles according to claim 6 or 7, characterized in that it is as follows:

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