Foamed bead, method for producing such bead, and method for producing molded component

Abstract

The present invention relates to a foamed bead having a foam structure, a method for producing such a bead, and a method for producing a molded component using the bead. The present invention relates to a foamed bead having a foam structure, the foamed bead having a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and having an angle of repose value of 31.0°-50.0° as measured in accordance with ISO 4324.

Description

Foamed beads, method for producing the beads, and method for producing molded parts

[0001] The present invention relates to foamed beads having a cellular structure, a method for producing the beads, and a method for producing a molded article using the beads.

[0002] Foam beads having a cellular structure are generally known and may be made of polyolefins such as polyethylene (PE) and / or polypropylene (PP).

[0003] A typical characteristic of foam beads is that they can maintain properties such as flexibility and shock absorption while maintaining low density. Foam beads with this property are useful for producing lightweight parts for a variety of applications. Examples of molded articles made from foam beads include those used in construction and civil engineering, transportation (especially automobiles), and sporting goods.

[0004] Foamed beads are typically lighter foamed beads obtained by a primary expansion process, in which raw material beads (hereinafter referred to as "resin particles") are initially expanded using an extrusion foaming process or a batch expansion process using an autoclave, followed by a pre-expansion process. These foamed beads are used to produce molded articles. Conventionally, the pre-expansion process involves further heating resin particles (hereinafter referred to as "first-stage expanded resin particles") that have already been expanded with steam to expand the gas within the cells within the first-stage expanded resin particles. For example, Patent Document 1 describes a two-stage method for producing expanded polypropylene resin particles, in which polypropylene resin particles are impregnated with dichlorodifluoromethane as a blowing agent at a temperature of 30 to 75°C, and then heated to perform the first stage of expansion. Then, a gas containing nitrogen as the main component is added to impart expandability, and the second stage of expansion, equivalent to the pre-expansion process, is performed by, for example, steam heating. However, this method requires the use of heated steam, which can result in significant energy consumption, investment in a dedicated vacuum line, and the need for qualified personnel to operate the vacuum line.

[0005] In recent years, the pre-expansion process has been further investigated to improve the environmental sustainability of the conventional steam-based pre-expansion process, and in particular, methods have been developed that apply thermal energy to the beads by radiating infrared rays or the like.

[0006] When first-stage expanded resin beads are expanded in the pre-expansion step, it is very important that the first-stage expanded resin beads can absorb sufficient energy to expand in the pre-expansion step when a specific amount of energy is applied to the first-stage expanded resin beads. Experiments by the present inventors have shown that the energy absorption characteristics of the first-stage expanded resin beads have a significant effect on their expansion characteristics, and as a result, have a significant effect on other properties of the resulting expanded beads, such as their shape.

[0007] The shape of the foamed beads is very important for efficiently processing the foamed beads to produce high quality products because the shape affects manufacturing process parameters, such as the packing characteristics of the foamed beads in the mold used to form the product. The use of such beads having a substantially spherical shape for molding typically results in improved packing characteristics.

[0008] Furthermore, applying thermal energy to the first-stage expanded resin particles by irradiating them with infrared rays or the like can improve the environmental sustainability of the pre-expansion process. However, there remains room for further improvement in the foamed beads and their manufacturing methods in terms of cycle time and production efficiency when using the foamed beads to produce molded articles. Therefore, there remains a need for foamed beads and methods for manufacturing such beads that address at least some of the above-mentioned problems and drawbacks.

[0009] Japanese Patent Application Publication No. 58-136634

[0010] Accordingly, a primary object of the present invention is to provide improved foamed beads having a cellular structure, a method for producing the same, and a method for producing molded articles using the same. In particular, it is believed that improving the foamed beads having a cellular structure will lead to improvements in the method for producing the same and the method for producing molded articles using the same.

[0011] A first aspect of the present disclosure for achieving the above object is expanded beads having a cellular structure, which have a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and which have an angle of repose of 31.0° to 50.0° as measured in accordance with ISO 4324.

[0012] In order to achieve the above object, a second aspect of the present disclosure is a method for producing expanded beads having a cellular structure, comprising the steps of: supplying first-stage expanded resin particles having a first angle of repose onto a conveying device; and moving the conveying device relative to at least one heating device, which applies thermal energy to the first-stage expanded resin particles by radiating infrared rays, thereby producing expanded beads having a cellular structure, wherein the expanded beads have a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and have an angle of repose of 31.0° to 50.0° measured in accordance with ISO 4324, and the first-stage expanded resin particles comprise a polymer material and at least one additive, and the additive exhibits a higher absorption rate of infrared rays than the polymer material.

[0013] A third aspect of the present disclosure for achieving the above object is an aggregate of a particulate polymer material including the expanded beads of the first aspect. A fourth aspect of the present disclosure for achieving the above object is a method for producing a molded article using the expanded beads of the first aspect, the method comprising at least the following steps: supplying the expanded beads to a cavity of a molding die; and performing molding using the expanded beads to produce a molded article.

[0014] According to the present disclosure, it is possible to provide improved foamed beads having a cellular structure, a method for producing the beads, and a method for producing a molded article by processing the beads.

[0015] 1 is a cross-sectional view of an expanded bead according to an embodiment of the present disclosure; FIG. 2 is a principle diagram showing an exemplary manufacturing method for the expanded bead according to an embodiment of the present disclosure and an embodiment of the expanded bead according to the manufacturing method; FIG. 3 is a diagram showing a typical DSC curve for measuring a high-temperature peak area according to an embodiment of the present disclosure;

[0016] A first aspect of the present disclosure is expanded beads. The beads include an outer shell or wall and a plurality of closed cells present within the outer shell or wall. The beads are typically produced by expanding raw material unexpanded resin particles to obtain first-stage expanded resin particles, which are then further expanded in a pre-expansion step. In the pre-expansion step, energy, particularly thermal energy, is applied to the first-stage expanded resin particles. More specifically, thermal energy is applied to the first-stage expanded resin particles by irradiating them with infrared rays, thereby generating closed cells in the expanded beads.

[0017] Resin particles, particularly unexpanded resin particles, are usually treated in a primary expansion step in which they are expanded by temperature and / or pressure in, for example, an autoclave before undergoing the pre-expansion step. That is, the expanded beads of the present disclosure can usually be obtained through both the primary expansion step and the pre-expansion step.

[0018] Expanded beads have a spherical shape and exhibit a high degree of sphericity, as defined by a sphericity φ greater than 0.94 and less than 1.00. The shape of the expanded beads is close to the geometrically defined shape of a perfect sphere (true sphere), but is not a perfect sphere. As described in detail below, expanded beads have one or more flat surfaces, which makes the shape of the beads less than a perfect sphere. In other words, the presence of one or more flat surfaces makes the expanded beads less than a perfect sphere. The shape of the expanded beads is indicated by a sphericity value greater than 0.94 and less than 1.00, as described above. The sphericity φ of expanded beads refers to the average value of the sphericities of multiple beads. Sphericity can be calculated by dividing the measured surface area of ​​a particle by the surface area of ​​a sphere having the same volume as the particle. Alternatively, sphericity can be calculated by determining the equivalent diameter (Heywood diameter) and the diameter of the smallest circumscribed circle from a projected image of the particle, and then dividing the equivalent diameter by the diameter of the smallest circumscribed circle. The method for measuring the surface area of ​​particles is not particularly limited, but examples thereof include measuring the particle diameter by laser diffraction and calculating the particle surface area based on the measured particle diameter.The method for measuring the volume of particles is not particularly limited, but examples thereof include measurement by laser diffraction.In addition, the area circle equivalent diameter (Heywood diameter) and the circumscribed minimum circle can be determined by taking an enlarged image of the particle using an electron microscope or optical microscope and using image analysis software based on the taken image.The sphericity of foamed beads can be measured, for example, using a particle size distribution measuring device (e.g., Microtrac PartAn 3D manufactured by Microtrac Bell Co., Ltd.).The number of beads used for measurement is, for example, 2000 or more.

[0019] Here, the term "flat portion" refers to a substantially planar region present on the surface of the expanded bead. The term "substantially planar region" refers to a region on the bead that approximates a flat surface. The flat portion is defined by the relationship between the radius of curvature of the curved surface of the bead and the radius of the bead. For example, the flat portion refers to a region where the radius of curvature of the curved surface of the bead is 10 times or more the radius of the bead. The flat portion may be a substantially planar region where the radius of curvature of the curved surface of the expanded bead is 10 times or more, 100 times or more, 1000 times or more, or 10,000 times or more the radius of the bead. As described below, the flat portion is formed at the contact surface between the support surface of the conveying device or the like and the first-stage expanded resin particles because the first-stage expanded resin particles undergo a pre-expansion process in which the first-stage expanded resin particles are irradiated with infrared light while being placed and supported on a substantially planar structure such as a conveying device. The radius of the expanded beads can be calculated based on the particle diameter measured using, for example, a particle size distribution analyzer (e.g., Microtrac PartAn 3D manufactured by Microtrac Bell Corporation).

[0020] Furthermore, the expanded beads have an angle of repose of 31.0° to 50.0° as measured in accordance with ISO 4324. The angle of repose is generally defined as the steepest angle at which the beads can be piled down a funnel without collapsing, and is measured as the inclination of the pile of beads relative to the horizontal surface on which it rests. The angle of repose is thought to be at least indirectly affected by the shape of the expanded beads. That is, the shape of the expanded beads can affect the angle of repose of the expanded beads. In particular, the aforementioned flat surface can affect the angle of repose of the expanded beads.

[0021] As mentioned above, the angle of repose of the expanded beads is measured according to ISO 4324, available at, for example, https: / / www.dinmedia.de / en / standard / iso-4324 / 628873. An apparatus for measuring the angle of repose according to ISO 4324 is available, for example, from Landgraf Laborsysteme HLL GmbH, Magdeburger Strasse 3, 30855 Langenhagen, Germany (URL: https: / / www.hallflowmeter.de / 12 / 158 / AD223 / TDUwNTY2MDcw / 223-L50566070-landgrafhll.html?sid=c69jj62j69pkptk4asdegi3s37). To prevent adverse effects of static electricity during measurement, the measuring apparatus can be grounded and an ion gun can be used to remove excess static electricity remaining on the bead surface. The ion gun is commercially available, for example, from EXAIR, Inc. (11510 Goldcoast Drive, Cincinnati, Ohio 45249-1621, USA) under the trade name 8193 Gen4 Ion Air Gun.

[0022] Experiments conducted by the present inventors have shown that a sphericity of more than 0.94 and less than 1.00 and an angle of repose of 31.0° to 50.0° improves the processing, particularly molding, properties of the foamed beads. In particular, it is believed that the molding properties of the foamed beads in the molding process, in which the foamed beads are filled into a mold cavity and thermal energy, such as steam, is applied to form a molded product, can be improved based on the shape of the foamed beads.

[0023] In fact, the sphericity of the expanded beads of the present disclosure indicates that the beads have good flowability. They also have a pleasing appearance when viewed with the naked eye. The large angle of repose of the expanded beads allows them to be placed in a mold in a different manner than conventional expanded beads, for example, by forming specific voids between the beads. It is believed that the presence of such voids allows for more rapid adjustment of the pressure inside the mold to the external atmosphere during the molding process, thereby shortening the cycle time during the molding process.

[0024] According to one embodiment, the lower limit of the sphericity of the expanded beads is, for example, 0.95 or 0.96. Therefore, the sphericity of the expanded beads is, for example, 0.95 or more and less than 1.00, or 0.96 or more and less than 1.00.

[0025] In another embodiment, the angle of repose of the expanded beads has a range between, for example, at least one of 31.5°, 32.0°, 32.5°, 33.0°, 33.5°, 34.0°, 34.5°, 35.0°, 35.5°, 36.0°, 36.5°, or 37.0° as a lower limit and at least one of 49.5°, 49.0°, 48.5°, 48.0°, 47.5°, 47.0°, 46.5°, 46.0°, 45.5°, 45.0°, 44.5°, 44.0°, 43.5°, 43.0°, 42.5°, 42.0°, 41.5°, 41.0°, 40.5°, or 40.0° as an upper limit. Therefore, the angle of repose of the expanded beads is, for example, 33.0° to 45.0°. Note that 33.0° is an example of the lower limit of the range of the angle of repose, and 45.0° is an example of the upper limit of the range of the angle of repose. In this way, the expanded beads may have a wide range of angles of repose, which means that there is high flexibility in terms of the behavior and related properties of the beads during the pre-expansion process and / or molding process. All of the aforementioned angle of repose values ​​are measured in accordance with ISO 4324.

[0026] In another embodiment, the density (bulk density) of the expanded beads is, for example, 10 kg / m ３ , 11 kg / m ３ , 12 kg / m ３ , 13 kg / m ３ , 14 kg / m ３ , 15 kg / m ３ , 16 kg / m ３ , 17 kg / m ３ , 18 kg / m ３ , 19 kg / m ３ At least one of the following is the lower limit, and for example, 60 kg / m ３ , 59 kg / m ３ , 58 kg / m ３ , 57 kg / m ３ , 56 kg / m ３ , 55 kg / m ３ , 54 kg / m３ , 53 kg / m ３ , 52 kg / m ３ , 51 kg / m ３ , 50 kg / m ３ , 49 kg / m ３ , 48 kg / m ３ , 47 kg / m ３ , 46 kg / m ３ , 45 kg / m ３ , 44 kg / m ３ , 43 kg / m ３ , 42 kg / m ３ , 41 kg / m ３ , 40 kg / m ３ , 39 kg / m ３ , 38 kg / m ３ , 37 kg / m ３ , 36 kg / m ３ , 35 kg / m ３ , 34 kg / m ３ , 33 kg / m ３ , 32 kg / m ３ , 31 kg / m ３ , 30 kg / m ３ , 29 kg / m ３ , 28 kg / m ３ , 27 kg / m ３ , 26 kg / m ３ , 25 kg / m ３ , 24 kg / m ３ , 23 kg / m ３ , 22 kg / m ３ , 21 kg / m ３ , 20 kg / m ３ Therefore, the density of the foamed beads can be, for example, 12 to 40 kg / m ３Thus, expanded beads can have a wide range of densities, which means that there is great flexibility in terms of the behavior and related properties of the beads during the pre-expansion and / or molding processes. The density of the beads can be determined by the following procedure: to measure out 1 liter of beads, a large amount of beads is placed in a 1 liter measuring cylinder in a natural pile up to the 1 liter mark. The mass of the placed beads is measured, and the obtained mass value W2 [g] is divided by the placed volume V2 (1 liter) to obtain the value of W2 / V2. The unit of W2 / V2 is kg / m ３ The density (bulk density) of the beads is calculated by converting the density into kJ / cm2.

[0027] The density of the expanded beads may also be related to the expansion ratio of the beads. For example, the expansion ratio of the expanded beads is 10 to 100, preferably 20 to 80, and more preferably 25 to 75. This indicates that the expanded beads have a low density, making them suitable for producing lightweight parts, for example. The expansion ratio of the expanded beads is determined by the density [kg / m] of the polymer material of the expanded beads. ３ ] is the bulk density of the foamed beads [kg / m ３ ] is the value obtained by dividing by

[0028] In another embodiment, the foam beads comprise a polymeric material and at least one additive. The polymeric material may represent a matrix within which the at least one additive is contained. The at least one additive may be or include, for example, a particulate material. The at least one additive may be a functional additive capable of imparting at least one specific function or characteristic to the beads, such as a cell nucleation function or characteristic, a flame retardant function or characteristic, a thermally conductive function or characteristic, an electrically conductive function or characteristic, a magnetic function or characteristic, or a light absorbing function or characteristic. Thus, the at least one additive may be or include, for example, a cell nucleation additive, a flame retardant additive, a thermally conductive additive, an electrically conductive additive, a magnetic additive, or a light absorbing additive.

[0029] Therefore, in another embodiment, the foam beads comprise a polymer material and at least one light-absorbing additive capable of absorbing light. In particular, the at least one light-absorbing additive is preferably one that absorbs light in the infrared wavelength region. The at least one light-absorbing additive preferably absorbs light at wavelengths ranging from 750 nm to 8 μm, particularly from 1 μm to 4 μm. When a light-absorbing additive is used in the pre-expansion step, the wavelength range of 750 nm to 8 μm, particularly from 1 μm to 4 μm, is particularly preferred because it typically corresponds to the infrared wavelengths used in the pre-expansion step and provides very high efficiency.

[0030] For example, the at least one light-absorbing additive exhibits high absorbance, for example, of at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, or at least 90% for light in the wavelength range of 750 nm to 8 μm, particularly 1 μm to 4 μm. Light having a wavelength range of 750 nm to 8 μm, particularly 1 μm to 4 μm, is typically used in the pre-expansion process in which first-stage expanded resin particles are exposed to infrared radiation for the purpose of inducing pre-expansion. Therefore, the light absorption characteristics of the at least one light-absorbing additive can be selected in relation to the pre-expansion process of each individual first-stage expanded resin particle. The method for measuring the absorbance of the at least one light-absorbing additive is not particularly limited, and examples include techniques such as spectrophotometry, which measures the absorption of light over a specific wavelength range using a UV-Vis-NIR or Fourier transform infrared (FTIR) spectrophotometer.

[0031] Typically, the at least one light absorbing additive exhibits a higher absorption of infrared radiation than the polymeric material, for example, the at least one light absorbing additive exhibits an absorption of infrared radiation that is at least 10%, at least 15%, at least 20%, at least 25%, at least 30%, at least 35%, at least 40%, at least 45%, at least 50%, at least 55%, at least 60%, at least 65%, at least 70%, at least 75%, at least 80%, at least 85%, at least 90%, at least 95%, or at least 100% greater than the absorption of the polymeric material in the corresponding wavelength region.

[0032] In another embodiment, the content of the at least one light absorbing additive is, for example, 0.1 wt %, 0.2 wt %, 0.3 wt %, 0.4 wt %, 0.5 wt %, 0.6 wt %, 0.7 wt %, 0.8 wt %, 0.9 wt %, 1.0 wt %, 1.5 wt %, or 2.0 wt % at the lower limit and, for example, 10.0 wt %, 9.5 wt %, 9.0 wt %, 8.5 wt %, 8.0 wt %, 7.5 wt %, 7.0 wt %, 6.5 wt %, or 6.0 wt % at the upper limit. Thus, the content of the at least one light absorbing additive is, in order of preference, 0.1 wt% to 10.0 wt%, 0.2 wt% to 9.5 wt%, 0.3 wt% to 9.0 wt%, 0.4 wt% to 8.5 wt%, 0.5 wt% to 8.0 wt%, 0.6 wt% to 7.5 wt%, 0.7 wt% to 7.0 wt%, 0.8 wt% to 6.5 wt%, 0.9 wt% to 6.0 wt%, 1.0 wt% to 6.0 wt%, 1.5 wt% to 6.0 wt%, and 2.0 wt% to 6.0 wt%. For example, the content of the at least one light absorbing additive is 0.1 wt% to 10.0 wt%.

[0033] In another embodiment, the at least one light absorbing additive may be, for example, one or more organic and / or inorganic pigments (dyes). The at least one light absorbing additive is or may comprise a pigment that typically absorbs light in a specific wavelength range (as specified above, typically a wavelength range including wavelengths from 750 nm to 8 μm, particularly 1 μm to 4 μm).

[0034] Examples of inorganic pigments include chromates such as lead chromate (yellow), zinc chromate (yellow), and barium chromate (yellow), ferrocyanides such as Prussian blue (dark blue), sulfides such as cadmium sulfide (yellow) and cadmium sulfide selenide (red), oxides such as iron oxide (red, yellow, and brown) and titanium dioxide (white), and silicates such as ultramarine blue. Examples of organic pigments include azo pigments such as monoazo pigments, diazo pigments, azo lakes, and condensed azo pigments, and polycyclic pigments such as phthalocyanines (blue and green), anthraquinones (red), perylenes (red), perinones (orange), thioindigo (purple), quinacridones (red), dioxazines (purple), isoindolinones (yellow), and quinophthalones (yellow).

[0035] In another embodiment, the at least one light absorbing additive may be or include a black inorganic pigment comprising carbon particles, such as one or more materials selected from carbon black, conductive carbon, graphene, graphite, and carbon nanostructures, such as tubes, layers, and the like.

[0036] According to specific embodiments, the at least one light absorbing additive is or includes carbon black. Carbon black is useful as a light absorbing additive because it not only exhibits high absorption in the wavelength range of 750 nm to 8 μm, particularly inclusive of 1 μm to 4 μm, but also because it is a readily available, relatively cost-effective material and its processing characteristics, particularly in relation to beads, are generally well understood, including excellent dispersibility in polymer resins. Examples of carbon black include, but are not limited to, channel black, roller black, furnace black, thermal black, acetylene black, and ketjen black.

[0037] One or more light absorbing additives other than carbon black may additionally or alternatively be used.

[0038] Other exemplary light absorbing additives that are not pigments are also contemplated, such as specialized near-infrared absorbers, including, but not limited to, metal oxides and sulfides such as tungsten oxide, tin oxide, antimony oxide, lead sulfide, and the like, or mixtures and / or compounds thereof.

[0039] As mentioned above, each foamed bead has an outer shell or wall and closed cells residing within the shell or wall.

[0040] In another embodiment, at least a portion of the entire foamed beads, particularly substantially all of the foamed beads, may have at least one flat portion and two sidewall portions extending from the flat portion as shown in Fig. 1 in a cross section taken along a plane perpendicular to two parallel planes that pass through the center of the bead and sandwich the base, with the flat portion of the bead as the base. The center of the bead here means the center of gravity of the bead.

[0041] The flat portion of the expanded bead can be formed by undergoing a pre-expanding process in which first-stage expanded resin particles are irradiated with infrared rays while being placed and supported on a (substantially) planar structure such as a conveying device. In another embodiment, when the flat portion of the bead is taken as the bottom surface, the sidewall portion of the expanded bead can extend at an angle to at least one flat portion in a cross section taken along a plane perpendicular to two parallel planes that pass through the center of the bead and sandwich the bottom surface at the smallest distance. The angle may be, for example, in the range of 90° to 160°, 95° to 150°, or 100° to 140°. The center of the bead referred to here is the center of gravity of the bead.

[0042] In another embodiment, the length of the base of the bead in the cross section may be, for example, 150 μm to 7000 μm, 500 μm to 4000 μm, 750 μm to 3500 μm, or 1000 μm to 3000 μm. The length of the base usually corresponds to the distance between both ends of at least one of the bases in the cross section.

[0043] In another embodiment, the length of the base of the bead in the cross section may be a length corresponding to 20 to 80%, 22 to 75%, 25 to 70%, 27 to 65%, or 30 to 60% of the parallel diameter of the bead. The parallel diameter of the bead corresponds to the length of a line segment formed by the intersection of a straight line passing through the center of the cross section and parallel to the two parallel planes that are the smallest distance apart, and the periphery of the cross section of the bead, when the flat portion of the bead is taken as the base and the bead is cut perpendicularly to the two parallel planes that pass through the center of the cross section. The center of the bead referred to here is the center of gravity of the bead.

[0044] The aforementioned dimensions of the beads can be evaluated using, for example, a microscope VHX-6000 sold by Keyence Corporation (1-3-14 Higashinakajima, Higashiyodogawa-ku, Osaka City, Osaka Prefecture, Japan, 533-8555).

[0045] In another embodiment, the polymer material of the foam beads is or includes a polyolefin resin or a polyamide resin. The term "polyolefin resin" particularly refers to polypropylene resin, polyethylene resin, and mixtures thereof, and the term "polyamide resin" particularly refers to polyamide resin. The content of the polyolefin resin or polyamide resin in the polymer material is, in order of preference, at least 50% by weight, at least 55% by weight, at least 60% by weight, at least 65% by weight, at least 70% by weight, at least 75% by weight, at least 80% by weight, at least 85% by weight, at least 90% by weight, at least 95% by weight, or 100% by weight. The polyolefin resin refers to a polyolefin homopolymer or a polyolefin copolymer. Examples of polyolefin homopolymers include polyethylene and polypropylene (e.g., isotactic polypropylene, syndiotactic polypropylene, and atactic polypropylene).

[0046] The polyolefin copolymer may be based on or comprise, for example, at least one ethylene-based copolymer and / or at least one propylene-based copolymer, and may be, for example, a random copolymer or a block copolymer, with random copolymers being particularly preferred.

[0047] The method for producing the polyolefin resin is not particularly limited. In particular, for example, the use of a catalyst system such as a Ziegler-Natta polymerization catalyst or a metallocene polymerization catalyst is considered for the production of the polyolefin resin.

[0048] Examples of polypropylene-based resins include, but are not limited to, polypropylene homopolymers and propylene-based copolymers containing more than 50% by mass of propylene monomers. The polypropylene copolymers may be, for example, random copolymers or block copolymers, and may contain them, with random copolymers being particularly preferred.

[0049] Examples of propylene-based copolymers include, but are not limited to, copolymers of propylene with ethylene and / or at least one α-olefin having 4 to 20 carbon atoms. Examples of ethylene-based copolymers include, but are not limited to, copolymers of ethylene with propylene and / or at least one α-olefin having 4 to 20 carbon atoms. Examples of α-olefins having 4 to 20 carbon atoms include, but are not limited to, 1-butene, 1-pentene, 1-hexene, 1-octene, and 4-methyl-1-butene.

[0050] The propylene monomer content in the propylene copolymer is preferably 80% by weight or more, more preferably 90% by weight or more. The propylene monomer content in the propylene copolymer is preferably 99% by weight or less, more preferably 98% by weight or less. The ethylene monomer content in the ethylene copolymer is preferably 80% by weight or more, more preferably 90% by weight or more, even more preferably 95% by weight or more, and even more preferably 98% by weight or more.

[0051] Examples of propylene copolymers include impact-resistant polypropylenes (block polypropylenes) consisting of two or more phases including a continuous phase of propylene polymer and a rubber phase such as an ethylene-α-olefin copolymer present as a dispersed phase in the continuous phase. When the propylene copolymer contains an ethylene-derived component (ethylene component) and / or a butene-derived component (butene component) as a comonomer, the moldability of the beads under low molding pressure conditions can be further improved.

[0052] When the propylene-based copolymer contains ethylene as a comonomer, the ethylene content in the propylene-based copolymer is, in order of preference, 1 to 15 wt%, 2 to 15 wt%, and 3 to 15 wt%. When the propylene-based copolymer contains ethylene and butene as comonomers, the total amount of ethylene and butene in the propylene-based copolymer is, in order of preference, 1 to 15 wt%, 2 to 15 wt%, and 3 to 15 wt%. When the total amount of ethylene and butene in the propylene-based copolymer is within the above range, when foamed beads are molded in a mold, the beads have good moldability under low molding pressure conditions, and molded articles with good mechanical properties such as compressive strength can be obtained. The amounts of ethylene and additional components in each propylene-based copolymer can be determined, for example, by IR spectroscopy. The propylene-based copolymer may be a linear propylene-based copolymer, a branched propylene-based copolymer, or a combination of both.

[0053] Examples of polyethylene-based resins include, but are not limited to, polyethylene homopolymers and ethylene-based copolymers containing more than 50% by mass of ethylene monomer. Polyethylene-based copolymers can be, or contain, random or block copolymers, with random copolymers being particularly preferred. Specifically, polyethylene-based resins include high-density polyethylene (HDPE), medium-density polyethylene (MDPE), low-density polyethylene (LDPE), linear low-density polyethylene (LLDPE), and linear ethylene copolymers such as ethylene-vinyl acetate (EVA) copolymers and ethylene methyl acrylate (EMA). Among these, LLDPE, a copolymer of ethylene and an α-olefin exhibiting a linear structure, is particularly preferred. Examples of suitable LLDPEs include ethylene-1-butene copolymers, ethylene-1-pentene copolymers, ethylene-1-hexene copolymers, ethylene-4-methyl-1-pentene copolymers, and ethylene-1-octene copolymers.

[0054] Polyamide-based resin refers to a polyamide homopolymer or polyamide copolymer. A polyamide homopolymer is based on one type of polyamide. A polyamide copolymer may be based on or contain, for example, a different type of polyamide resin. A polyamide copolymer refers to a copolymer having two or more repeating units, at least some of which have amide bonds. A polyamide copolymer can be a block copolymer containing a combination of a certain amount of the same amide repeating unit sequence and a certain amount of a different amide repeating unit sequence, or a random copolymer in which different amides are randomly repeated, with random copolymers being preferred. When the polyamide copolymer is a random copolymer, foam beads using the polyamide-based resin as a polymer material can be molded at a relatively low molding pressure.

[0055] Examples of polyamide homopolymers include, but are not limited to, poly(caprolactam) (nylon 6), poly(dodecalactam) (nylon 12), poly(hexamethylene adipamide) (nylon 66), poly(7-aminoheptanoic acid) (nylon 7), poly(8-aminooctanoic acid) (nylon 8), poly(9-aminononanoic acid) (nylon 9), poly(10-aminodecanoic acid) (nylon 10), and poly(11-aminoundecanoic acid). (Nylon 11), poly(hexamethylene sebacamide) (Nylon 610), poly(decamethylene sebacamide) (Nylon 1010), poly(hexamethylene azelamide) (Nylon 69), poly(tetramethylene adipamide) (Nylon 46), poly(tetramethylene sebacamide) (Nylon 410), poly(pentamethylene adipamide) (Nylon 56), and poly(pentamethylene sebacamide) (Nylon 510).

[0056] Examples of polyamide copolymers include polycaproamide / polyhexamethylene adipamide copolymer (nylon 6 / 66), caprolactam / hexamethylenediaminoadipic acid / lauryllactam copolymer (nylon 6 / 66 / 12), and caprolactam / lauryllactam copolymer (nylon 6 / 12). Among polyamide resins, polyamide resins consisting of one or a combination of two or more selected from the group consisting of nylon 6, nylon 66, nylon 6 / 66, and nylon 6 / 66 / 12 are preferred, with nylon 6 / 66 or nylon 6 / 66 / 12 being particularly preferred.

[0057] The melt mass flow rate (MFR) of a polypropylene-based resin can be measured under conditions of a temperature of 230°C and a load of 2.16 kg, and the value is preferably 3 g / 10 min or more, particularly 4 g / 10 min or more. When the MFR of a polypropylene-based resin falls within this range, the first-stage expanded resin particles in the pre-expansion step usually exhibit good expandability (expandability), and the expanded beads during molding usually exhibit good secondary expandability (expandability). Furthermore, the MFR of a polypropylene-based resin is preferably 15 g / 10 min or less, particularly 10 g / 10 min or less. When the MFR of a polypropylene-based resin falls within this range, the uniformity of the expanded beads and the physical properties of molded articles using the expanded beads can usually be improved. The MFR of a polypropylene-based resin is preferably 3 to 15 g / 10 min, more preferably 4 to 10 g / 10 min.

[0058] The melt mass flow rate (MFR) of the polyethylene resin can be measured under conditions of a temperature of 190°C and a load of 2.16 kg, and the value is preferably 0.5 g / 10 min or more, particularly 0.8 g / 10 min or more. When the MFR of the polyethylene resin falls within this range, the first-stage expanded resin particles in the pre-expansion step usually exhibit good expandability (expandability), and the expanded beads during molding usually exhibit good secondary expandability (expandability). Furthermore, the MFR of the polyethylene resin is preferably 4 g / 10 min or less, particularly 3 g / 10 min or less. When the MFR of the polyethylene resin falls within this range, the uniformity of the expanded beads and the physical properties of molded articles using the expanded beads can usually be improved. The MFR of the polyethylene resin is preferably 0.5 to 4 g / 10 min, more preferably 0.8 to 3 g / 10 min.

[0059] The MFR of a polypropylene-based resin or a polyethylene-based resin can be determined using the respective resin beads as test pieces in accordance with ISO 1133-1. The MFR can be measured, for example, using an MFR measuring device sold under the trade name "LMI4000" by Dynisco Corporation (38 Forge Parkway, Franklin MA 02038, USA).

[0060] The density of polypropylene resin is, for example, 0.80 to 0.95 g / cm ３ , 0.85-0.95g / cm ３ ,0.90~0.95g / cm ３ The density can be measured based on the method described in ISO 1183-3.

[0061] The density of the polyethylene resin is, for example, 0.80 to 0.96 g / cm ３ , 0.85-0.96g / cm ３ The density can be measured based on the method described in ISO 1183-3.

[0062] The density of the polyamide resin is preferably 1.05 g / cm ３ More preferably, 1.1 g / cm ３ The density can be measured based on the method described in ISO 1183-3.

[0063] When the polymer material of the foam beads is a polypropylene-based resin, the melting point of the polypropylene-based resin is preferably 130°C or higher, particularly 135°C or higher, and even more particularly 140°C or higher. When the melting point of the polypropylene-based resin is within this range, the mechanical properties such as compressive strength of the molded product obtained by molding the foam beads in a mold are usually good. Furthermore, the melting point of the polypropylene-based resin is preferably 155°C or lower, particularly 150°C or lower, and even more particularly 148°C or lower. When the melting point of the polypropylene-based resin is within this range, the molding process under low molding pressure conditions is usually good. That is, the melting point of the polypropylene-based resin is preferably 130°C to 155°C, more preferably 135°C to 150°C, and even more preferably 140°C to 148°C.

[0064] When the polymer material of the foam beads is a polyethylene-based resin, the melting point of the polyethylene-based resin is preferably 110°C or higher. When the melting point of the polyethylene-based resin is 110°C or higher, the resulting molded article is typically less likely to shrink and exhibits good shape recovery after molding. From the viewpoint of further improving moldability, the melting point of the polyethylene-based resin is preferably 112°C or higher, more preferably 115°C or higher. Furthermore, the melting point of the polyethylene-based resin is preferably 130°C or lower. When the melting point of the polyethylene-based resin is 130°C or lower, molding at low molding temperatures is typically facilitated, resulting in improved fusion properties and excellent moldability. From the viewpoint of further improving moldability, the melting point of the polyethylene-based resin is preferably 128°C or lower, more preferably 125°C or lower. That is, the melting point of the polyethylene-based resin is preferably 110°C to 130°C, more preferably 112°C to 128°C, and even more preferably 115°C to 125°C.

[0065] When the polymer material of the foam beads is a polyamide resin, the melting point of the polyamide resin is preferably 185°C or higher. When the melting point of the polyamide resin is 185°C or higher, the resulting molded article usually exhibits good heat resistance. From the viewpoint of further improving heat resistance, the melting point of the polyamide resin is preferably 188°C or higher, more preferably 190°C or higher. Furthermore, the melting point of the polyamide resin is preferably 280°C or lower. When the melting point of the polyamide resin is 280°C or lower, it is usually easy to control the process temperature during the primary expansion step, and processability is improved. From the viewpoint of further improving the processability of the polyamide resin, the melting point of the polyamide resin is preferably 260°C or lower, more preferably 240°C or lower. That is, the melting point of the polyamide resin is preferably 185°C to 280°C, more preferably 188°C to 260°C, and even more preferably 190°C to 240°C.

[0066] The melting point of any resin can be measured in accordance with Japanese Industrial Standard JIS K7122:2012 using a resin sample as a test specimen by the following procedure: Nitrogen is supplied to the resin sample at an inflow rate of 30 mL / min. The sample is heated from 23°C to 200°C at a heating rate of 10°C / min, held at that temperature for 10 minutes, cooled to 23°C at a cooling rate of 10°C / min, and heated again to 200°C at a heating rate of 10°C / min to obtain a differential scanning calorimetry (DSC curve) (DSC curve of the second heating). Next, the apex temperature of the melting peak in the DSC curve is determined, and this value is taken as the melting point of the resin. If multiple melting peaks appear in the DSC curve, the apex temperature of the melting peak with the highest melting peak height relative to the baseline is taken as the melting point. DSC measurements can be performed in accordance with Japanese Industrial Standard JIS K7122:2012.

[0067] Polyolefin resins and polyamide resins usually exhibit a flexural modulus of 100 MPa or more. From the viewpoint of improving the moldability of beads, the flexural modulus of polyolefin resins and polyamide resins is preferably less than 3000 MPa, more preferably less than 2000 MPa, and even more preferably less than 1500 MPa. The flexural modulus is determined based on Japanese Industrial Standard JIS K7171:2008.

[0068] The foam beads of the present disclosure may contain other polymer materials (hereinafter referred to as "other polymer materials") other than the polyolefin-based resins and polyamide-based resins described above, as long as the objects and effects of the present disclosure are not impaired. The other polymer materials are preferably other thermoplastic polymers (hereinafter referred to as "other thermoplastic polymers") other than the polyolefin-based resins and polyamide-based resins described above, or contain other thermoplastic polymers. More specifically, other thermoplastic polymers include polystyrene-based resins, polyester-based resins, polycarbonate-based resins, and modified polyphenylene ether-based resins. Examples of other polymer materials include thermoplastic elastomers such as olefin-based thermoplastic elastomers (TPOs) and urethane-based thermoplastic elastomers (TPUs). The other polymer materials may be used alone or in combination with at least two other materials.

[0069] The content of other thermoplastic polymers in the polymer material is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, and particularly preferably 0% by weight. That is, it is particularly preferable that the foamed beads contain substantially only polyolefin-based resin or polyamide-based resin as the thermoplastic polymer.

[0070] When a non-thermoplastic polymer is contained as the polymer material of the foamed beads, the content of the non-thermoplastic polymer is preferably 20% by weight or less, more preferably 10% by weight or less, even more preferably 5% by weight or less, and particularly preferably 0% by weight. That is, when a polymer other than a polyolefin-based resin and a polyamide-based resin is contained as the polymer material of the foamed beads, the other polymer is preferably a thermoplastic polymer other than the above-mentioned polyolefin-based resin and polyamide-based resin.

[0071] The foamed beads have a foamed layer and may further include at least one other layer on the foamed layer. Such beads can be considered multilayer beads including a foamed layer as a core layer and at least one other layer coating or covering the core layer. The at least one other layer may also be a resin layer, particularly a layer formed from a polyolefin-based resin or a polyamide-based resin. The at least one other layer may be formed by graft polymerizing a chemical substance such as a styrene monomer onto another layer such as the core layer, and then polymerizing the grafted chemical substance as needed to obtain multilayer beads. At least one of the core layer and the at least one other layer may include an opening, such as a through-hole.

[0072] In multilayer beads, at least one other layer may cover a portion or the entire outer surface of the foamed layer. When at least one other layer is a layer formed from a polyolefin-based resin or a layer formed from a polyamide-based resin, it is preferable that the melting point of the resin component contained in at least one other layer is lower than the melting point of the resin component contained in the foamed layer. This improves the fusion properties of the beads during molding. It is also preferable that at least one other layer is a substantially non-foamed resin layer. In this case, a molded product having good mechanical strength can usually be provided.

[0073] In multilayer beads, the ratio by weight of the components of the foamed layer to the components of the at least one other layer is preferably from 99:1 to 70:30 (foamed layer:at least one other layer), more preferably from 98:2 to 80:20, more preferably from 97:3 to 85:15.

[0074] As described above, each bead includes an outer shell or wall and closed cells within the outer shell or wall. Therefore, the closed cells of each bead are usually defined by the outer and / or inner wall elements of each bead, and the outer and / or inner wall elements partition the interior of the bead so that the closed cells within the foamed bead do not communicate with each other.

[0075] In another embodiment, the closed cells of the expanded beads may contain an inorganic gas or an inorganic gas mixture. Examples of inorganic gases include nitrogen and carbon dioxide. Examples of inorganic gas mixtures include air and a mixture of at least two of the aforementioned inorganic gases. The inorganic gas or inorganic gas mixture may be a blowing agent that enables further expansion of the first-stage expanded resin particles in the pre-expansion step, or may contain such a blowing agent. However, it is not preferred that the closed cells of the expanded beads contain organic gases, including pentane. For example, pentane is generally considered unsustainable, and has drawbacks, particularly high volatile organic compound (VOC) emissions and a high global warming potential (GWP).

[0076] In another embodiment, the ratio of the volume of closed cells to the volume of the expanded beads (closed cell ratio) is preferably at least 80%, particularly at least 83%, particularly at least 85%, particularly at least 87%, particularly at least 90%, particularly at least 93%, and particularly at least 95%. If the closed cell ratio is less than 80%, the recovery properties of a molded article produced under compression using the expanded beads may be reduced. Furthermore, the moldability of the beads may be reduced, and bubbles may form on the surface of a molded article produced from the beads. The closed cell ratio typically represents the ratio of the volume of closed cells to the total volume of the expanded beads, and can be determined, for example, using an air comparison hydrometer in accordance with ASTM D2856-70.

[0077] In another embodiment, the average particle size of the expanded beads can be, for example, 0.3 to 15 mm, particularly 0.5 to 10 mm, and more particularly 1 to 8 mm. The average particle size of the beads can be determined by the following method: first, based on the volume-based particle size distribution of the expanded beads, the beads are assumed to be spherical and converted to a number-based particle size distribution to obtain the number-based particle size distribution of the beads. Next, the particle sizes based on this particle size distribution are arithmetically averaged to obtain the number-based arithmetic mean particle size of the beads. The particle size refers to the diameter of a hypothetical sphere having the same volume as the beads. The volume-based particle size distribution of the expanded beads can be measured, for example, using a particle size distribution analyzer (e.g., Microtrac PartAn 3D, sold by Microtrac Bell Co., Ltd.). The number of beads used in the measurement is, for example, 2,000 or more.

[0078] The average mass per foamed bead (determined from the masses of 200 randomly selected beads) is preferably 0.1 to 20 mg, more preferably 0.2 to 10 mg, even more preferably 0.3 to 5 mg, and particularly preferably 0.4 to 2 mg.

[0079] In another embodiment, the foamed beads may have one or more melting peaks (high-temperature peaks) on the high-temperature side of the melting peak inherent to the resin of the beads (resin-specific peak) in a DSC curve obtained by differential scanning calorimetry (DSC) measured in accordance with Japanese Industrial Standards JIS K7122:2012, and such a case is preferred.

[0080] In particular, these melting peaks can be obtained by the following method. Specifically, a DSC curve is obtained by heating 1 to 5 mg of foamed beads from 23°C to 200°C at a heating rate of 10°C / min using a differential scanning calorimeter. The peak with the highest heat of fusion is the melting peak specific to the main resin of the beads, or the resin-specific peak, and one or more melting peaks that appear at higher temperatures are one or more high-temperature peaks. The DSC curve refers to the curve obtained by heating the beads using the above measurement method (the DSC curve of the first heating). The resin-specific peak refers to an endothermic peak resulting from the melting of crystals specific to the main resin that constitutes the foamed beads. In other words, the resin-specific peak is considered to be an endothermic peak that appears due to the endothermic heat caused by the melting of crystals that the resin that constitutes the beads normally has.

[0081] The following method can be used to identify peaks corresponding to the resin-specific peak or one or more high-temperature peaks: the foamed beads are heated from 23°C to 200°C at a heating rate of 10°C / min (first heating), then further cooled from 200°C to 23°C at a cooling rate of 10°C / min, and heated again from 23°C to 200°C at a heating rate of 10°C / min (second heating). In the DSC curve obtained in the second heating, only an endothermic peak due to the melting of crystals specific to the resin contained in the beads appears. This resin-specific peak appears in both the DSC curve from the first heating and the DSC curve from the second heating, and although the peak apex temperatures may differ slightly between the first and second heatings (usually the difference is less than 5°C), it is possible to identify which peak is the resin-specific peak. On the other hand, one or more endothermic peaks (high-temperature peaks) on the high-temperature side of the resin-specific peak are one or more endothermic peaks that appear above the resin-specific peak on the high-temperature side of the DSC curve from the first heating.

[0082] The heat of fusion of one or more high-temperature peaks of the expanded beads is preferably in the range of 5 to 40 J / g, more preferably 6 to 30 J / g, and even more preferably 7 to 25 J / g. When the heat of fusion of one or more high-temperature peaks of the beads is within the above range, a good part can usually be obtained by molding with a wider processing window. The heat of fusion of one or more high-temperature peaks can be measured as follows: On the DSC curve of the first heating, a straight line (α-β) is drawn connecting point α, which corresponds to 80°C on the DSC curve, and point β, which corresponds to the end temperature T of the melting of the beads. The end temperature T of the melting is the end point of the high-temperature peak on the high-temperature side, or the end point of the highest high-temperature peak if multiple high-temperature peaks are present, and is the intersection point of the high-temperature peak or, if multiple high-temperature peaks are present, the highest high-temperature peak with the baseline. Next, a straight line parallel to the vertical axis of the graph is drawn from point γ on the DSC curve. This point corresponds to the point with the lowest heat in the valley between the resin-specific peak and the high-temperature peak, or, if multiple high-temperature peaks are present, the point of the lowest high-temperature peak. The intersection point with the above line (α-β) is designated as δ. The heat of fusion of one or more high-temperature peaks corresponds to the value obtained by dividing the area of ​​one or more high-temperature peaks enclosed by the curve of one or more high-temperature peaks in the DSC curve, the line segment (δ-β), and the line segment (γ-δ) by the mass of the beads used in the experiment, and is expressed in J / g.

[0083] A second aspect of the present disclosure is a method for producing expanded beads having a cellular structure, the expanded beads having a spherical shape defined by a sphericity φ of greater than 0.94 and less than 1.00, and an angle of repose of 31.0° to 50.0° measured in accordance with ISO 4324.

[0084] As described above, expanded beads are usually obtained through a primary expansion step. In particular, the primary expansion step may include a step of applying temperature and / or pressure to a dispersion medium, particularly an aqueous dispersion medium, containing raw material beads (hereinafter referred to as "resin particles") for a specific period of time, for example, in an autoclave process or an extrusion foaming process, to expand the resin particles to a certain extent.

[0085] The resin particles include a polymer material. Examples of the polymer material include the polyolefin-based resin or polyamide-based resin described in the first embodiment of the present disclosure. The resin particles may further include at least one additive. Examples of the at least one additive include the cell nucleation additive, flame retardant additive, thermal conductive additive, conductive additive, magnetic additive, and light absorbing additive described in the first embodiment of the present disclosure.

[0086] An example of the primary expansion process is an autoclave process in which resin particles containing a polymer material are dispersed in a dispersion medium such as water. After the resin particles are impregnated with a blowing agent such as carbon dioxide, the resin particles containing the blowing agent are discharged together with the dispersion medium under low pressure.

[0087] For example, resin particles can be produced by a strand cutting method. First, a polymer material and additives such as a light-absorbing additive and a nucleating agent are fed into an extruder as needed, and the mixture is heated and kneaded to form a resin melt. The resin melt is then extruded through small holes in a die attached to the tip of the extruder to form strands. After cooling, the extrudate is cut to the desired length to obtain resin particles. The method for producing resin particles is not limited to the above-mentioned method, and other methods such as a hot cutting method and an underwater cutting method can also be used.

[0088] In the autoclave process, the shape of the first-stage expanded resin particles obtained in the primary expansion process is an image of the shape of the resin particles. For example, in order to obtain first-stage expanded resin particles having high sphericity in the primary expansion process, cylindrical resin particles are usually used.

[0089] As described above, the resin particles are dispersed in a dispersion medium. The operation of dispersing the resin particles in the dispersion medium can be performed in a sealed container. As the dispersion medium, for example, an aqueous dispersion medium containing water as a main component can be used. The aqueous dispersion medium may contain, in addition to water, a hydrophilic organic solvent such as ethylene glycol, glycerin, methanol, or ethanol. The proportion of water in the aqueous dispersion medium is preferably 60% by mass or more, more preferably 70% by mass or more, and even more preferably 80% by mass or more.

[0090] In the foaming process, a dispersant is preferably added to the dispersion medium to suppress fusion between resin particles heated in a container. The amount of dispersant added is preferably 0.001 parts by mass or more and 5 parts by mass or less per 100 parts by mass of resin particles. Organic or inorganic dispersants can be used, but particulate inorganic materials are preferred as dispersants due to ease of handling. More specifically, examples of dispersants include clay minerals such as kaolin, mica, and clay, aluminum oxide, titanium oxide, basic magnesium carbonate, basic zinc carbonate, calcium carbonate, and iron oxide. These dispersants may be used alone or in combination. Among these, clay minerals are preferably used as dispersants.

[0091] When a dispersant is used, it is preferable to use an anionic surfactant such as sodium dodecylbenzenesulfonate, sodium alkylbenzenesulfonate, sodium lauryl sulfate, or sodium oleate in combination as a dispersing aid. The amount of the dispersing aid added is preferably 0.001 part by mass or more and 1 part by mass or less per 100 parts by mass of the resin particles.

[0092] After dispersing the resin particles in a dispersion medium, the resin particles are impregnated with a blowing agent. The blowing agent impregnated into the resin particles is preferably a physical blowing agent. Examples of physical blowing agents include inorganic physical blowing agents such as carbon dioxide, air, nitrogen, helium, and argon. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, and hexane; alicyclic hydrocarbons such as cyclopentane and cyclohexane; and halogenated hydrocarbons such as fluoromethane, trifluoromethane, 1,1-difluoromethane, 1-chloro-1,1-dichloroethane, 1,2,2,2-tetrafluoroethane, methyl chloride, ethyl chloride, and methylene chloride. These physical blowing agents may be used alone or in combination. Furthermore, a mixture of at least one inorganic physical blowing agent and at least one organic physical blowing agent may be used. From the standpoints of safety and environmental sustainability, inorganic physical blowing agents are preferred, with carbon dioxide being particularly preferred.

[0093] The amount of the foaming agent added relative to 100 parts by mass of the resin particles is preferably 0.1 parts by mass or more and 30 parts by mass or less, and more preferably 0.5 parts by mass or more and 15 parts by mass or less.

[0094] The impregnation of the blowing agent can be carried out in a sealed container, and the pressure inside the sealed container can be increased to impregnate the resin particles in the dispersion medium with the blowing agent. The impregnation is preferably carried out under the influence of temperature, because high temperatures further promote the impregnation of the resin particles with the blowing agent.

[0095] The pressure in the sealed container during expansion is preferably 0.5 MPa (G) or more, and preferably 4.0 MPa (G) or less, in terms of gauge pressure. Within the above range, first-stage expanded resin particles can be produced safely without damaging the sealed container.

[0096] After the impregnation step is completed, the resulting resin particles are released into an environment with a lower pressure than that in the pressurization step. As a result, the resin particles expand, forming closed cells inside, resulting in first-stage expanded resin particles. The degree of expansion of the first-stage expanded resin particles is further increased by treating the beads in a pre-expansion step, as explained below. An increase in the degree of expansion is associated with a decrease in the respective densities, and beads that have undergone the pre-expansion step have a lower density than beads that have undergone only the primary expansion step. The expansion ratio between the primary expansion step and the pre-expansion step indicates the ratio of the bulk density of the expanded beads to the bulk density of the first-stage expanded resin particles. The expansion ratio between the primary expansion step and the pre-expansion step is calculated by multiplying the bulk density [kg / m] of the beads before treatment in the pre-expansion step. ３ ] (usually the bulk density of the first-stage expanded resin particles) is calculated by multiplying the bulk density of the expanded beads [kg / m ３ The angle of repose and sphericity can also be adjusted by controlling the expansion ratio between the primary expansion step and the pre-expansion step. The expansion ratio between the primary expansion step and the pre-expansion step is preferably 2.0 to 4.0, and more preferably 2.1 to 3.8.

[0097] A method for producing expanded beads having a cellular structure includes at least the following steps: a first step is to supply first-stage expanded resin particles having a cellular structure onto a conveying device such as a conveyor belt. The first-stage expanded resin particles have a first angle of repose and include a polymer material and at least one additive. A second step is to move the conveying device relative to at least one heating device. The heating device applies thermal energy to the first-stage expanded resin particles by radiating infrared rays. Here, the at least one additive exhibits a higher absorption rate of infrared rays than the polymer material. The at least one additive produces expanded beads having a cellular structure. The expanded beads have a spherical shape defined by a sphericity φ of greater than 0.94 and less than 1.00, and an angle of repose of 31.0° to 50.0° measured in accordance with ISO 4324. The second step typically involves expanding the first-stage expanded resin particles to produce expanded beads having a spherical shape, as defined by a sphericity φ of greater than 0.94 and less than 1.00, and the expanded beads have an angle of repose of 31.0° to 50.0° measured in accordance with ISO 4324.

[0098] The first-stage expanded resin particles provided in the first step of the present method have a higher density than the expanded beads produced in the second step of the present method. That is, the method of the second aspect of the present disclosure is used to produce the expanded beads of the first aspect of the present disclosure. The density of the first-stage expanded resin particles is preferably 30 kg / m ３ Above, 120kg / m ３ The range can be as follows:

[0099] The first angle of repose of the first-stage expanded resin particles measured in accordance with ISO 4324 is, for example, 15.5° to 43.5°. The lower limit of the first angle of repose is, in order of preference, 15.5°, 16.0°, 16.5°, 17.0°, 17.5°, 18.0°, 18.5°, 19.0°, 19.5°, 20.0°, 20.5°, 21.0°, 21.5°, 22.0°, 22.5°, 23.0°, 23.5°, 24.0°, 24.5°, and 25.0°. The upper limit of the first angle of repose is, in order of preference, 43.5°, 43.0°, 42.5°, 42.0°, 41.5°, 41.0°, 40.5°, 40.0°, 39.5°, 39.0°, 38.5°, 38.0°, 37.5°, 37.0°, 36.5°, 36.0°, 35.5°, 35.0°, 34.5°, 34.0°, 33.5°, 33.0°, 32.5°, 32.0°, 31.5°, 31.0°, 30.5°, 30.0°, and 29.5°. Therefore, the range of the first angle of repose is, for example, 15.5° to 43.5°, 16.0° to 43.0°, 16.5° to 42.5°, 17.0° to 42.0°, 17.5° to 41.5°, 18.0° to 41.0°, 18.5° to 40.5°, 19.0° to 40.0°, 19.5° to 39.5°, 20.0° to 42.0 ... ° to 39.0°, 20.5° to 38.5°, 21.0° to 38.0°, 21.5° to 37.5°, 22.0° to 37.0°, 22.5° to 36.5°, 23.0° to 36.0°, 23.5° to 35.5°, 24.0° to 35.0°, 24.5° to 34.5°, 25.0° to 34.0°.

[0100] The lower limit of the content of the at least one light-absorbing additive in the first-stage expanded resin particles is, for example, 0.1 wt%, 0.2 wt%, 0.3 wt%, 0.4 wt%, 0.5 wt%, 0.6 wt%, 0.7 wt%, 0.8 wt%, 0.9 wt%, 1.0 wt%, 1.5 wt%, 2.0 wt%, 2.5 wt%, 3.0 wt%, 3.5 wt%, 4.0 wt%, 4.5 wt%, or 5.0 wt%, and the upper limit of the content of the at least one light-absorbing additive in the first-stage expanded resin particles is, for example, 20.0 wt%, 15 wt%, 10.0 wt%, 9.5 wt%, 9.0 wt%, 8.5 wt%, 8.0 wt%, 7.5 wt%, 7.0 wt%, 6.5 wt%, or 6.0 wt%. Thus, the content of the at least one light absorbing additive may be, for example, 0.1 wt % to 10.0 wt %, 0.2 wt % to 9.5 wt %, 0.3 wt % to 9.0 wt %, 0.4 wt % to 8.5 wt %, 0.5 wt % to 8.0 wt %, 0.6 wt % to 7.5 wt %, 0.7 wt % to 7.0 wt %, 0.8 wt % to 6.5 wt %, 0.9 wt % to 6.0 wt %, 1.0 wt % to 6.0 wt %, 1.5 wt % to 6.0 wt %, or 2.0 wt % to 6.0 wt %.

[0101] The at least one light absorbing additive may comprise one or more organic and / or inorganic pigments (dyes), and thus may typically be or comprise a pigment configured to absorb infrared radiation (as previously mentioned, typically a wavelength range comprising wavelengths from 750 nm to 8 μm, particularly 1 μm to 4 μm).

[0102] Examples of inorganic pigments include chromates such as lead chromate (yellow), zinc chromate (yellow), and barium chromate (yellow), ferrocyanides such as Prussian blue (dark blue), sulfides such as cadmium sulfide (yellow) and cadmium sulfide selenide (red), oxides such as iron oxide (red, yellow, and brown) and titanium dioxide (white), and silicates such as ultramarine blue. Examples of organic pigments include azo pigments such as monoazo pigments, diazo pigments, azo lakes, and condensed azo pigments, and polycyclic pigments such as phthalocyanines (blue and green), anthraquinones (red), perylenes (red), perinones (orange), thioindigo (purple), quinacridones (red), dioxazines (purple), isoindolinones (yellow), and quinophthalones (yellow).

[0103] In another embodiment, the at least one light absorbing additive may be or include a black inorganic pigment comprising carbon particles, such as one or more materials selected from carbon black, conductive carbon, graphene, graphite, and carbon nanostructures, such as tubes, layers, and the like.

[0104] According to specific embodiments, the at least one light absorbing additive is or includes carbon black, examples of which include, but are not limited to, channel black, roller black, furnace black, thermal black, acetylene black, and ketjen black.

[0105] Other exemplary light absorbing additives that are not pigments are also contemplated, such as specialized near-infrared absorbers, including, but not limited to, metal oxides and sulfides such as tungsten oxide, tin oxide, antimony oxide, lead sulfide, and the like, or mixtures and / or compounds thereof.

[0106] In the second step of the method, the first-stage expanded resin particles can be moved by (actively) moving a conveying device relative to a stationary heating device, by (actively) moving the heating device relative to a stationary conveying device, or by (actively) moving the conveying device and the heating device relative to each other. In either case, one or more driving devices, such as drive motors, can be assigned to the conveying device and / or the heating device. The heating device can include one or more heating structures, which can be configured to emit light of a specific wavelength or range of wavelengths. Specific examples of heating structures include infrared emitting structures configured to emit light of wavelengths in the range of 750 nm to 8 μm, particularly 1 μm to 4 μm.

[0107] The conveying device may include a support surface for supporting the first-stage expanded resin particles. The support surface may have a three-dimensional structure, for example, including ridges and / or depressions, and preferably includes a receiving portion shaped and sized to receive one or more first-stage expanded resin particles.

[0108] The first-stage expanded resin particles are irradiated with infrared light. When the first-stage expanded resin particles contain at least one additive that exhibits a higher infrared absorption rate than the polymer material, and the first-stage expanded resin particles are placed and supported on a (substantially) planar structure, such as a conveying device, heat transfer by infrared light irradiation is believed to be improved compared to conventional processes in which the first-stage expanded resin particles do not contain, or do not contain enough of, the additive that exhibits a higher infrared absorption rate than the polymer material. At least a portion of the irradiated infrared light is absorbed by the additive, but the additive is believed to prevent the infrared light from passing through the substantially translucent polymer, or at least reduce the radiation level passing through the substantially translucent polymer. Because the first-stage expanded resin particles are supported on a (substantially) planar surface, heat transfer occurs anisotropically, and one or more flat portions are formed in the produced beads at the portions of the contact surface between the support surface and the first-stage expanded resin particles where the radiation level is lowest.

[0109] According to one embodiment of the present method, the ratio of the angle of repose of the expanded beads to the first angle of repose of the first-stage expanded resin particles (the value obtained by dividing the angle of repose of the expanded beads by the first angle of repose of the first-stage expanded resin particles) can be in the range of 1.15 to 2.00. In particular, the ratio of the angle of repose of the expanded beads to the first angle of repose of the first-stage expanded resin particles can be in the range of 1.18 to 1.80, and even more preferably 1.20 to 1.60. Thus, the present method can increase the angle of repose of the beads by at least 15%, even more preferably at least 18%, and even more preferably at least 20%. This is believed to be due to the fact that the first-stage expanded resin particles are placed on the support surface of the conveying device and irradiated with infrared rays while being supported by the support surface, causing the first-stage expanded resin particles to expand.

[0110] In another embodiment of the method, the at least one heating device may be a radiant heating device including multiple radiant elements, such as infrared emitters, configured to irradiate the first-stage expanded resin particles with infrared radiation. Thus, the at least one heating device may be or include an infrared oven, or may include one or more infrared emitters arranged or formed along the corresponding conveyor path. The infrared emitters may have variable radiant power, as desired, for example, in the range of 0.1 to 500 kW, particularly in the range of 0.5 to 250 kW, particularly in the range of 0.5 to 50 kW, and particularly in the range of 1 to 10 kW. Any and all intermediate values ​​not explicitly recited herein are also included. Variable radiant or variable radiant (area) power can be used to create different temperature zones, thereby providing parameters for influencing the expansion process.

[0111] The method can be carried out according to the principles disclosed in WO 2022 / 229286 A1, the contents of which are incorporated herein by reference. Thus, the method can comprise the steps of providing a raw material containing foamed beads having a cellular structure, adding a blowing agent to the beads under at least the influence of pressure, and expanding the foaming agent-containing beads under the influence of temperature. The expansion of the foaming agent-containing beads under the influence of temperature is carried out by irradiating the foaming agent-containing beads with high-energy thermal radiation, in particular infrared radiation. Gases such as carbon dioxide or mixtures containing carbon dioxide and / or nitrogen, e.g., air, can be used as the foaming agent.

[0112] In another embodiment of the method, the transport device may be a conveyor belt having a desired moving speed. In particular, the moving speed of the conveyor belt can be selected based on, for example, the distance over which the first-stage expanded resin particles are irradiated and the length of the at least one heating device. The appropriate time for exposing the first-stage expanded resin particles to radiation can be determined taking into account the radiation output of one or more infrared emitters and the desired properties of the resulting beads. In other words, the energy supplied to the first-stage expanded resin particles can be adjusted by adjusting the moving speed of the conveyor belt and thus the exposure time of the first-stage expanded resin particles to radiation, or by adjusting the radiation output of one or more infrared emitters. The energy (kJ) supplied to the first-stage expanded resin particles is defined as the product of the total radiation output (kW) of the one or more infrared emitters irradiating the first-stage expanded resin particles during the transport process multiplied by the exposure time (s) of the first-stage expanded resin particles to radiation.

[0113] To produce expanded beads having an angle of repose of 31.0° or more while shortening the pressurization step of the first-stage expanded resin beads containing a blowing agent, the energy supplied to the first-stage expanded resin beads can be preferably 10 kJ or more, 15 kJ or more, 17 kJ or more, or 20 kJ or more. To produce beads having high sphericity, the energy (kJ) supplied to the first-stage expanded resin beads can be preferably 50 kJ or less, 45 kJ or less, 40 kJ or less, or 35 kJ or less. The energy supplied to the first-stage expanded resin beads can be, for example, in the range of 10 kJ to 50 kJ, 12 to 45 kJ, 15 to 40 kJ, or 20 to 35 kJ.

[0114] In another embodiment of the present method, the expansion ratio, obtained by dividing the density of the first-stage expanded resin particles by the density of the expanded beads, is 1.5 to 5.0. When the expansion ratio is higher than 1.5, particularly higher than 1.8, particularly higher than 2.0, and particularly higher than 2.5, it is usually easier to obtain beads having an angle of repose of 31.0° or more. When the expansion ratio is lower than 5.0, particularly lower than 4.5, and particularly lower than 4.0, it is usually easier to obtain expanded beads having a very good spherical shape with a sphericity of more than 0.94.

[0115] A third aspect of the present disclosure is a collection of particulate polymeric materials comprising expanded beads according to the first aspect of the present disclosure, which can thus form part of a composite material, which can have a wide range of applications.

[0116] A fourth aspect of the present disclosure is a method for producing a molded article, the method comprising the steps of: providing foamed beads to a mold cavity; and molding the foamed beads to produce a molded article. The molding step may include injecting heat energy, e.g., via steam, into the cavity to bond the beads and form the molded article.

[0117] In the method for manufacturing a molded product by processing foamed beads by molding according to the first aspect of the present disclosure, the beads are filled into a molding die and then heated to produce a molded product. Specifically, after filling the molding die with the beads, the beads are heated to cause secondary expansion and to fuse the beads together, thereby obtaining a part having the shape of the molding space. Examples of methods for heating the foamed beads include a method in which a heating medium such as steam is introduced into the molding die to heat the beads with the heating medium, a method in which the beads are irradiated with electromagnetic waves such as high frequency waves, a method in which the beads are bonded by introducing a specific chemical substance (ATECARMA), a method in which the molding die is conductively heated without introducing steam into the mold to fuse the beads within the molding die, and a combination of these methods.

[0118] The method for filling the foamed beads into a molding die can be a known method. For example, there is a method in which the beads are directly pressed into a pressure die with pressurized gas and then the pressure inside the die is released (pressure filling method), or a method in which the die is opened in advance to expand the molding space, and then the beads are filled into the die, and the die is closed after filling, thereby mechanically compressing the beads (cracking filling method). Before filling, if necessary, the beads can be pressurized with a gas such as air to apply a predetermined internal pressure to the bubbles in the beads, thereby imparting a certain degree of additional foaming ability to the beads.

[0119] The molded article thus produced from the foam beads according to the first aspect of the present disclosure by the manufacturing method according to the fourth aspect of the present disclosure can be, for example, a technical part or form part of a technical part. For example, such a molded article can be a part of a vehicle, in particular a part to be placed in a vehicle such as an automobile, aircraft, ship, etc. More specific molded articles include, but are not limited to, case elements, housing elements, protective elements, etc. for battery devices, electrical devices, electronic devices, etc.

[0120] It should be noted that all statements relating to the expanded beads according to the first aspect of the present disclosure also apply to the method according to the second aspect of the present disclosure, and vice versa, and / or to the particulate polymer material aggregate according to the third aspect of the present disclosure, and vice versa, and / or to the method for producing a molded article according to the fourth aspect of the present disclosure, and vice versa.

[0121] Furthermore, one embodiment of the present disclosure will be described more specifically below with reference to the drawings.

[0122] Figures 1 and 2 are diagrams of beads of one embodiment, and Figure 3 is a typical DSC curve for measuring high temperature peak area of ​​one embodiment.

[0123] The beads 10 shown in Fig. 1 are foamed beads having a cellular structure made of a polyolefin resin (e.g., a polypropylene resin) or a polyamide resin. The density of the beads 10 is, for example, 12 to 40 kg / m ３ is.

[0124] The beads 10 comprise a polymeric material and at least one additive, the at least one additive exhibiting a higher absorption rate than the polymeric material in the infrared wavelength range, particularly in the wavelength range including wavelengths from 750 nm to 8 μm, and particularly from 1 μm to 4 μm. The at least one additive may be a pigment such as carbon black, and the beads 10 may comprise the additive in an amount of, for example, 0.1 to 10% by weight.

[0125] As is clear from FIG. 1 , the foamed beads have at least one flat portion 11 and sidewall portions 12, 13. As is further clear from FIG. 1 , the angle α between the at least one flat portion 11 and the sidewall portions 12, 13 can be an angle in the range of 90° to 160°. When the flat portion 11 of the bead is taken as the bottom surface of the bead, the at least one flat portion 11 of the bead 10 may have a length 11e corresponding to 40 to 60% of the parallel diameter D of the bead 10, which corresponds to the length of a line segment formed by the intersection of the periphery of the cross section of the bead 10 with a line passing through the center of the cross section and parallel to the two parallel lines that are the smallest distance between the flat portion of the bead 10 and sandwiching the flat portion of the bead 10, in a cross section perpendicular to the two parallel planes that pass through the center of the bead 10 and sandwich the bottom surface at the smallest distance. The center of the bead here refers to the center of gravity of the bead, and the center of the cross section refers to the center of gravity of the cross section of the bead.

[0126] As is further apparent from Figure 1, beads 10 contain closed cells 14 that contain an inorganic gas or mixture of inorganic gases. Notably, at least 80% of the volume of beads 10 are closed cells 14. Beads 10 have a spherical shape, defined by a sphericity φ greater than 0.94 and less than 1.00, and an angle of repose of 31.0° to 50.0° as measured in accordance with ISO 4324.

[0127] FIG. 2 is a principle diagram, not to scale, of an exemplary embodiment of a method for producing expanded beads having a cellular structure and beads 10 produced by the exemplary embodiment of the method.

[0128] This embodiment includes at least the following steps: (1) supplying first-stage expanded resin particles having a cellular structure onto a conveying device 20 such as a conveyor belt; and (2) moving the conveying device 20 relative to at least one heating device 30 (e.g., an infrared radiation device) as shown by arrow A1.

[0129] The heating device 30 applies thermal energy, particularly by radiating infrared rays, to the first-stage expanded resin particles to produce expanded beads 10 having a cellular structure. The polymer beads 10 have a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and an angle of repose of 31.0° to 50.0° measured in accordance with ISO 4324.

[0130] Figure 2 shows beads 10 at the end of a conveying device 20, i.e., beads 10 that have (essentially) undergone pre-expansion by infrared irradiation in a so-called pre-expansion step, i.e., beads 10 that have been produced according to the production method described above.

[0131] FIG. 3 shows a typical DSC curve for measuring the area of ​​the high temperature peak according to one embodiment for beads made of polypropylene resin as the polymer material.

[0132] In Tables 1 and 2 shown below, seven examples of beads according to the first aspect of the present disclosure (Table 1) and six comparative examples (Table 2) are shown in the row labeled "expanded beads." As is clear from Table 1, the beads of all the examples have a sphericity of more than 0.94 and less than 1.00, and an angle of repose measured in accordance with ISO 4324 of 31.0° or more and 50.0° or less, particularly 31.5° or more.

[0133] The angle of repose was measured using a repose angle measuring device (product number L50566070) in accordance with ISO 4324. The measuring device is commercially available from Landgraf Laborsysteme HLL (magdeburger Strasse 3, 30855 Langenhagen; Germany) (see URL: https: / / www.hallflowmeter.de / 12 / 158 / AD223 / TDUwNTY2MDcw / 223-L50566070-landgrafhll.html?sid=c69jj62j69pkptk4asdegi3s37). To prevent adverse effects of static electricity during measurement, the device was grounded, and excess static electricity remaining on the surface of the foamed beads was removed as needed using an ion gun, such as one sold under the trade name 8193 GEN4 Ion Air Gun by EXAIR, Inc. (11510 Goldcoast Drive, Cincinnati, Ohio 45249-1621, USA).

[0134] The sphericity of the expanded beads was measured using a particle size distribution analyzer (Microtrac PartAn 3D; Microtrac Bell Co., Ltd.; Japan). The number of beads used for the measurement was 2,000 or more.

[0135] The row labeled "First-stage expanded resin particles" in each table shows the basic parameters of each first-stage expanded resin particle. As described above, the primary expansion step is a step in which resin particles, particularly compressed resin particles, are first expanded under the influence of temperature and / or pressure.

[0136] Example 1 An extruder with an inner diameter of 50 mm and a circular die for forming strands was prepared. A polypropylene resin (ethylene-propylene copolymer (referred to as "PP" in the table) having a melting point of 143°C, an ethylene content of 2.1 wt%, and an MFR of 6 g / 10 min (measured in accordance with ISO 1133-1 at 230°C and a load of 2.16 kg) was supplied to the extruder in a total amount of 100 wt%, along with 0.05 wt% zinc borate and 2.4 wt% carbon black (referred to as "CB" in the table) as a light-absorbing additive. The resulting resin melt was extruded as a strand from a strand-forming die attached to the tip of the extruder. The extruded strand was cooled in water and cut with a pelletizer to obtain resin particles (average mass per particle: 1 mg). Table 1 shows the polymer materials and light-absorbing additives used in the production of the resin particles.

[0137] Into a 100 L sealed container were placed 8 kg of the resin particles obtained above, 69 L of water as a dispersion medium, 77 g of kaolin as a dispersant, and 39 g of sodium dodecylbenzenesulfonate as a dispersing aid.

[0138] Next, carbon dioxide was pressurized to a gauge pressure of 0.5 MPa (G) as a blowing agent and filled into the sealed container. The contents of the sealed container were then heated to a foaming temperature of 153°C. Carbon dioxide was then pressurized to a pressure of 2.0 MPa (G) (foaming pressure) and filled into the sealed container, and the same temperature and pressure were maintained for 15 minutes. The contents of the sealed container were then released under atmospheric pressure, and the resin particles were expanded to obtain first-stage expanded resin particles. The density of the first-stage expanded resin particles and the angle of repose based on ISO 4324 were measured. The measurement results are shown in Table 1.

[0139] The primary expanded beads were left to mature for 24 hours in an environment of an air temperature of 23°C, a relative humidity of 50%, and 1 atmosphere. Next, the matured first-stage expanded resin beads were filled into a pressurized sealed container, and the pressure inside the sealed container was increased to pressurize the first-stage expanded resin beads. This pressurization step was carried out at a predetermined pressure of at least 0.1 MPa (G) for a predetermined time of at least 1 hour, allowing air to be impregnated into the cells of the first-stage expanded resin beads. Thereafter, the first-stage expanded resin beads were removed from the sealed container, and first-stage expanded resin beads having an internal cell pressure (ICP) shown in Table 1 were obtained.

[0140] The first-stage expanded resin particles were then placed on a conveyor belt that transported the beads while containing pressurized air, and passed through an infrared continuous oven equipped with several infrared emitters (referred to as the "IR" process in Tables 1 and 2) at an output of 30 kg / h to produce expanded beads. The total radiation output of the infrared emitters during the heating process, the exposure time of the first-stage expanded resin particles containing pressurized air (to infrared radiation) (equivalent to the length of time the first-stage expanded resin particles were irradiated divided by the speed of the conveyor belt), and the energy supplied to the first-stage expanded resin particles (defined as the product of the exposure time (s) of the first-stage expanded resin particles (to infrared radiation) and the total radiation output (kW) of the infrared emitters) were as shown in Table 1. The measurement results of the properties of the obtained expanded beads are shown in Table 1.

[0141] The shape of the foamed beads was observed at the flat surface. One of the obtained foamed beads was cut in half with a razor blade along a plane that passed through the center of the bead and was perpendicular to two parallel planes with the smallest distance between them, sandwiching the flat surface. The obtained half bead was observed with a microscope VHX-6000 sold by Keyence Corporation (1-3-14 Higashinakajima, Higashiyodogawa-ku, Osaka City, Osaka Prefecture, Japan 533-8555). The center of the bead referred to here is the center of gravity of the bead.

[0142] The angle α between the flat portion and the two sidewalls between which the flat portion extended was measured and found to be 124°. The length of the flat portion was 2117 μm. In the cross section of the obtained half bead, when the flat portion is taken as the bottom surface, the angle α was 47% of the parallel diameter of the bead, which corresponds to the length of the line segment formed by the intersection of a line passing through the center of the cross section and the periphery of the cross section of the bead in the cross section, which is parallel to two parallel lines with the smallest distance between them, when the flat portion is taken as the bottom surface. The center of the bead here refers to the center of gravity of the cross section.

[0143] Next, molding was performed using the obtained foamed beads. A split mold for molding a flat plate having a molding space of 400 mm length x 300 mm width x 30 mm thickness was prepared as a mold. The obtained foamed beads were directly filled into the molding space with compressed air, and the mold was closed. Next, steam was supplied into the mold to heat the foamed beads, and a plate-shaped molded product was formed.

[0144] Heating with steam was performed as follows. First, with drain valves on both sides of the mold open, steam was supplied into the mold (exhaust process). Next, with one drain valve open, steam was supplied into the mold from the other drain valve to heat the foamed beads (one-sided heating process). Next, with the other drain valve open, steam was supplied from one of the mold sides (reverse one-sided heating process). Then, with drain valves on both sides of the mold closed, steam was supplied from both sides until the molding steam pressure inside the mold reached 0.32 MPa (G) (two-sided heating process). After the two-sided heating process was completed, the pressure inside the mold was released, and the mold was cooled with water until the pressure (surface pressure) generated on the molding surface of the mold due to the expansion pressure of the foamed beads during the molding process reached 0.05 MPa (G).

[0145] The mold was then opened, and the foamed bead molded article was removed from the mold. The molded article removed from the mold was cured in an oven at 80°C for 12 hours and then slowly cooled to room temperature. The cycle time (seconds), which corresponds to the total molding time of the foamed beads in the mold, and the compression ratio, which corresponds to the ratio of the density of the molded article to the density of the foamed beads used to produce the molded article (density of molded article: density of foamed beads), are shown in Table 1.

[0146] (Examples 2 to 6) Expanded beads were obtained in the same manner as in Example 1, except that the content of the light-absorbing additive, the density of the first-stage expanded resin particles, and the processing parameters of the IR step were changed. The content of the light-absorbing additive, the measured density of the beads, and the related processing conditions are shown in Table 1.

[0147] (Example 7) Foamed beads were obtained in the same manner as in Example 1, except that a light-absorbing additive other than carbon black was used and the content of the light-absorbing additive, the density of the first-stage expanded resin particles, and the processing parameters of the IR step were changed. The content of the light-absorbing additive, the measured bead density, and the related processing conditions are shown in Table 1.

[0148] (Comparative Examples C1 to C6) First-stage expanded resin particles and expanded beads were obtained in the same manner as in Examples 1 to 6, except that instead of the IR step in the Examples, the first-stage expanded resin particles were pressurized in a pressurizable sealed container and then supplied to a steam pre-expansion machine (referred to as the "steam" step in Table 2) in which the pressurized first-stage expanded resin particles were heated with heated steam.

[0149] Comparative Example C7 First-stage expanded resin particles and expanded beads were obtained under almost the same production conditions as in Example 5, except that no light-absorbing additive was used.

[0150] In particular, by matching Examples 1 to 6 in Table 1 with Comparative Examples C1 to C6 in Table 2 and comparing the parameters shown in each table, it was confirmed that processing foamed beads according to the present disclosure can significantly shorten the molding cycle time. The foamed beads obtained in Comparative Example C7 had an angle of repose of 28.2°. The cycle time for obtaining a molded product from foamed beads in Comparative Example C7 was longer than that in Example 6, which used foamed beads with the same density and was molded at approximately the same compression ratio.

[0151]

[0152]

[0153] This application is based on European Patent Application EP 24315397.0 filed on August 29, 2024, the contents of which are incorporated herein by reference.

Claims

1. Expanded beads having a cellular structure, a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and an angle of repose measured in accordance with ISO 4324 of 31.0° to 50.0°.

2. 12-40kg / m ３ 10. The expanded beads of claim 1 having a bulk density of 3. The expanded beads according to claim 1 or 2, which have at least one flat surface.

4. Expanded beads according to any one of claims 1 to 3, comprising a polymeric material and at least one additive, said additive exhibiting a higher absorption rate of infrared radiation than said polymeric material.

5. The expanded beads according to claim 4, containing 0.1 to 10% by weight of said additive.

6. The foam beads of claim 4 or 5, wherein the additive comprises one or more organic and / or inorganic pigments.

7. The expanded beads according to any one of claims 4 to 6, wherein the additive is carbon black.

8. The foam beads according to any one of claims 4 to 7, wherein the polymer material is a polyolefin resin or a polyamide resin.

9. The expanded beads of any one of claims 1 to 8, wherein the cellular structure comprises closed cells, and the closed cells contain an inorganic gas or mixture of inorganic gases.

10. The expanded beads of claim 9, wherein the ratio of the volume of the closed cells to the volume of the expanded beads is at least 80%.

11. A method for producing foamed beads having a cellular structure, comprising the steps of: supplying pre-expanded first-stage expanded resin particles onto a conveying device; and moving the conveying device relative to at least one heating device, which applies thermal energy to the first-stage expanded resin particles by radiating infrared rays, thereby producing foamed beads having a cellular structure, wherein the foamed beads have a spherical shape defined by a sphericity φ of more than 0.94 and less than 1.00, and have an angle of repose measured in accordance with ISO 4324 of 31.0° to 50.0°, and the first-stage expanded resin particles comprise a polymer material and at least one additive, and the additive exhibits a higher absorption rate of infrared rays than the polymer material.

12. The method according to claim 11, wherein the expansion ratio obtained by dividing the density of the first-stage expanded resin particles by the density of the expanded beads is in the range of 1.5 to 5.

0.

13. The method according to claim 11 or 12, wherein the value obtained by dividing the angle of repose of the expanded beads by the first angle of repose of the first-stage expanded resin particles is in the range of 1.15 to 2.

00.

14. A method for producing a molded product using the expanded beads according to any one of claims 1 to 10, comprising at least the following steps: supplying the expanded beads to a cavity of a molding die; and molding the expanded beads to produce a molded product.

Images