Method for producing foamable particles

Abstract

To provide a method for producing foamable particles that can suppress generation of wrinkles and flattening of resin foam particles, and to provide a method for producing foamable particles.SOLUTION: A method for producing foamable particles includes a resin particle production step of heating styrene-based resin particles to form a resin melt, extruding the resin melt to form a strand, and then cutting the strand to obtain resin particles, and a blowing-agent impregnation step of obtaining foamable particles by impregnating a blowing agent into the resin particles dispersed in an aqueous medium. A melt mass flow rate of the resin particles is 0.5 to 20 g / 10 min. An addition amount of the blowing agent is 8 to 16 pts.mass with respect to 100 pts.mass of the resin particles. The blowing agent contains a saturated hydrocarbon having 4 carbon atoms and a saturated hydrocarbon having 5 carbon atoms at a specific ratio.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a method for producing expandable granules. [Background technology]

[0002] A known method for producing expandable particles is to heat a styrene-based resin to form a resin melt, extrude the resin melt to form strands, cut the strands to form resin particles, and impregnate the resin particles with a blowing agent.

[0003] However, when resin beads are prepared by cutting strands made from a styrene-based resin and then the resin beads are softened by heating during impregnation of the resin beads with a blowing agent, the expandable beads may be deformed into a flat shape. When such flat expandable beads are expanded, the shape of the resulting resin expanded beads also becomes flat, which may lead to deterioration in the fillability into a molding die and the appearance of the styrene-based resin expanded bead molding obtained after in-mold molding.

[0004] To address this problem, techniques for suppressing deformation of resin particles during impregnation with a blowing agent have been investigated. For example, Patent Document 1 describes a method for producing recycled expandable styrene-based resin particles, which comprises pelletizing an expandable styrene-based resin having a resin fluidity (melt flow index) in the range of 5 to 15 g / 10 min at a heating temperature of 220 to 260°C in an extruder, and then impregnating the pellets with a blowing agent. Patent Document 1 also uses butane as the blowing agent. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-309659 Summary of the Invention [Problem to be solved by the invention]

[0006] However, when the expandable beads obtained by the manufacturing method described in Patent Document 1 are expanded, wrinkles sometimes occur on the surface of the resin foam beads obtained after expansion. On the other hand, when attempting to obtain resin foam beads with reduced wrinkles, the shape of the resin foam beads sometimes becomes flattened, making it difficult to obtain good resin foam beads. Furthermore, when such wrinkled resin foam beads are used for in-mold molding, there is a risk that the appearance of the molded product obtained after in-mold molding will deteriorate.

[0007] The present invention has been made in view of the above background, and aims to provide a method for producing expandable resin beads that can suppress the occurrence of wrinkles and flattening of the expanded resin beads. [Means for solving the problem]

[0008] One aspect of the present invention is a method for producing expandable granules according to the following items [1] to [6].

[0009] [1] a resin particle production step of heating a styrene-based resin to form a resin melt, extruding the resin melt to form strands, and then cutting the strands to obtain resin particles; a blowing agent impregnation step of impregnating the resin particles dispersed in the aqueous medium with a blowing agent to obtain expandable particles, the resin particles have a melt mass flow rate of 0.5 g / 10 min or more and 20 g / 10 min or less, as measured under conditions of a temperature of 200°C and a load of 5 kg; the amount of the foaming agent added is 8 parts by mass or more and 16 parts by mass or less with respect to 100 parts by mass of the resin particles, the blowing agent comprises a saturated hydrocarbon having 4 carbon atoms and a saturated hydrocarbon having 5 carbon atoms, A method for producing expandable particles, wherein the mass ratio of the saturated hydrocarbon having 4 carbon atoms to the saturated hydrocarbon having 5 carbon atoms in the blowing agent is 20:80 to 90:10.

[0010] [2] The method for producing expandable particles according to [1], wherein the mass ratio of the saturated hydrocarbon having 4 carbon atoms to the saturated hydrocarbon having 5 carbon atoms in the foaming agent is 60:40 to 90:10. [3] The method for producing expandable granules according to [1] or [2], wherein the styrene-based resin includes a styrene-based resin derived from a recycled styrene-based resin material. [4] The method for producing expandable granules according to any one of [1] to [3], wherein the resin granules have a cylindrical shape and the ratio (L / D) of the length L to the outer diameter D of the resin granules is 1.5 or more and 4.0 or less.

[0011] [5] The method for producing expandable particles according to any one of [1] to [4], wherein in the resin particle production step, a styrene-based resin and talc and / or ethylene bisstearic acid amide are heated to form a resin melt, the resin melt is extruded to form strands, and then the strands are cut to obtain resin particles. [6] The method for producing expandable granules according to any one of [1] to [5], wherein in the blowing agent impregnation step, the temperature of the aqueous medium when the blowing agent is impregnated into the resin granules is 105°C or higher and 125°C or lower. [Effects of the Invention]

[0012] According to the above-described embodiment, it is possible to provide a method for producing expandable beads that can suppress the occurrence of wrinkles and flattening of the expanded resin beads. [Brief explanation of the drawings]

[0013] [Figure 1] FIG. 1 is an enlarged photograph showing the appearance of expanded resin beads having a diameter of 5 mm produced using the expandable beads of Example 1. [Figure 2] FIG. 2 is an enlarged photograph showing the appearance of expanded resin beads having a diameter of 5 mm produced using the expandable beads of Comparative Example 2. DETAILED DESCRIPTION OF THE INVENTION

[0014] (Method for producing expandable granules) Each step in the manufacturing method will now be described in detail.

[0015] [Resin particle manufacturing process] In the resin particle manufacturing process, a styrene-based resin is heated to form a resin melt, the resin melt is extruded to form strands composed of the styrene-based resin, and then the strands are cut to produce resin particles composed of the styrene-based resin.

[0016] In the resin particle production process, a styrene-based resin introduced into an extruder is heated and melted in the extruder to produce a resin melt. The resin melt then passes through the discharge holes of a die lip installed at the resin outlet of the extruder, forming strands with a cross-sectional shape corresponding to the shape of the discharge holes. From the viewpoint of further reducing flattening of the expandable particles obtained in subsequent processes and avoiding excessive increases in the melt mass-flow rate of the resin particles, the heating temperature in the extruder is preferably in the range of 190°C to 250°C, more preferably 200°C to 248°C, even more preferably 210°C to 245°C, and particularly preferably 220°C to 243°C. The heating temperature can be adjusted, for example, by changing the cylinder temperature of the extruder.

[0017] As the styrene-based resin, a styrene homopolymer or a styrene copolymer containing 50% by mass or more of structural units derived from styrene can be used. Examples of the styrene homopolymer include general-purpose polystyrene (GPPS). Examples of the styrene copolymer include a styrene-acrylic acid copolymer, a styrene-methyl acrylate copolymer, a styrene-ethyl acrylate copolymer, a styrene-butyl acrylate copolymer, a styrene-methacrylic acid copolymer, a styrene-methyl methacrylate copolymer, a styrene-ethyl methacrylate copolymer, a styrene-butyl methacrylate copolymer, a styrene-maleic anhydride copolymer, a styrene-acrylonitrile copolymer, an acrylonitrile-butadiene-styrene copolymer, a styrene-methylstyrene copolymer, a styrene-dimethylstyrene copolymer, a styrene-ethylstyrene copolymer, and a styrene-diethylstyrene copolymer. For the production of resin particles, one styrene-based resin selected from the group consisting of these styrene-based resins may be used, or two or more styrene-based resins may be used.

[0018] The proportion of styrene homopolymer and styrene copolymer in the styrene resin is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 97% by mass or more, and particularly preferably 99% by mass or more. The styrene resin may contain a resin or elastomer other than the styrene resin to the extent that the above-mentioned effects are not impaired.

[0019] Examples of polymer components other than the styrene-based resin that can be contained in the styrene-based resin include resins and elastomers such as low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, polyester, polyamide, polycarbonate, acrylic resin, etc. From the viewpoint of making it easier to obtain spherical expanded resin beads, the proportion of resins and elastomers other than the styrene-based resin in the styrene-based resin is preferably 10% by mass or less, more preferably 5% by mass or less, even more preferably 3% by mass or less, and particularly preferably 1% by mass or less.

[0020] From the viewpoints of suppressing an increase in residual stress in the strands and resin particles and suppressing flattening of the expandable particles and resin foam particles, the melt mass-flow rate of the styrene-based resin is preferably 0.5 g / 10 min or more, more preferably 1.5 g / 10 min or more, even more preferably 3 g / 10 min or more, and particularly preferably 4 g / 10 min or more. On the other hand, from the viewpoint of easily producing strands using the styrene-based resin, the melt mass-flow rate of the styrene-based resin is preferably 20 g / 10 min or less, more preferably 18 g / 10 min or less, even more preferably 15 g / 10 min or less, and particularly preferably 12 g / 10 min or less.

[0021] The melt mass-flow rate of the styrene-based resin described above is a value measured at a temperature of 200°C and a load of 5 kg in accordance with JIS K7210-1:2014. Furthermore, when determining a preferred range of the melt mass-flow rate of the styrene-based resin, the upper and lower limits of the melt mass-flow rate described above can be combined arbitrarily. The preferred range of the melt mass-flow rate of the styrene-based resin may be, for example, 1.5 g / 10 min or more and 18 g / 10 min or less, 3 g / 10 min or more and 15 g / 10 min or less, or 4 g / 10 min or more and 12 g / 10 min or less.

[0022] The styrene resin used in the production of resin particles may be a non-recycled styrene resin or a styrene resin derived from a recycled styrene resin material. In this specification, the styrene resin derived from a recycled styrene resin material includes, for example, a styrene resin derived from recovered materials such as post-consumer materials, scraps generated during the production of plastic products, non-standard products, and offcuts.

[0023] Styrenic resins derived from recycled styrene-based resin materials have various molecular weights and compositions depending on the intended use before recovery. As mentioned above, styrene-based resins derived from recycled styrene-based resin materials are prone to large variations in resin properties between production lots and within the same production lot, more specifically, large variations in resin properties during melting. Therefore, when resin particles are produced using styrene-based resins derived from recycled styrene-based resin materials, even under constant production conditions, variations in resin properties tend to cause variations in the magnitude of residual stress among resin particles. In such cases, shape variation is particularly large, and the shape of expandable particles and resin foam particles is more likely to become flattened.

[0024] In contrast, in the above-mentioned manufacturing method, by carrying out the resin particle manufacturing process and the blowing agent impregnation process in the manner described above, the effect of variations in residual stress in the resin particles can be reduced, and even when expandable particles are manufactured using styrene-based resin derived from recycled styrene-based resin material, flattening of the expandable particles can be suppressed, making it easier to obtain expandable particles having a spherical shape.

[0025] Therefore, by producing expandable particles using a styrene-based resin derived from a recycled styrene-based resin material, the recycled styrene-based resin material can be effectively utilized as a resource. Also, from the viewpoint of reducing the amount of waste, it is preferable that the styrene-based resin used in producing the resin particles contains a styrene-based resin derived from a recycled styrene-based resin material.

[0026] Recycled styrene-based resin materials are derived from styrene-based products containing styrene-based resin as a primary component. More specifically, examples of such styrene-based products include refrigerator shelves, recording media such as CDs, packaging materials, cushioning materials, food trays, lost patterns for casting, chemical laboratory equipment, expandable granules, resin foam granules, and resin foam granule molded articles. The recycled styrene-based resin materials may be post-consumer materials or pre-consumer materials such as scrap, non-standard products, and offcuts generated during the production of styrene-based products. Using these recycled styrene-based resin materials as raw materials for the expandable granules allows for the recycling of various recycled styrene-based resin materials as resources. The proportion of styrene-based resin in the recycled styrene-based resin material is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 97% by mass or more.

[0027] The recycled styrene-based resin material may be the above-mentioned styrene-based article itself. Alternatively, the recycled styrene-based resin material may be an ingot, flake, pellet, or the like obtained by subjecting the styrene-based article to processing such as compression, melting, crushing, or granulation. From the viewpoint of handling of the raw material during production, the recycled styrene-based resin material is preferably in the form of flakes, pellets, or the like.

[0028] When the styrene-based resin is heated to form a resin melt, additives such as a cell regulator, an antistatic agent, an antioxidant, an ultraviolet absorber, a light stabilizer, a colorant, and a lubricant may be added as needed. Examples of the cell regulator that can be used include methyl methacrylate copolymers, polyethylene wax, talc, silica, ethylene bis(stearic acid amide), and silicone. It is preferable to use at least one of talc and ethylene bis(stearic acid amide), and it is more preferable to use both talc and ethylene bis(stearic acid amide). In this case, expandable particles capable of forming expanded resin beads having a good cell structure can be easily obtained. Furthermore, the expanded styrene-based resin bead molded article (hereinafter referred to as the "molded article") obtained by molding the expanded resin beads having a good cell structure also has excellent mechanical properties such as bending strength and compressive modulus.

[0029] Examples of the antistatic agent that can be used include alkyldiethanolamine, glycerin fatty acid ester, and sodium alkylsulfonate. Examples of the antioxidant that can be used include phenol-based antioxidants, phosphorus-based antioxidants, and sulfur-based antioxidants. Examples of the ultraviolet absorber that can be used include benzotriazole-based ultraviolet absorbers and benzophenone-based ultraviolet absorbers. Examples of the light stabilizer that can be used include hindered amine-based light stabilizers.

[0030] When a styrene-based resin is heated to form a resin melt, a resin other than the styrene-based resin or an elastomer may be added to the styrene-based resin to the extent that the above-mentioned effects are not impaired. Examples of resins other than the styrene-based resin that can be added to the styrene-based resin include low-density polyethylene, linear low-density polyethylene, high-density polyethylene, polypropylene, polyester, polyamide, polycarbonate, and acrylic resin. From the viewpoint of making it easier to obtain spherical expanded resin beads, the proportion of resins other than the styrene-based resin and elastomers in the resin melt is preferably 10% by mass or less, more preferably 5% by mass or less, and even more preferably 1% by mass or less.

[0031] In the resin particle production process, after the resin melt is extruded, the strand may be cooled to stabilize the strand shape. The method for cooling the strand is not particularly limited, and various modes may be used. For example, the strand may be cooled in water by passing it through a water tank. When cooling the strand in water, the water temperature is preferably 5°C or higher and 50°C or lower, and more preferably 7°C or higher and 40°C or lower.

[0032] When forming strands by extruding the resin melt, the strands may be taken up in order to stably produce resin particles. The method for taking up the strands is not particularly limited and various modes are possible. For example, the strands may be taken up at a constant speed using a roll whose rotation speed is adjustable. The take-up speed when taking up the strands can be adjusted, for example, by the rotation speed of the roll during take-up. The take-up speed may be set appropriately depending on the desired size and mass of the resin particles. Specific methods for adjusting the size and mass of the resin particles will be described later. From the viewpoint of stably forming strands and stably producing resin particles, the take-up speed is preferably in the range of 1 m / min to 100 m / min.

[0033] The resin particles are produced by cutting the strands. The method for cutting the strands is not particularly limited and may take various forms. For example, the strands can be cut using a known device such as a strand cutter that can adjust the cutting interval of the strands.

[0034] The melt mass-flow rate of the resin particles is 0.5 g / 10 min or more. If the melt mass-flow rate of the resin particles is too low, the fluidity of the resin melt extruded in the resin particle production process will be low, and the strands after extrusion from the extruder will be more likely to be stretched strongly. This may increase the residual stress in the strands and resin particles, making it difficult to suppress flattening of the expandable particles and resin foam particles. Furthermore, if the residual stress in the resin particles is large, the resin particles will be more likely to deform into a flat shape when impregnated with a blowing agent.

[0035] By setting the melt mass-flow rate of the resin particles to 0.5 g / 10 min or more, these problems can be easily avoided and flattening of the expandable particles and resin foam particles can be easily suppressed. From the same viewpoint, the melt mass-flow rate of the resin particles is preferably 1.5 g / 10 min or more, more preferably 3 g / 10 min or more, and even more preferably 4 g / 10 min or more.

[0036] The resin particles have a melt mass-flow rate of 20 g / 10 min or less. If the resin particles have a melt mass-flow rate that is too high, the fluidity of the resin melt becomes excessively high, making it difficult to stably produce strands. To easily avoid such problems, the resin particles have a melt mass-flow rate of 20 g / 10 min or less. To more easily extrude the resin melt to form strands, the styrene resin preferably has a melt mass-flow rate of 18 g / 10 min or less, more preferably 15 g / 10 min or less, and even more preferably 12 g / 10 min or less.

[0037] The resin particles obtained in the resin particle production process may have, for example, a cylindrical shape. In this case, the ratio of the length L to the outer diameter D of the resin particles (L / D) is preferably 1.5 or more and 4.0 or less. By setting the L / D ratio of the resin particles within the above-mentioned specific range, flattening of the expandable particles and resin foam particles can be more easily suppressed.

[0038] The outer diameter D of the resin particle mentioned above refers to the diameter of a circle circumscribing the outline of the resin particle in a cross section perpendicular to the axial direction of the resin particle. For example, if the outline of the resin particle in a cross section perpendicular to the axial direction of the resin particle is a perfect circle, the outer diameter D of the resin particle is equal to the diameter of the perfect circle. Furthermore, for example, if the outline of the resin particle in a cross section perpendicular to the axial direction of the resin particle is an ellipse, the outer diameter D of the resin particle is equal to the major axis of the ellipse.

[0039] The outer diameter D of the resin particles is not particularly limited, but can be set appropriately within the range of, for example, 0.1 mm to 2 mm. The length L of the resin particles is not particularly limited, but can be set appropriately within the range of, for example, 0.3 mm to 8 mm.

[0040] The mass of each resin particle is preferably 0.1 mg to 5 mg. By setting the mass of each resin particle within the above-mentioned specific range, the fillability of the expanded resin beads obtained from the expandable beads can be further improved when they are molded in a mold.

[0041] The L / D and mass of the resin particles obtained in the resin particle production process can be adjusted based on the extrusion rate per unit time of the extruder, the strand take-up speed, and the strand cutting interval. Specifically, if only the extrusion rate per unit time from the extruder is increased among the three conditions mentioned above, the outer diameter D of the resin particles increases and the L / D of the resin particles decreases. Conversely, if only the extrusion rate is decreased, the outer diameter D of the resin particles decreases and the L / D of the resin particles increases. Conversely, if only the take-up speed of the extrudate is increased among the three conditions mentioned above, the outer diameter D of the resin particles decreases and the L / D of the resin particles increases. Conversely, if only the take-up speed is decreased, the outer diameter D of the resin particles increases and the L / D of the resin particles decreases. Conversely, if only the take-up speed is decreased, the outer diameter D of the resin particles increases and the L / D of the resin particles decreases. If only the strand cutting interval is increased among the three conditions mentioned above, the length L of the resin particles increases and the L / D and mass of the resin particles increase. On the other hand, if the cutting interval is shortened, the length L of the resin particles will be shortened, and the L / D and mass of the resin particles will be reduced. Therefore, by adjusting the above-mentioned conditions, resin particles having the desired dimensions and mass can be easily obtained.

[0042] When a styrene-based resin melt is extruded in the resin particle manufacturing process, the strands are stretched, and a force (stress) that resists the stretching is applied to the stretched strands. This stress is not completely released between the time the resin melt is extruded and the time the strand shape stabilizes, resulting in residual stress in the strands. Therefore, resin particles obtained by cutting strands with residual stress also have residual stress. Resin particles with residual stress shrink in the longitudinal direction of the resin particles when softened by heating due to the residual stress.

[0043] The magnitude of the residual stress of the resin particles can be estimated based on the Lt / Dt change rate (unit: %) calculated using the L / D value LD1 of the resin particles and the Lt / Dt value LD2 of the ratio Lt to the outer diameter Dt of the resin particles after heat treatment without adding a foaming agent, using the Lt / Dt value LD2 using the Lt / Dt value LD1 of the resin particles. Lt / Dt change rate = {(LD2 - LD1) / LD1} × 100 (1)

[0044] The Lt / Dt change rate of resin particles after heat treatment is measured as follows. First, an aqueous medium, resin particles, dispersant, and surfactant are placed in a sealed container equipped with a stirring blade. Heat treatment and stirring are performed at a temperature at which the resin particles soften without adding a blowing agent. The sealed container is then cooled to a temperature below the softening point of the resin particles, and the heat-treated resin particles are removed. The length Lt and outer diameter Dt of the resin particles after heat treatment are measured using the same method as for the resin particles before heat treatment, and the Lt / Dt of the resin particles after heat treatment is calculated based on these values. The measurement direction of the length Lt and outer diameter Dt of the resin particles after heat treatment can be determined based on the shape of the resin particles observed visually.

[0045] Using the Lt / Dt value LD2 of the resin particles after heat treatment and the L / D value LD1 of the resin particles before heat treatment obtained above, the Lt / Dt change rate (unit: %) of the resin particles after heat treatment can be calculated based on the above formula (1). From the viewpoint of increasing the extruder output per hour and further improving the manufacturability of resin particles, the Lt / Dt change rate of the resin particles after heat treatment is preferably -30% or less, more preferably -40% or less, even more preferably -50% or less, and particularly preferably -60% or less. On the other hand, from the viewpoint of more easily suppressing flattening of expandable particles and expanded resin particles, the Lt / Dt change rate of the resin particles after heat treatment is preferably -90% or more, more preferably -80% or more, even more preferably -75% or more, and particularly preferably -70% or more.

[0046] [Foaming agent impregnation step] In the foaming agent impregnation step of the production method, for example, resin particles, a dispersant, and a surfactant are dispersed in an aqueous medium, and the dispersion is heated with stirring in the presence of a foaming agent to obtain expandable particles. In the foaming agent impregnation step, the timing of adding the foaming agent to the aqueous medium is not particularly limited. For example, the foaming agent may be added before or after dispersing the resin particles. The foaming agent may also be added before, during, or after heating the resin particles. From the viewpoint of making it easier to disperse the resin particles in the aqueous medium, it is preferable to add the foaming agent to the aqueous medium after the temperature of the resin particles reaches the impregnation temperature. From the viewpoint of more easily preventing flattening of the expandable particles and expanded resin particles, it is preferable to complete the addition of the foaming agent to the aqueous medium within 60 minutes from the time when the temperature of the resin particles reaches the impregnation temperature.

[0047] The amount of the blowing agent added in the blowing agent impregnation step is 8 parts by mass or more and 16 parts by mass or less per 100 parts by mass of the resin particles. The blowing agent contains saturated hydrocarbons with 4 carbon atoms and saturated hydrocarbons with 5 carbon atoms, and the mass ratio of the saturated hydrocarbons with 4 carbon atoms to the saturated hydrocarbons with 5 carbon atoms in the blowing agent is 20:80 to 90:10, where the total mass ratio of the saturated hydrocarbons with 4 carbon atoms to the saturated hydrocarbons with 5 carbon atoms is 100.

[0048] The blowing agent may contain one saturated hydrocarbon having 4 carbon atoms, or may contain two or more saturated hydrocarbons having 4 carbon atoms. The saturated hydrocarbon having 4 carbon atoms may be a chain saturated hydrocarbon or a cyclic saturated hydrocarbon. Examples of the chain saturated hydrocarbon having 4 carbon atoms include normal butane and isobutane. Examples of the cyclic saturated hydrocarbon having 4 carbon atoms include cyclobutane. The saturated hydrocarbon having 4 carbon atoms contained in the blowing agent is preferably composed of a chain saturated hydrocarbon having 4 carbon atoms, and more preferably composed of normal butane and isobutane. When the saturated hydrocarbon having 4 carbon atoms is composed of normal butane and isobutane, the proportion of normal butane relative to the total of normal butane and isobutane (100% by mass) is preferably 50% by mass or more, and more preferably 60% by mass or more.

[0049] The blowing agent may contain one type of saturated hydrocarbon having 5 carbon atoms, or may contain two or more types of saturated hydrocarbons having 5 carbon atoms. The saturated hydrocarbons having 5 carbon atoms may be chain saturated hydrocarbons or cyclic saturated hydrocarbons. Examples of chain saturated hydrocarbons having 5 carbon atoms include normal pentane, isopentane, and neopentane. Examples of cyclic saturated hydrocarbons having 5 carbon atoms include cyclopentane. The chain saturated hydrocarbons having 5 carbon atoms contained in the blowing agent are preferably composed of chain saturated hydrocarbons having 5 carbon atoms, and more preferably composed of normal pentane and isopentane. When the saturated hydrocarbons having 5 carbon atoms are composed of normal pentane and isopentane, the proportion of normal pentane relative to the total of normal pentane and isopentane (100% by mass) is preferably 50% by mass or more, more preferably 60% by mass or more, and even more preferably 70% by mass or more.

[0050] If the amount of foaming agent added in the foaming agent impregnation step is too small, the expandable particles may be easily deformed into a flat shape, making it difficult to prevent the resin foam particles from becoming flattened. By adding the foaming agent in an amount of 8 parts by mass or more, preferably 9 parts by mass or more, more preferably 10 parts by mass or more, and even more preferably 11 parts by mass or more per 100 parts by mass of the resin particles, it is possible to more easily prevent the expandable particles and resin foam particles from becoming flattened.

[0051] If the amount of foaming agent added is too large, wrinkles are likely to form on the surface of the resin foam beads when the expandable beads are expanded. Furthermore, when such resin foam beads are molded in a mold, wrinkles are likely to form on the surface of the molded product. By setting the amount of foaming agent added to 16 parts by mass or less, preferably 15.5 parts by mass or less, more preferably 15 parts by mass or less, and even more preferably 14.5 parts by mass or less per 100 parts by mass of resin beads, it is possible to easily avoid such problems and obtain expandable beads that can be used to form resin foam beads with good appearance and molded products.

[0052] The wrinkles on the surface of the resin foam beads mentioned above are visually observable irregularities that arise due to the diffusion of the blowing agent from the surface of the resin foam beads. As an example, Fig. 1 shows an enlarged photograph of a resin foam bead 1 with no wrinkles on its surface, and Fig. 2 shows an enlarged photograph of a resin foam bead 8 with wrinkles on its surface. The wrinkles mentioned above are distinct from shrinkage, which occurs when holes are created in the cell membrane during the production of resin foam beads from expandable beads, reducing the closed cell ratio and the overall volume of the resin foam beads.

[0053] If the mass ratio of saturated hydrocarbons having 4 carbon atoms in the blowing agent used in the blowing agent impregnation step is too low and the mass ratio of saturated hydrocarbons having 5 carbon atoms is too high, the cell diameter of the expanded resin beads tends to be large and the variation in cell diameter tends to be large. In this case, wrinkles are likely to occur on the surface of the expanded resin beads when the expandable beads are expanded. Furthermore, if the mass ratio of saturated hydrocarbons having 4 carbon atoms in the blowing agent used in the blowing agent impregnation step is too high and the mass ratio of saturated hydrocarbons having 5 carbon atoms is too low, wrinkles are likely to occur on the surface of the expanded resin beads when the expandable beads are expanded. Furthermore, when such expanded resin beads are molded in a mold, the surface appearance of the molded body after molded in a mold is likely to be deteriorated. By setting the mass ratio of the saturated hydrocarbon having 4 carbon atoms to the saturated hydrocarbon having 5 carbon atoms in the foaming agent within a range of preferably 20:80 to 90:10, more preferably 45:55 to 90:10, and even more preferably 60:40 to 90:10, it is possible to easily avoid such problems and obtain expandable resin beads with good appearance and expandable beads that can be used to form molded articles.

[0054] The reason why the combined use of a saturated hydrocarbon having four carbon atoms and a saturated hydrocarbon having five carbon atoms can suppress the occurrence of wrinkles on the surface of expanded resin beads is not entirely clear, but the following reasons are thought to be possible: Saturated hydrocarbons having four carbon atoms have a relatively low ability to plasticize styrene-based resins. On the other hand, saturated hydrocarbons having four carbon atoms have a boiling point in the range of -20°C to 10°C, making them prone to volatilization. Therefore, when only saturated hydrocarbons having four carbon atoms are used as the blowing agent, it is thought that the blowing agent tends to diffuse excessively from the surface of the expanded resin beads immediately after the expandable beads are expanded, causing a decrease in the internal pressure of the bubbles near the surface of the expanded resin beads. As a result, wrinkles are formed on the surface of the expanded resin beads, which is thought to lead to a deterioration in appearance.

[0055] Furthermore, when such expanded resin beads are molded in a mold, voids resulting from the gaps between the expanded resin beads are likely to form on the surface of the molded article after molding in a mold because the styrene-based resin is not plasticized sufficiently.Furthermore, it is thought that wrinkles are likely to occur on the surface of the molded article due to the large amount of blowing agent diffusing from the surface of the molded article immediately after molding.

[0056] In contrast, saturated hydrocarbons with 5 carbon atoms have a relatively high ability to plasticize styrene-based resins. On the other hand, the boiling points of saturated hydrocarbons with 5 carbon atoms are in the range of 20°C or higher and 60°C or lower, and they are less likely to volatilize. Therefore, when only saturated hydrocarbons with 5 carbon atoms are used as the blowing agent, it is thought that a relatively long time is required for the shape of the resin foam particles to stabilize after the expandable particles are expanded. Furthermore, it is thought that the blowing agent dissipates from the surface of the resin foam particles during the time until the shape of the resin foam particles stabilizes, causing wrinkles on the surface of the resin foam particles and deteriorating their appearance.

[0057] Furthermore, when such foamed resin beads are molded in a mold, it is thought that secondary expansion of the foamed resin beads is likely to be insufficient. As a result, it is thought that voids are likely to be formed on the surface of the molded article. Furthermore, it is thought that wrinkles are likely to occur on the surface of the molded article due to the diffusion of the foaming agent from the surface of the molded article during the period from immediately after molding until the shape of the molded article is stabilized.

[0058] In the above-mentioned production method, by using a saturated hydrocarbon having four carbon atoms and a saturated hydrocarbon having five carbon atoms, which have different properties, in the above-mentioned specific ratio, it is believed that the properties of the saturated hydrocarbons described above can be exhibited in a balanced manner, and the occurrence of wrinkles on the surface of the expanded resin beads and the surface of the molded article can be suppressed. Furthermore, by molding such expanded resin beads in a mold, it is believed that the styrene-based resin can be appropriately plasticized during molding in the mold and the expanded resin beads can be sufficiently secondary-expanded, thereby suppressing the occurrence of voids on the surface of the molded article.

[0059] Furthermore, the reason why flattening of the resin foam particles can be suppressed by using a blowing agent having a mass ratio within the above-mentioned specific range in the blowing agent impregnation step is not entirely clear, but the following reason is thought to be one example. Both saturated hydrocarbons with four carbon atoms and saturated hydrocarbons with five carbon atoms have the effect of plasticizing styrene-based resins. Therefore, by impregnating resin particles with a blowing agent containing a saturated hydrocarbon with four carbon atoms and a saturated hydrocarbon with five carbon atoms in the blowing agent impregnation step, at least a portion of the residual stress in the resin particles can be released. As a result, it is thought that flattening of the expandable particles and the resin foam particles can be suppressed by suppressing shrinkage of the resin particles in the longitudinal direction when the resin particles soften. In particular, in the present invention, by setting the blending ratio of the saturated hydrocarbon with four carbon atoms and the saturated hydrocarbon with five carbon atoms within the above-mentioned specific range, it becomes easier to produce expandable particles that can produce resin foam particles that are suppressed from flattening and have reduced wrinkles.

[0060] In the blowing agent impregnation step, by using a blowing agent in which the mass ratio of saturated hydrocarbons having four carbon atoms to saturated hydrocarbons having five carbon atoms is within the above-mentioned specific range and by adjusting the amount of the blowing agent added within the above-mentioned specific range, flattening of the expandable particles can be easily suppressed. Furthermore, by expanding the expandable particles containing the blowing agent, resin expanded particles capable of forming molded articles with good appearance can be easily obtained. In particular, in the present invention, by adjusting the amount of the blowing agent added in a specific ratio when producing the expandable particles, the influence of residual stresses experienced during the resin particle production process can be reduced. Therefore, by impregnating resin particles having a melt mass-flow rate within the above-mentioned specific range with the blowing agent, flattening of the expandable particles and the resin expanded particles can be suppressed.

[0061] The blowing agent used in the blowing agent impregnation step may be composed of saturated hydrocarbons having 4 carbon atoms and saturated hydrocarbons having 5 carbon atoms, or may contain compounds other than saturated hydrocarbons having 4 carbon atoms and saturated hydrocarbons having 5 carbon atoms, as long as the above-mentioned effects are not impaired. Compounds that can be used as blowing agents other than saturated hydrocarbons having 4 carbon atoms and saturated hydrocarbons having 5 carbon atoms include, for example, organic compounds having a boiling point of 100°C or lower. Examples of such organic compounds include saturated hydrocarbons having 3 or less carbon atoms, such as propane and cyclopropane; saturated hydrocarbons having 6 to 8 carbon atoms, such as hexane and cyclohexane; unsaturated organic compounds having 3 to 6 carbon atoms; hydrofluorocarbons; and hydrofluoroolefins.

[0062] The aqueous medium used in the blowing agent impregnation step may, for example, be water. The aqueous medium may contain, as necessary, a dispersant, a dispersing aid, a surfactant, or the like for dispersing the resin particles in the aqueous medium in the container. Examples of dispersants that can be used include inorganic fine particles such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica. These inorganic fine particles may be used alone, or two or more types of inorganic fine particles may be used in combination. Examples of surfactants that can be used include anionic surfactants such as sodium alkylbenzenesulfonate, sodium dodecylbenzenesulfonate, sodium alkanesulfonate, sodium lauryl sulfate, sodium α-olefinsulfonate, and sodium dodecyldiphenyletherdisulfonate. These surfactants may be used alone, or two or more types of surfactants may be used in combination.

[0063] The aqueous medium may contain an electrolyte, if necessary, consisting of an inorganic salt such as lithium chloride, potassium chloride, sodium chloride, sodium sulfate, sodium nitrate, magnesium sulfate, sodium carbonate, or sodium bicarbonate. To further improve the toughness and mechanical strength of the molded body, it is preferable to add a water-soluble polymerization inhibitor to the aqueous medium. Examples of water-soluble polymerization inhibitors that can be used include sodium nitrite, potassium nitrite, ammonium nitrite, L-ascorbic acid, and citric acid.

[0064] In the foaming agent impregnation step, for example, the resin particles are dispersed in an aqueous medium, and then the foaming agent is added to the aqueous medium, thereby impregnating the resin particles with the foaming agent. From the viewpoint of accelerating the impregnation of the resin particles with the foaming agent, the temperature of the aqueous medium when the foaming agent is impregnated into the resin particles in the foaming agent impregnation step is preferably 105°C or higher and 125°C or lower.

[0065] The average aspect ratio of the expandable particles obtained by the above-mentioned production method is preferably approximately 1.0 or more and 2.0 or less, more preferably 1.0 or more and 1.5 or less. Expandable particles having an average aspect ratio within the above-mentioned specific range are suppressed from flattening. Therefore, by expanding such expandable particles, flattening of the resin foam particles can be suppressed, and resin foam particles with excellent fillability into a molding die can be obtained. Furthermore, by performing in-mold molding using such resin foam particles, it is possible to produce molded articles with good appearance. The average aspect ratio of the expandable particles can be measured using a particle size distribution analyzer based on image analysis (for example, the particle size distribution analyzer "Militrack JPA" manufactured by Nikkiso Co., Ltd.).

[0066] Further, resin expanded beads can be obtained by expanding the expandable beads obtained by the above-mentioned production method. Here, the resin expanded beads are particulate foams. The average aspect ratio of the resin expanded beads is preferably approximately 2.0 or less. The resin expanded beads having an average aspect ratio within the above-mentioned specific range are suppressed from being flattened, and include spherical, ellipsoidal, and shapes similar to these. Therefore, the resin expanded beads having an average aspect ratio within the above-mentioned specific range have excellent mold filling properties. From the viewpoint of producing molded articles with better mold filling properties and better appearance, the average aspect ratio of the resin expanded beads is preferably 1.0 or more and 1.5 or less. The average aspect ratio of the resin expanded beads can be measured in the same manner as the method for measuring the average aspect ratio of the expandable beads described above.

[0067] The internal moisture content of the expandable granules obtained by the above-mentioned production method is preferably 0.5% by mass or less, more preferably 0.3% by mass or less, and even more preferably 0.2% by mass or less. The internal moisture content of the expandable granules can be measured by vaporizing the internal moisture content of the expandable granules using a moisture vaporizer ("CHK-501" manufactured by Kyoto Electronics Manufacturing Co., Ltd.) and introducing the vaporized moisture into a Karl Fischer moisture meter ("MKC-610" manufactured by Kyoto Electronics Manufacturing Co., Ltd.). [Example]

[0068] Examples of the method for producing the expandable granules are described below.

[0069] Example 1 To produce the strands in this example, an extruder with a cylinder diameter of 30 mm was used, and a die lip with four 3.0 mm diameter circular holes was connected to the resin outlet of the extruder. A resin thermometer for measuring the extrusion temperature was also installed between the extruder and the die lip. 100 parts by mass of a styrene-based resin having the number-average molecular weight Mn, weight-average molecular weight Mw, z-average molecular weight Mz, and melt mass-flow rate shown in Table 1, 1 part by mass of talc, and 0.5 parts by mass of ethylene bis(stearic acid amide) were charged into the extruder, melt-kneaded inside the extruder, and the resin melt was extruded through the circular holes in the die lip to form an extrudate.

[0070] The extrusion temperature measured with a resin thermometer was 238°C, and the extruder's output per unit time was 4.0 kg / h. The extrudate was withdrawn at a speed of 20 m / min and cooled by passing it through a water bath at 20°C to produce a cylindrical strand with a diameter of 0.80 mm. Next, the strand was cut into 2 mm lengths using a strand cutter to obtain cylindrical resin particles having the melt mass-flow rates shown in Table 1. The resin particles in this example were produced using recycled styrene-based resin material derived from styrene-based products used as cushioning materials. More specifically, the recycled styrene-based resin material in this example was produced by recovering the cushioning material, reducing its volume to form an ingot, and then pulverizing it into fine particles. In this example, resin particles were stably produced, so the symbol "Good" was entered in the "Resin Particle Manufacturability" column in Table 1.

[0071] Next, 0.6 kg of resin particles were placed in a 3 L container along with 1.6 L of water as an aqueous medium. Next, 0.5 parts by mass of dispersant, 0.04 parts by mass of surfactant, and 1 part by mass of electrolyte were added to the container per 100 parts by mass of resin particles, and the resin particles were dispersed in the aqueous medium. Magnesium pyrophosphate was used as the dispersant, sodium alkylbenzene sulfonate was used as the surfactant, and NaCl·NaNO3 (30% aqueous solution) was used as the electrolyte.

[0072] Next, the container was heated from 40°C to the impregnation temperature shown in Table 1 over 1 hour while stirring. After the temperature inside the container reached the impregnation temperature, 9 parts by mass of butane and 4 parts by mass of pentane were added to 100 parts by mass of resin particles, and the impregnation temperature was maintained for 6 hours, thereby impregnating the resin particles with a blowing agent consisting of butane and pentane. The butane used in this example was a mixture of normal butane and isobutane (more specifically, "Zixis Butane MSZ" manufactured by Zixis Corporation). The pentane used in this example was a mixture of 80% by mass of normal pentane and 20% by mass of isopentane (more specifically, "Mixed Pentane" manufactured by SK Sangyo Co., Ltd.).

[0073] The container was then cooled to 35°C over 7 hours, and the expandable granules were removed from the container. Nitric acid was then added to dissolve the magnesium pyrophosphate adhering to the surface of the expandable granules. The granules were then dehydrated and washed using a centrifuge, and the moisture adhering to the surface was removed using an airflow dryer. The total amount of blowing agent added, the mass ratio of the saturated hydrocarbons with 4 carbon atoms to the sum of the saturated hydrocarbons with 4 carbon atoms and the saturated hydrocarbons with 5 carbon atoms, and the mass ratio of the saturated hydrocarbons with 5 carbon atoms were as shown in Table 1.

[0074] The expandable granules obtained by the above method were placed in a 30 L volume batch expansion machine under atmospheric pressure, and steam at 120°C was supplied into the expansion machine for 120 to 180 seconds to heat the expandable granules, resulting in a bulk density of 14.3 kg / m 3 As shown in Fig. 1, no wrinkles were observed in the resin foam beads 1 of Example 1.

[0075] Furthermore, the resin foam beads were molded in a mold using a molding machine "PEONY-AD / 0907" manufactured by Kasahara Kogyo Co., Ltd. to produce a molded body. Specifically, the resin foam beads were first filled into a mold having a rectangular parallelepiped molding cavity measuring 300 mm in length, 300 mm in width, and 100 mm in thickness. The resin foam beads in the mold were then heated with steam at a gauge pressure of 0.07 MPa (G) for 5 to 15 seconds to produce a molded body. After cooling in the mold for a predetermined time, the molded body was removed from the mold. The molded body removed from the mold was dried at a temperature of 40°C for one day and then further aged at room temperature for at least one day.

[0076] Example 2 The manufacturing methods of the expandable particles, resin expanded particles, and molded bodies in this example are generally the same as those of Example 1, except that the extrusion temperature in the extrusion process was changed to the temperature shown in Table 1, and the length L of the resin particles was changed to the temperature shown in Table 1.

[0077] (Examples 3 and 4) The manufacturing methods of the expandable granules, resin foam granules, and molded articles in these examples were generally the same as those in Example 1, except that the styrene-based resin used in Example 1 was replaced with a styrene-based resin having the number-average molecular weight Mn, weight-average molecular weight Mw, z-average molecular weight Mz, and melt mass-flow rate shown in Table 1. The resin granules in these examples were made using recycled styrene-based resin material derived from refrigerator shelves. The melt mass-flow rates of the resin granules in these examples were as shown in Table 1.

[0078] Examples 5 to 7 The methods for producing the expandable granules, expanded resin granules, and molded articles in these examples were generally the same as those in Example 1, except that the amounts of butane and pentane added were changed as shown in Table 2.

[0079] Example 8 The manufacturing methods of the expandable particles, resin expanded particles, and molded article in this example are generally the same as those in Example 1, except that the length L and outer diameter D of the resin particles were changed as shown in Table 2.

[0080] (Comparative Examples 1 to 3) The manufacturing methods of the expandable particles, resin expanded particles, and molded articles in these comparative examples were generally the same as those in Example 1, except that butane was not used as a blowing agent and the amount of pentane added was changed as shown in Table 3. The expandable particles and resin expanded particles in Comparative Example 1 had a flat shape. Wrinkles occurred on the surface of the resin expanded particles 8 obtained in Comparative Example 2, as shown in FIG. 2. Although not shown in the figure, wrinkles also occurred on the surface of the resin expanded particles obtained in Comparative Example 3, similar to the resin expanded particles of Comparative Example 2.

[0081] Comparative Example 4 The manufacturing methods of the expandable particles, resin expanded particles, and molded articles in this example are generally the same as those in Example 1, except that pentane was not used as a blowing agent and the amount of butane added was changed as shown in Table 3.

[0082] (Comparative Example 5) The manufacturing methods of the expandable particles, resin expanded particles, and molded articles in this example were generally similar to those in Example 1, except that a styrene-based resin having a melt mass-flow rate shown in Table 3 was used instead of the styrene-based resin used in Example 1. More specifically, in this example, an attempt was made to manufacture resin particles using recycled styrene-based resin materials derived from multiple types of styrene-based products. However, with this manufacturing method, it was not possible to stably produce strands when manufacturing the resin particles, and a sufficient amount of resin particles for manufacturing expandable particles could not be produced. Therefore, in this example, the symbol "Poor" was entered in the "Resin particle manufacturability" column in Table 3, and the symbol "-" was entered in the columns for some items for which evaluation, etc., could not be performed.

[0083] Next, the resin particles, expandable particles, expanded resin particles, and molded articles obtained by the above-mentioned methods were used to measure and evaluate the items shown in Tables 1 to 3. The measurement and evaluation methods for the items shown in Tables 1 to 3 were as follows.

[0084] [Molecular weight of styrene-based resin] The number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz) of the styrene-based resin were measured by gel permeation chromatography (GPC) using polystyrene as the standard. Specifically, the styrene-based resin was dissolved in tetrahydrofuran (THF) to prepare a sample solution with a concentration of 0.1% by mass. The styrene-based resin in the sample solution was separated based on molecular weight using a column consisting of one TSKguardcolumn SuperH-H and two TSK-GEL SuperHM-H columns connected in series, with an eluent of tetrahydrofuran (THF) and a THF flow rate of 0.6 mL / min, to obtain a chromatogram. The retention time in the chromatogram was then converted to molecular weight using a calibration curve created using standard polystyrene to obtain a differential molecular weight distribution curve. The number-average molecular weight (Mn), weight-average molecular weight (Mw), and z-average molecular weight (Mz) of the styrene-based resin were calculated from this differential molecular weight distribution curve. The chromatogram was obtained using HLC-8320GPC EcoSEC manufactured by Tosoh Corporation.

[0085] [Melt mass flow rate of styrene resin] The melt mass-flow rate of the styrene resin was measured at a temperature of 200°C and a load of 5 kg in accordance with JIS K7210-1:2014. In Tables 1 to 3, the melt mass-flow rate is abbreviated as "MFR."

[0086] [Length L and outer diameter D of resin particle] The length and outer diameter of 100 randomly selected resin particles were measured using a caliper, and the arithmetic mean values ​​were taken as the length L and outer diameter D of the resin particles. The "L / D" column in Tables 1 to 3 lists the value obtained by dividing the length L of the resin particle thus obtained by dividing the outer diameter D.

[0087] [Lt / Dt change rate of resin particles after heat treatment] The magnitude of residual stress in resin particles used to manufacture expandable granules was evaluated based on the Lt / Dt change rate of the resin particles due to heat treatment. The heat treatment method was as follows: Separately from the blowing agent impregnation process, 0.6 kg of resin particles were placed in a 3 L container along with 1.6 L of water as an aqueous medium. Next, 0.5 parts by mass of dispersant, 0.04 parts by mass of surfactant, and 1 part by mass of electrolyte were added to the container per 100 parts by mass of resin particles to disperse the resin particles in the aqueous medium. Magnesium pyrophosphate was used as the dispersant, sodium alkylbenzene sulfonate as the surfactant, and NaCl·NaNO3 (30% aqueous solution) as the electrolyte. The container was then heated to 115°C without adding a blowing agent and maintained at this temperature for 6 hours. The container was then cooled to a temperature below the softening point of the resin particles, and the heat-treated resin particles were removed.

[0088] The length Lt and outer diameter Dt of the resin particles after heat treatment obtained as described above were measured using the same method as the length L and outer diameter D of the resin particles before heat treatment. The Lt / Dt of the resin particles after heat treatment was calculated by dividing the length Lt of the resin particles after heat treatment by the outer diameter Dt. The "Lt / Dt" column in Tables 1 to 3 shows the Lt / Dt values ​​of the resin particles after heat treatment obtained in this manner. The "Lt / Dt Change Rate" column in Tables 1 to 3 also shows the Lt / Dt change rate (unit: %) due to heat treatment, calculated based on the following formula (1) using the L / D value LD1 of the resin particles before heat treatment and the Lt / Dt value LD2 of the resin particles after heat treatment. Lt / Dt change rate = {(LD2 - LD1) / LD1} × 100 (1) The rate of change is preferably −80% or more and −30% or less, and more preferably −75% or more and −40% or less.

[0089] [Melt mass flow rate of resin particles] The melt mass flow rate of the resin particles was measured at a temperature of 200°C and a load of 5 kg in accordance with JIS K7210-1:2014.

[0090] [Particle size and average aspect ratio of expandable particles] The volumetric particle size distribution of expandable particles was measured and particle shape was evaluated using a particle size distribution analyzer "Militrack JPA" manufactured by Nikkiso Co., Ltd. Specifically, 50 g of expandable particles were allowed to fall freely from the sample feeder of the analyzer, and the projected image of the expandable particles was captured with a CCD camera. Next, the captured image information was subjected to sequential calculations and combination processing, and the volumetric particle size distribution and aspect ratio of each expandable particle were measured under the conditions of an image analysis method that outputs particle size distribution and shape index results.

[0091] The "Average Particle Diameter" column in Tables 1 to 3 lists the cumulative 63% particle size in the volume-based particle size distribution obtained in this manner, i.e., the particle size at which the cumulative volume when accumulating from the smallest particle size is 63%. The "Average Aspect Ratio of Expandable Particles" column in Tables 1 to 3 lists the arithmetic mean of the aspect ratios of 1,000 expandable particles. The aforementioned average particle size and average aspect ratio are physical property values ​​for resin particles prepared by the aforementioned method without classification by sieving or the like. The "Shape of Expandable Particles" column in Tables 1 to 3 lists the shape of the expandable particles determined based on the average aspect ratio of the expandable particles. Specifically, if the average aspect ratio of the expandable particles was 2.0 or less, the shape of the expandable particles was determined to be "spherical," and if the average aspect ratio of the expandable particles was greater than 2.0, the shape of the expandable particles was determined to be "flat."

[0092] [Internal moisture content of expandable granules] The amount of moisture contained inside the expandable particles was measured using a Karl Fischer moisture meter. Specifically, first, water adhering to the surface of the expandable particles was removed. Then, approximately 0.28 g of expandable particles was precisely weighed and used as a sample. The sample was heated at a temperature of 160°C using a moisture vaporizer (Kyoto Electronics Manufacturing Co., Ltd., "CHK-501") to vaporize the moisture in the sample, and the vaporized moisture was introduced into a Karl Fischer moisture meter (Kyoto Electronics Manufacturing Co., Ltd., "MKC-610") to measure the amount of moisture contained inside the expandable particles. The moisture amount was measured by coulometric titration.

[0093] [Amount of styrene monomer] The amount of styrene monomer contained in the expandable particles was measured using a headspace gas chromatograph mass spectrometer. Specifically, three standard solutions were prepared in DMF (dimethylformamide) to give styrene concentrations of 5 ppm by mass, 50 ppm by mass, and 500 ppm by mass. 0.2 g of the standard solution was weighed into a 20 ml vial, and 1 ml of DMF was added and sealed. The gas phase was measured using the gas chromatograph mass spectrometer, and a calibration curve was created from the resulting chromatogram. Next, 0.2 g of expandable particles was weighed out and placed in a 20 ml vial together with 1 ml of DMF, and sealed. This vial was kept at room temperature for one day until the expandable particles were completely dissolved in the DMF. The gas phase of the vial was then measured using the gas chromatograph mass spectrometer, and a chromatogram was obtained. The amount of styrene monomer contained in the expandable particles was determined based on this chromatogram and a previously prepared calibration curve.

[0094] The measurement conditions for gas chromatography mass spectrometry were as follows. Gas chromatograph mass spectrometer: Shimadzu Corporation GCMS-QP2020 Headspace sampler: Shimadzu Corporation HS-20 Capillary column: GL Sciences, Inc., Stabilwax, inner diameter 0.32 mm, length 30 m Headspace sampler incubation conditions: 90°C, 1 hour Column temperature: 50°C x 2 min → (heating rate: 10°C / min) → 90°C → (heating rate: 5°C / min) → 120°C → (heating rate: 20°C / min) → 230°C x 2 min Ion source temperature: 200℃ Carrier gas: Helium, column flow rate: 2 ml / min Split ratio: 1 / 10

[0095] [Bulk density of expanded resin particles] First, the resin foam beads were left to stand for 24 hours or more in an environment of 50% relative humidity, 23°C temperature, and 1 atm atmospheric pressure to condition the resin foam beads. After conditioning, the resin foam beads were filled into a measuring cylinder, and the bottom of the measuring cylinder was lightly tapped on the floor several times to stabilize the filling height of the resin foam beads in the measuring cylinder. The bulk volume (unit: L) of the resin foam beads was read from the graduations on the measuring cylinder. Then, the mass (unit: g) of the resin foam beads in the measuring cylinder was divided by the aforementioned bulk volume, and the bulk density (unit: kg / m) of the resin foam beads was calculated by converting the unit. 3 ) was obtained.

[0096] [Bubble state of resin foam particles] The bubble state of the resin foam beads was evaluated based on the coefficient of variation of the bubble diameter of the resin foam beads. The bubble diameter of the resin foam beads was measured as follows. First, the resin foam beads were divided into roughly two equal parts. Next, a magnified photograph of the cut surface was taken using a scanning electron microscope so that the entire cut surface exposed by the division was within the field of view. A starting point was set near the center of the cut surface of the resin foam beads in the magnified photograph obtained in this way, and eight line segments were drawn from the starting point to the edge of the cut surface, i.e., the surface of the resin foam beads, so that the angles between adjacent line segments were equal. In other words, eight line segments were drawn from the starting point so that the angles between adjacent line segments were 45°. The total length of the eight line segments was then divided by the total number of bubbles intersecting these lines to calculate the bubble diameter (unit: μm) of each resin foam bead.

[0097] The above procedure was performed on 20 resin foam beads, and the average cell diameter (unit: μm) and standard deviation (unit: μm) of the resin foam beads were calculated based on the cell diameters of the 20 resin foam beads. The average cell diameter of the resin foam beads is specifically the arithmetic mean value of the cell diameters of the 20 resin foam beads. The standard deviation of the cell diameters of the resin foam beads is specifically the square root of the unbiased variance of the cell diameters. The ratio of the standard deviation to the average cell diameter of the resin foam beads obtained in this way was expressed as a percentage to calculate the coefficient of variation of the cell diameter (unit: %).

[0098] The smaller the coefficient of variation of cell diameter, the smaller the variation in cell diameter in the expanded resin beads, indicating a better cell state. In the "Cell State" column of Tables 1 to 3, the symbol "A" is entered when the coefficient of variation of cell diameter is less than 30%, the symbol "B" is entered when it is 30% or more but less than 50%, and the symbol "C" is entered when it is 50% or more.

[0099] [Average aspect ratio of resin foam particles] The method for measuring the average aspect ratio of the resin foam particles was the same as that for measuring the average aspect ratio of the expandable particles described above, except that the measurement was performed using resin foam particles instead of expandable particles. The "Shape of Resin Foam Particles" column in Tables 1 to 3 lists the shape of the resin foam particles determined based on the average aspect ratio of the resin foam particles. Specifically, if the average aspect ratio of the resin foam particles was 2.0 or less, the shape of the resin foam particles was determined to be "spherical," and if the average aspect ratio of the resin foam particles was greater than 2.0, the shape of the resin foam particles was determined to be "flat."

[0100] [Density of Molded Product] Density of the compact (unit: kg / m 3 ) is obtained by dividing the mass (unit: g) of the molded body by the volume (unit: L) determined from the outer dimensions of the molded body, and then converting the unit.

[0101] [Moldability] The surface of the molded body was visually observed, and the moldability was evaluated based on the results. The specific evaluation method was as follows.

[0102] Surface voids A 100 mm x 100 mm square was drawn in the center of the skin surface of the molded article, i.e., the surface that was in contact with the mold during in-mold molding. A diagonal line was then drawn from one corner of this square. The number of voids present on the diagonal line, i.e., the number of voids with dimensions of 1 mm x 1 mm or greater among the gaps formed between the foamed resin particles, was then counted. In the "Surface Voids" column of Tables 1 to 3, the symbol "A" was entered if the number of voids was 3 or less, the symbol "B" was entered if the number was 4 to 10, and the symbol "C" was entered if the number was 11 or more.

[0103] Wrinkles The skin surface of the molded body was visually observed to evaluate the presence or absence of wrinkles. In the "Wrinkles" column of Tables 1 to 3, the symbol "A" was entered when no wrinkles occurred, the symbol "B" was entered when slight wrinkles occurred, and the symbol "C" was entered when wrinkles were noticeable.

[0104] [Flexural strength] The mechanical strength of the molded body was evaluated based on the bending strength of the molded body in a three-point bending test. For the bending strength measurement, rectangular parallelepiped test pieces measuring 350 mm long x 65 mm wide x 25 mm thick were used, obtained by cutting the molded body. The three-point bending test was conducted in accordance with JIS K 7221-2 Appendix 1.

[0105] [10% compressive strength] A rectangular parallelepiped test piece measuring 50 mm in length, 50 mm in width, and 25 mm in thickness was taken from the center of the compact. A compression test was conducted on the test piece based on the method specified in JIS K7220:2006, and a stress-strain curve was obtained. The stress at a strain of 10% on the stress-strain curve was defined as the 10% compressive strength. The compression test was conducted in a laboratory at 23°C.

[0106] [Table 1]

[0107] [Table 2]

[0108] [Table 3]

[0109] As shown in Tables 1 and 2, the extrusion temperature, melt mass-flow rate of the resin particles, amount of blowing agent added, and mass ratio of saturated hydrocarbons having 4 carbon atoms to saturated hydrocarbons having 5 carbon atoms in the blowing agent in Examples 1 to 8 are all within the specified ranges. Therefore, the expandable particles in these Examples are suppressed from flattening and have a spherical shape. Furthermore, by expanding the expandable particles obtained in these Examples, resin expanded particles that are suppressed from flattening and have no wrinkles on the surface can be obtained. Furthermore, by molding the resin expanded particles obtained in this manner in a mold, a molded product with few wrinkles and surface voids and a good appearance can be obtained.

[0110] In contrast, as shown in Table 3, in Comparative Example 1, the amount of saturated hydrocarbons having four carbon atoms or saturated hydrocarbons having five carbon atoms contained in the blowing agent was insufficient, so the resin particles shrunk excessively in the blowing agent impregnation step, resulting in a flattened shape of the expandable particles. Furthermore, the expanded resin particles obtained by expanding the expandable particles also had a flattened shape. Furthermore, the expanded resin particles obtained in this manner had poor mold filling properties and poor secondary foaming properties, resulting in the formation of a relatively large number of voids on the surface of the molded article obtained after in-mold molding.

[0111] In Comparative Example 2, the amount of saturated hydrocarbon having 5 carbon atoms added was increased compared to Comparative Example 1, thereby obtaining expandable particles in which flattening was suppressed. However, the increased amount of saturated hydrocarbon having 5 carbon atoms added caused wrinkles to form on the surfaces of the expanded resin beads and the surfaces of the molded article. Furthermore, secondary expansion of the expanded resin beads during in-mold molding was insufficient, resulting in the formation of a relatively large number of voids on the surfaces of the molded article.

[0112] In Comparative Example 3, the amount of saturated hydrocarbon having 5 carbon atoms added was increased more than in Comparative Example 2, which improved the secondary expandability of the expanded resin beads and prevented the formation of voids on the surface of the molded article. However, increasing the amount of saturated hydrocarbon having 5 carbon atoms caused wrinkles to form on the surface of the expanded resin beads and the surface of the molded article.

[0113] In Comparative Example 4, since the foaming agent did not contain a saturated hydrocarbon having a carbon number of 5, wrinkles were formed on the surfaces of the foamed resin beads and the surface of the molded article. In addition, secondary expansion of the foamed resin beads during molding in the mold was insufficient, and a relatively large number of voids were formed on the surface of the molded article.

[0114] The above describes the aspects of the method for producing expandable particles based on examples, but the specific aspects of the method for producing expandable particles according to the present invention are not limited to the aspects of the examples, and the configuration can be changed as appropriate within the scope that does not detract from the spirit of the present invention. [Explanation of symbols]

[0115] 1. Resin foam particles

Claims

1. a resin particle production step of heating a styrene-based resin to form a resin melt, extruding the resin melt to form strands, and then cutting the strands to obtain resin particles; a blowing agent impregnation step of impregnating the resin particles dispersed in the aqueous medium with a blowing agent to obtain expandable particles, the resin particles have a melt mass flow rate of 0.5 g / 10 min or more and 20 g / 10 min or less, as measured under conditions of a temperature of 200° C. and a load of 5 kg; the amount of the foaming agent added is 8 parts by mass or more and 16 parts by mass or less with respect to 100 parts by mass of the resin particles, the blowing agent comprises a saturated hydrocarbon having 4 carbon atoms and a saturated hydrocarbon having 5 carbon atoms, a mass ratio of the saturated hydrocarbon having 4 carbon atoms to the saturated hydrocarbon having 5 carbon atoms in the blowing agent of 20:80 to 90:10;

2. 2. The method for producing expandable granules according to claim 1, wherein a mass ratio of the saturated hydrocarbon having 4 carbon atoms to the saturated hydrocarbon having 5 carbon atoms in the blowing agent is 60:40 to 90:

10.

3. The method for producing expandable granules according to claim 1 or 2, wherein the styrene-based resin includes a styrene-based resin derived from a recycled styrene-based resin material.

4. 3. The method for producing expandable granules according to claim 1, wherein the resin granules have a cylindrical shape, and a ratio (L / D) of a length L of the resin granules to an outer diameter D of the resin granules is 1.5 or more and 4.0 or less.

5. 3. The method for producing expandable particles according to claim 1 or 2, wherein in the resin particle production step, a styrene-based resin and talc and / or ethylene bisstearic acid amide are heated to form a resin melt, the resin melt is extruded to form strands, and then the strands are cut to obtain resin particles.

6. 3. The method for producing expandable granules according to claim 1, wherein the temperature of the aqueous medium when the blowing agent is impregnated into the resin granules in the blowing agent impregnation step is 105°C or higher and 125°C or lower.

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