Thermoplastic resin expanded beads and thermoplastic resin expanded beads molded article

Abstract

The thermoplastic resin foamed particles of the present invention comprise conductive carbon material and flame retardant, and the thermoplastic resin foamed particles comprise: a foamed coating layer composed of thermoplastic resin and a core layer composed of thermoplastic resin, wherein the mass ratio of the coating layer to the core layer is 99:1 to 50:50, the conductive carbon material is selected from one or more of carbon nanotubes, carbon nanofibers, carbon nanostructures and graphene, the content of conductive carbon material in the core layer is 1% to 30% by mass, the content of conductive carbon material in the coating layer is 3% by mass or less (including 0%), the content of flame retardant in the coating layer is 5% to 25% by mass, the content of conductive carbon material in the coating layer is less than the content of conductive carbon material in the core layer, and the ratio of the content of flame retardant in the core layer to the content of conductive carbon material in the core layer is 0.2 or more.

Description

Technical Field

[0001] The present invention relates to thermoplastic resin foam particles and a thermoplastic resin foam particle molded body. More specifically, it relates to thermoplastic resin foam particles containing a conductive carbon material and a flame retardant, and a thermoplastic resin foam particle molded body using the thermoplastic resin foam particles. Prior Art

[0002] Thermoplastic resin foam particles can be molded into various shapes according to the application. The thermoplastic resin foam particle molded body obtained by in-mold molding of the foam particles can be used in a wide range of applications such as dielectrics, electromagnetic wave shields, heat insulators, packaging materials for electronic parts, shock absorbers, and transport boxes. For example, Patent Document 1 discloses thermoplastic resin foam particles containing functional additives.

[0003] On the other hand, for example, when using a thermoplastic resin foam particle molded body as an electromagnetic wave absorber, a conductive agent must be added as a functional additive. However, since a conductive agent with high conductivity has a self-igniting property, if the molded body as an electromagnetic wave absorber is exposed to a strong electric field, there is a risk of the molded body generating heat and catching fire. Also, in order to ensure higher electromagnetic wave absorption performance, if a large amount of a highly conductive conductive agent is added, there is a problem that the possibility of further heating and catching fire becomes higher.

[0004] Regarding such problems, a molded body has been proposed which is formed by adding a carbon material such as carbon black or graphite as a conductive agent and a flame retardant to a thermoplastic resin in order to prevent ignition accompanied by heat generation of an electromagnetic wave absorber composed of a thermoplastic resin foam particle molded body (for example, Patent Document 2). [Prior Art Documents] [Patent Documents]

[0005] [Patent Document 1] International Publication No. 2016 / 199693 [Patent Document 2] Japanese Patent Application Laid-Open No. 4-155899 Summary of the Invention Problems to be Solved by the Invention

[0006] However, as proposed in Patent Document 2, when a carbon material such as carbon black is used as a conductive agent and a flame retardant is added to form a molded body, the conductive agent detaches from the surface of the molded body, and contamination caused by the detached carbon material is likely to occur, and there is a problem that it is difficult to achieve both low contamination and flame retardancy.

[0007] The present invention is made in view of the above-mentioned conventional problems, and the object is to provide a thermoplastic resin foam particle, which can obtain a thermoplastic resin foam particle molded body containing a conductive carbon material, having excellent flame retardancy, and suppressing contamination caused by the detachment of the conductive carbon material. The means to solve the problem

[0008] The present invention provides the following thermoplastic resin foamed particles. <1> A thermoplastic resin foamed particle comprises a conductive carbon material and a flame retardant, wherein the thermoplastic resin foamed particle comprises: a foamed coating layer composed of a thermoplastic resin, and a core layer composed of a thermoplastic resin, wherein the mass ratio of the coating layer to the core layer is 99:1 to 50:50, wherein the conductive carbon material is selected from one or more of carbon nanotubes, carbon nanofibers, carbon nanostructures, and graphene, and wherein the content (Xi) of the conductive carbon material in the core layer is 1% by mass or more. The present invention relates to a composite material comprising a conductive carbon material and a coating layer, wherein the content of the conductive carbon material in the coating layer is less than 3% by mass (including 0), the content of the flame retardant in the coating layer (Yo) is not less than 5% by mass and not more than 25% by mass, the content of the conductive carbon material in the coating layer (Xo) is less than the content of the conductive carbon material in the core layer (Xi), and the ratio (Yi / Xi) of the content of the flame retardant in the core layer (Yi) to the content of the conductive carbon material in the core layer (Xi) is not less than 0.2. <2> like <1> The thermoplastic resin foamed particles, wherein the content (Yo) of the flame retardant in the coating layer is greater than the content (Yi) of the flame retardant in the core layer. <3> like <1> or <2> In the thermoplastic resin foamed particles, the conductive carbon material is carbon nanotubes. <4> like <1> to <3> The thermoplastic resin foamed particles described in any one of the above, wherein the apparent density of the thermoplastic resin foamed particles is 25 to 150 kg / m3. <5> like <1> to <4> The thermoplastic resin foamed particles described in any one of the above, wherein the thermoplastic resin forming the core layer and the thermoplastic resin forming the covering layer are both polyolefin resins. <6> like <1> to <5> The thermoplastic resin foamed particles described in any one of the above items, wherein the average bubble diameter of the coating layer is 50 μm or more and 300 μm or less. <7> like <1> to <6> The thermoplastic resin expanded particles described in any one of the above, wherein the core layer is a core layer in a foamed state, and the average bubble diameter of the core layer is greater than or equal to 5 μm and less than 50 μm. <8>The thermoplastic resin foam particles according to any one of <1> to <7>, wherein the mass ratio of the coating layer to the core layer is 99:1 to 80:20. <9>A thermoplastic resin foam particle molded body is obtained by in-mold molding of the foam particles according to any one of <1> to <8>. Advantages of the Invention

[0009] According to the thermoplastic resin foam particles of the present invention, there can be provided thermoplastic resin foam particles that can obtain a thermoplastic resin foam particle molded body containing a conductive carbon material, having excellent flame retardancy, and suppressing contamination caused by the detachment of functional additives. Brief Explanation of Drawings

[0010] FIG. 1 schematically shows a schematic perspective view of an embodiment of the thermoplastic resin foam particles of the present invention. FIG. 2 is a schematic explanatory view showing a method for measuring the apparent density of the core layer and the coating layer in the thermoplastic resin foam particles. Embodiments

[0011] Hereinafter, embodiments for implementing the invention will be listed to explain the foam particles of the present invention in more detail. In FIG. 1, a schematic perspective view of an embodiment of the thermoplastic resin foam particles of the present invention is schematically shown.

[0012] [Thermoplastic Resin Foam Particles]​​​​​​​​​​​​​The coating layer of the expanded beads of the present invention is formed to cover the outer periphery of the core layer. The foam structure forming the coating layer comprises bubbles formed by foaming a thermoplastic resin. Conventionally, when expanded beads contain a large amount of conductive carbon material to exhibit radio wave absorption properties, in-mold molding of these expanded beads to form expanded bead molded articles can lead to reduced fusion rate and secondary expansion, as well as reduced dimensional stability and appearance. Furthermore, to improve fusion, the expanded beads must be formed by increasing the molding pressure or pre-pressurizing the expanded beads. However, increasing the molding pressure increases the shrinkage of the molded article, which can lead to reduced dimensional stability and appearance. Furthermore, pressurizing the expanded beads at high pressure requires a long pressurization step, which still presents challenges from a productivity perspective.

[0015] In contrast, the present invention comprises a foamed particle system composed of a core layer and a coating layer, and the following conditions are set: the respective layers are set at a specific mass ratio, the core layer contains a conductive carbon material, and the coating layer, on the other hand, has a lower content of conductive carbon material than the core layer. Furthermore, by foaming the coating layer, a decrease in the secondary foaming properties of the foamed particles is suppressed. Furthermore, during in-mold molding of the foamed particles, the coating layer can undergo secondary foaming, so the foamed particles are fully fused together to form a good foamed particle molded body. Therefore, the thermoplastic resin foamed particle molded body (hereinafter simply referred to as the foamed particle molded body) obtained from the foamed particles of the present invention can be formed into a foamed particle molded body with excellent secondary foaming properties, no reduction in fusion rate, and low shrinkage, despite the addition of a conductive carbon material.

[0016] 1, although the core layer and the cover layer of the two-layer foamed particles are illustrated, but within the scope of not hindering the effects of the present invention, other layers may be provided to form a multilayer.

[0017] (Thermoplastic resin) In the expanded particles of the present invention, examples of the thermoplastic resin forming the core layer and the covering layer include polyolefin resins such as polyethylene resins and polypropylene resins, polystyrene resins, polycarbonate resins, polyvinyl chloride resins, polymethacrylic resins, acrylonitrile resins, polyester resins, polyamide resins, thermoplastic polyurethane resins, and polymer blends thereof. Among these, polyolefin resins are preferably used.

[0018] When a mixed resin of a polyolefin resin and other resins is used, the polyolefin resin is preferably contained in an amount of 50% by mass or more, more preferably 70% by mass or more, even more preferably 90% by mass or more, and even more preferably 95% by mass or more.

[0019] Examples of the polyethylene resin include low-density polyethylene, high-density polyethylene, linear low-density polyethylene, ultra-low-density polyethylene, ethylene-vinyl acetate copolymers, ethylene-methyl methacrylate copolymers, ethylene-methacrylic acid copolymers, and ionomer resins whose molecules are cross-linked with metal ions.

[0020] Examples of the polypropylene resin include propylene homopolymers and propylene copolymers containing 50% by mass or more of propylene-derived structural units. Examples of such copolymers include copolymers of propylene with ethylene or an α-olefin having 4 or more carbon atoms, such as ethylene-propylene copolymers, propylene-butene copolymers, and propylene-ethylene-butene copolymers; propylene-acrylic acid copolymers; and propylene-maleic anhydride copolymers. Furthermore, these copolymers may be block copolymers, random copolymers, or graft copolymers.

[0021] Furthermore, from the perspective of facilitating uniform mixing of the conductive carbon material described below, it is preferred to use a non-crosslinked thermoplastic resin. Furthermore, the thermoplastic resins used in the core layer and the coating layer may be the same or different, but it is preferred that both the core layer and the coating layer be polyolefin-based resins.

[0022] (Conductive carbon material) The conductive carbon material used in the present invention is selected from at least one of carbon nanotubes, carbon nanofibers, carbon nanostructures, and graphene. Among these, carbon nanotubes are particularly suitable. The conductive carbon material is preferably a conductive agent with high conductivity and radio wave absorption properties. The shape of the conductive carbon material is not particularly limited; examples include sheets, fibers, and meshes formed from the material. Using the conductive carbon material in the aforementioned shapes minimizes product contamination by entanglement with the conductive agent and anchoring it to the thermoplastic resin.

[0023] Among the aforementioned conductive carbon materials, carbon nanotubes are preferred due to their excellent workability. When using carbon nanotubes, they can be either single-walled or multi-walled. Furthermore, carbon nanotubes can include both single-walled and multi-walled carbon nanotubes. Multi-walled carbon nanotubes are more preferred from the perspectives of workability and cost. The average outer diameter of the carbon nanotubes is preferably from 5 nm to 25 nm, and more preferably from 7 nm to 15 nm. Furthermore, the aspect ratio of the carbon nanotubes is preferably from 50 to 500, and more preferably from 100 to 200. The aspect ratio is calculated by dividing the average length of the carbon nanotubes by their average diameter. When the carbon nanotube size falls within the aforementioned range, the excellent dispersibility in the resin allows for uniform properties of each expanded particle, and stabilizes properties such as electrostatic capacitance. Furthermore, the conductive carbon material used in the present invention exhibits superior radio wave absorption performance, even with a small addition amount, compared to conductive carbon black. Therefore, for example, when the expanded particles of the present invention are used as a radio wave absorber through in-mold molding, the expanded particle molded article can achieve both excellent radio wave absorption performance and excellent flame retardancy.

[0024] Furthermore, the average diameter of carbon nanotubes can be measured, for example, by the following method. First, the expanded bead is approximately bisected along the AA cross section shown in Figure 1. The cross-section is photographed using a scanning electron microscope to obtain a cross-section image of the expanded bead. The diameters of the carbon nanotubes present in the cross-section image are measured at 50 randomly selected locations. The average of the obtained diameters can be used as the average diameter.

[0025] The average length of carbon nanotubes can be measured, for example, by the following method. First, similar to the measurement of the average diameter of carbon nanotubes described above, obtain a cross-section image of the expanded particles using a scanning electron microscope. Randomly select 50 carbon nanotubes from the image and measure the length of each nanotube by image analysis. Furthermore, if the carbon nanotubes are not straight but curved, the length can be measured along the shape of the nanotube using a curve meter or the like. The average of the lengths obtained in this manner can be used as the average length.

[0026] (Content of conductive carbon material in the core layer) The content (Xi) of the conductive carbon material in the core layer is 1% by mass or more and 30% by mass or less. To achieve excellent capacitance, it is preferably 2% by mass or more, more preferably 5% by mass or more, and even more preferably 10% by mass or more. On the other hand, to minimize contamination, it is preferably 25% by mass or less, more preferably 20% by mass or less, and even more preferably 15% by mass or less.

[0027] (Content of conductive carbon material in the coating layer) The content (Xo) of the conductive carbon material in the coating layer is 3% by mass or less (including 0). Furthermore, from the perspective of improving the foaming properties of the coating layer, it is preferably 2% by mass or less, more preferably 1% by mass or less, and even more preferably 0.5% by mass or less. Furthermore, the coating layer may not contain a conductive carbon material. Furthermore, in the present invention, the content (Xo) of the conductive carbon material in the coating layer is less than the content (Xi) of the conductive carbon material in the core layer.

[0028] (Flame retardants and flame retardant additives) Halogen-based flame retardants, such as brominated and chlorinated flame retardants, are preferred flame retardants for the expanded particles of the present invention in order to exhibit high flame retardancy. Among these, brominated flame retardants are particularly suitable because they can easily achieve high flame retardancy with a small amount of addition.

[0029] Examples of brominated flame retardants include brominated epoxy resins obtained by adding bromine to epoxy resins, hexabromobenzene, pentabromotoluene, ethylene bispentabromodiphenyl, decabromodiphenyl oxide, 2,3-dibromopropyl pentabromophenyl oxide, polybromophenyl indane, polypentabromobenzyl methacrylate, brominated styrene-butadiene-styrene, brominated polyphenylene ether, brominated polystyrene and other brominated aromatic compounds or their derivatives, ethylene bis(tetrabromophthalimide), tris(tribromophenoxy)tris(tetrabromophthalimide), and the like. , compounds containing bromine and nitrogen atoms such as ginsenoside (2,3-dibromopropyl) triisocyanate, halogenated aliphatic compounds such as tetrabromocyclooctane, brominated bisphenol A such as tetrabromobisphenol A bis(2-bromoethyl) ether and tetrabromobisphenol A diallyl ether and their derivatives, brominated bisphenol S such as tetrabromobisphenol S and tetrabromobisphenol S (2-bromoethyl) ether and their derivatives, brominated bisphenol S derivatives such as tetrabromobisphenol A polycarbonate oligomers and tetrabromobisphenol epoxy oligomers, halogen-containing phosphorus compounds such as ginsenoside (tribromoneopentyl) phosphate and ginsenoside (bromophenyl) phosphate, etc.

[0030] In particular, tetrabromobisphenol A bis(2,3-dibromopropyl ether) and bis[3,5-dibromo-4-(2,3-dibromopropyloxy)phenyl]sulfonium are preferred because they exhibit high flame retardancy even with a small amount of addition.

[0031] To achieve excellent flame retardancy with a small amount of addition, the bromine content of brominated flame retardants is preferably 60% by mass or greater, and more preferably 63% by mass or greater. The bromine content can be determined in accordance with JIS K7392:2009.

[0032] The flame retardant preferably has a 5% decomposition temperature in the range of 260 to 340°C. By having the flame retardant's 5% decomposition temperature within this range, the brominated flame retardant can exhibit a sufficient flame retardant effect within the temperature range of resin thermal decomposition. From a similar perspective, the flame retardant's 5% decomposition temperature is preferably between 270 and 320°C, and more preferably between 285 and 305°C. Furthermore, the flame retardant's 5% decomposition temperature can be measured using a differential thermal thermogravimetric (TG / DTA) apparatus. Specifically, a differential thermal decomposition curve is measured under the following measurement conditions: a heating rate of 10°C / minute, a measurement temperature range of 40°C to 500°C, a nitrogen atmosphere, a sample pan material of Pt, and a sample mass of 10 mg. The 5% decomposition temperature is determined by measuring the temperature at which the weight decreases by 5% in the differential thermal decomposition curve.

[0033] In the present invention, the flame retardant and flame retardant auxiliary agent may be added. Examples of flame retardant auxiliary agents include metal hydroxide, polysilicone, Teflon, montmorillonite, metal oxides, trifluoromethane, and trifluoromethane. Compounds, guanidine compounds, etc. Among these, metal oxides that can be used in combination with brominated flame retardants to achieve a synergistic effect are suitable.

[0034] Examples of metal oxides include zinc borate, zinc stannate, antimony trioxide, and antimony pentoxide. Among these, antimony trioxide and zinc stannate are particularly suitable because they exhibit sufficient effects even with a small amount.

[0035] (Content of flame retardant and flame retardant additive in the core layer) The content (Yi) of the flame retardant in the core layer is preferably 1% by mass or greater, more preferably 2% by mass or greater, even more preferably 3% by mass or greater, and even more preferably 4% by mass or greater. Furthermore, the content (Yi) of the flame retardant in the core layer is preferably 15% by mass or less, more preferably 12% by mass or less, even more preferably 10% by mass or less, and even more preferably 8% by mass or less.

[0036] The content of the flame retardant additive in the core layer is preferably 0.5% by mass or greater, more preferably 1% by mass or greater, even more preferably 1.5% by mass or greater, and even more preferably 2% by mass or greater. Furthermore, the content of the flame retardant additive in the core layer is preferably 8% by mass or less, more preferably 6% by mass or less, even more preferably 5% by mass or less, and even more preferably 4% by mass or less. By setting the contents of the flame retardant and flame retardant additive within the aforementioned ranges, the expanded particles can be provided with both high functionality and high flame retardancy.

[0037] (Content of flame retardant and flame retardant additive in the coating layer) The flame retardant content (Yo) in the coating layer is within a range of 5% by mass to 25% by mass. To achieve high flame retardancy, the flame retardant content (Yo) in the coating layer is preferably 6% by mass or greater, more preferably 6.5% by mass or greater, and even more preferably 7% by mass or greater. On the other hand, to enhance secondary foaming properties, the flame retardant content (Yo) in the coating layer is preferably 20% by mass or less, more preferably 15% by mass or less, and even more preferably 12% by mass or less.

[0038] Furthermore, from the perspective of imparting high flame retardancy, the content of the flame retardant additive in the coating layer is preferably 2.5% by mass or greater, more preferably 3% by mass or greater, and even more preferably 3.5% by mass or greater. Furthermore, from the perspective of secondary foaming properties, the content of the flame retardant additive in the coating layer is preferably 10% by mass or less, more preferably 7.5% by mass or less, and even more preferably 6% by mass or less.

[0039] Furthermore, the flame retardant content (Yo) in the coating layer is preferably greater than the flame retardant content (Yi) in the core layer. Satisfying the aforementioned relationship regarding the flame retardant content is more preferable because excellent flame retardancy can be easily ensured.

[0040] (Other additives, etc.) The coating layer and core layer of the thermoplastic resin foam particles of the present invention may contain additives as needed. Examples of such additives include antioxidants, UV inhibitors, pigments, dyes, nucleating agents, lubricants, and compatibilizers. These additives may be used to the extent that they do not hinder the effects of the present invention. The amount of each additive added is preferably 5 parts by mass or less, and more preferably 3 parts by mass or less, per 100 parts by mass of the thermoplastic resin constituting each layer.

[0041] (Mass ratio of core layer to coating layer) In the thermoplastic resin expanded particles of the present invention, the mass ratio of the coating layer to the core layer is between 99:1 and 50:50. By setting the mass ratio of the coating layer to the core layer within the aforementioned range, the core layer, which contains a large amount of conductive carbon material, is securely covered by the coating layer, allowing the coating layer to expand, while also ensuring secondary expansion. This allows for a greater amount of conductive carbon material to be incorporated while also achieving expanded particles with excellent fusion properties during molding and dimensional stability of the molded product. From this perspective, a preferred range is 99:1 to 60:40, more preferably 99:1 to 80:20, and even more preferably 95:5 to 90:10. The aforementioned mass ratios include the mass of both the thermoplastic resin and the conductive carbon material contained therein.

[0042] Furthermore, in the expanded particles of the present invention, even if the core layer is completely covered by the covering layer, a portion of the core layer may be exposed. Examples of such structures include structures in which only the sides of a cylindrical core layer are covered by the covering layer, with the core layer exposed on the top and / or bottom surfaces of the cylinder.

[0043] [Functions of Thermoplastic Resin Foamed Particles] In the thermoplastic resin expanded particles of the present invention, while the core layer contains a conductive carbon material and a flame retardant, the ratio (Yi / Xi) of the flame retardant content (Yi) in the core layer to the conductive carbon material content (Xi) in the core layer is 0.2 or greater. By setting the ratio (Yi / Xi) of the conductive carbon material content (Xi) to the flame retardant content (Yi) in the core layer to the aforementioned conditions, it is possible to simultaneously incorporate the conductive carbon material and impart flame retardancy. From this perspective, the ratio (Yi / Xi) is preferably 0.3 or greater, more preferably 0.4 or greater. Furthermore, the ratio (Yi / Xi) is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less.

[0044] Furthermore, in the expanded particles of the present invention, as long as the effects of the present invention are not hindered, the expanded particles may also be configured to have other layers in addition to the core layer and the covering layer, for example, as the outermost layer or between the core layer and the covering layer.

[0045] According to the expanded beads of the present invention, which meet the aforementioned conditions, even if the expanded beads as a whole contain large amounts of conductive carbon material and flame retardant, the secondary expansion of the thermoplastic resin expanded beads is not impaired, and the fusibility of the expanded bead molded article is maintained. Therefore, even without increasing the molding pressure or pre-pressurizing the expanded beads during molding, the expanded beads still contain large amounts of conductive carbon material and flame retardant, while simultaneously producing an expanded bead molded article with a high fusibility, excellent secondary expansion, and suppressed shrinkage. Furthermore, the conductive carbon material and flame retardant can be varied in type and amount in the thermoplastic resin expanded bead molded article formed using the thermoplastic resin expanded beads, thereby enabling the production of expanded bead molded articles endowed with a variety of functionalities.

[0046] {Method for producing thermoplastic resin foamed particles] The expanded particles of the present invention can be produced, for example, by the following method. First, two extruders are prepared. A thermoplastic resin composition for forming the core layer is kneaded in one extruder, and a thermoplastic resin composition for forming the coating layer is kneaded in the other extruder. After this, the extruders are co-extruded through a die of a predetermined shape to produce a core-sheath-type rope-shaped composite composed of a core layer and a coating layer covering the core layer. The co-extruded rope-shaped composite is then cut into a predetermined mass or size using a cutter equipped with a drawing mechanism. This produces columnar composite resin particles composed of the core layer and the coating layer.

[0047] Expanded particles, which are foamed materials of resin particles, can be produced by the following methods: a conventionally known extrusion foamed particle production method, a method of releasing expandable resin particles containing a blowing agent from a pressurized sealed container to foam them, or a method of heating and softening expandable resin particles containing a blowing agent to foam them. Among the aforementioned production methods, the expandable particles of the present invention are preferably produced by dispersing composite resin particles consisting of a core layer and a coating layer in an aqueous medium (usually water) in a pressurized sealed container (e.g., an autoclave), adding a dispersant, pressurizing the desired amount of blowing agent, stirring under heating for the desired time to impregnate the composite resin particles with the blowing agent, and then releasing the contents from the container pressure to a low-pressure region along with the aqueous medium to foam them. The method of releasing expandable resin particles containing a blowing agent from a sealed container and foaming them is preferred because it is easy to set the average cell diameter of the coating layer and the foaming layer of the obtained expandable particles to a more preferred range described below.

[0048] As the blowing agent, any organic or inorganic physical blowing agent commonly used for foaming thermoplastic resins can be used. Examples of organic physical blowing agents include aliphatic hydrocarbons such as propane, butane, pentane, hexane, and heptane, and alicyclic hydrocarbons such as cyclobutane and cyclohexane. Examples of inorganic physical blowing agents include air, nitrogen, carbon dioxide, oxygen, argon, and water.

[0049] Examples of dispersants include poorly water-soluble inorganic substances such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica; and water-soluble polymeric protective colloids such as polyvinyl pyrrolidone, polyvinyl alcohol, and methylcellulose. Furthermore, anionic surfactants such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate can be used.

[0050] (Apparent density) The apparent density of the expanded particles of the present invention is preferably 25 to 150 kg / m³. By setting the apparent density of the expanded particles within this range, excellent lightweight properties and moldability can be achieved. From this perspective, the apparent density is more preferably 30 to 125 kg / m³, and even more preferably 35 to 100 kg / m³.

[0051] The apparent density of expanded particles is determined by preparing a graduated cylinder filled with 23°C water. A group of expanded particles (weight W [g]) is submerged in the cylinder using a metal mesh or other means. The volume V [cm3] of the expanded particles is calculated from the rise in the water level. This can be calculated by dividing the weight of the expanded particles by the volume of the expanded particles (W / V) and converting it to [kg / m3].

[0052] (Independent bubble rate) From the perspective of foaming moldability, the closed cell ratio of the expanded beads is preferably 80% or greater, more preferably 85% or greater, and even more preferably 90% or greater. Furthermore, the closed cell ratio of the expanded beads is determined according to the following procedure. Using expanded beads that have been stored in a constant temperature chamber for at least 10 days as test specimens, the apparent volume Va is accurately measured using the aforementioned method for measuring the apparent density of expanded beads (water immersion method). After the test specimens for which the apparent volume Va has been measured are thoroughly dried, the true volume Vx of the test specimens is measured using an "Air Comparative Density Meter 930" manufactured by Toshiba Beckman Co., Ltd., or similar instrument, according to procedure C of ASTM-D2856-70. Based on these volume values ​​Va and Vx, the closed cell ratio is calculated according to the following formula, and the average value of the values ​​for five samples (N=5) is used as the closed cell ratio of the expanded beads. Independent cell rate (%) = (Vx-W / ρ) × 100 / (Va-W / ρ) but, Vx: The true volume of the expanded particles measured by the above method, that is, the sum of the volume of the resin constituting the expanded particles and the total volume of the bubbles in the independent cell part of the expanded particles (cm3) Va: The apparent volume of the foamed particles measured from the part rising from the water level when the foamed particles are submerged in a graduated cylinder filled with water (cm3) W: Weight of the sample for foamed particles measurement (g) ρ: Density of the resin that makes up the foamed particles (g / cm3)

[0053] (Average bubble diameter of coating layer) In the expanded beads of the present invention, the average cell diameter of the coating layer is preferably 50 μm to 300 μm. From the perspective of obtaining an expanded bead molded article having excellent secondary expansion properties and low shrinkage, the average cell diameter of the coating layer is more preferably 55 μm to 250 μm, even more preferably 60 μm to 200 μm, and particularly preferably 60 μm to 100 μm.

[0054] The core layer can be either foamed or substantially non-foamed. From the perspective of easily exhibiting excellent capacitance, a foamed core layer is preferred. When the core layer is foamed, the average cell diameter of the core layer is preferably smaller than that of the coating layer, more preferably less than 50 μm, even more preferably 40 μm or less, and even more preferably 35 μm or less. Furthermore, the average cell diameter of the core layer is more preferably 5 μm or greater. When the average cell diameter of the core layer falls within the aforementioned range, excellent capacitance is more easily exhibited. Furthermore, the term "substantially non-foamed" encompasses not only a core layer completely devoid of bubbles (including one in which bubbles temporarily formed during foaming of the expanded particles are destroyed by melting, thus eliminating the bubbles) but also includes a core layer with only a slight presence of extremely fine bubbles. When the core layer is in a foamed state, the ratio of the average bubble diameter of the coating layer to the average bubble diameter of the core layer (average bubble diameter of the coating layer / average bubble diameter of the core layer) is preferably 1.5 to 8, and more preferably 2 to 5.

[0055] The average cell diameter of the coating layer and core layer is determined by bisecting the expanded bead along the AA section shown in Figure 1 and taking a magnified microscopic photograph of the cut surface as follows. First, a perpendicular bisector, l, is drawn through the center of the expanded bead cut surface, perpendicular to the line segment that takes the shortest distance from the top to the bottom. The length of line segment l, passing through the left to right end of the expanded bead, is measured. This length is designated as Lc (μm). The number of cells intersecting line l, Nc, is determined. The value Lc / Nc, divided by N, is used as the average cell diameter of the core layer of a single expanded bead. Draw a curve from the upper end surface through the inner side of 100 μm from the right end surface to the left end surface. Calculate the length Ls (μm) and the number Ns (cells) of bubbles intersecting the curve. Divide Ls by Ns (Ls / Ns) as the average bubble diameter of the coating layer of one foamed particle.

[0056] Furthermore, the core layer preferably has a higher density than the cover layer, described later. The following method can be used to confirm that the core layer has a higher density than the cover layer. Randomly select 20 or more expanded beads and cut them into three equal parts, A, B, and C, as shown in Figure 2. Next, use A + C as expanded bead sheet I and B as expanded bead sheet II. The apparent densities of each are determined using the same method as described for the apparent density of the expanded beads. From these apparent density results, the apparent density ratio (expanded bead sheet II / expanded bead sheet I) is calculated. If the apparent density ratio (expanded bead sheet II / expanded bead sheet I) is greater than 1, the core layer is considered to have a higher density than the cover layer. The apparent density ratio (expanded bead sheet II / expanded bead sheet I) is preferably greater than 1.0, more preferably greater than 1.1, and even more preferably greater than 1.2.

[0057] (Heat of fusion of high temperature peak) When the expanded beads of the present invention are polyolefin resin expanded beads, they preferably have secondary crystals, and the heat of fusion (high-temperature peak heat) of the high-temperature peak obtained by differential thermal analysis of the secondary crystals is 1 to 30 J / g. Specifically, when 2 to 10 mg of the polyolefin resin expanded beads are heated from 23°C to 220°C at a heating rate of 10°C / min using heat flux differential scanning calorimetry (DSC curve for the first heating), the DSC curve preferably exhibits an endothermic peak A (intrinsic peak) having a peak temperature intrinsic to the polyolefin resin, and one or more endothermic peaks B (high-temperature peaks) originating from the secondary crystals, having a peak temperature in the higher-temperature region of the intrinsic peak. Furthermore, the high-temperature peak heat is preferably 1 to 30 J / g, and even more preferably 5 to 20 J / g. A high-temperature peak heat within the aforementioned range allows for the production of an expanded bead molded article having excellent moldability. The high-temperature peak heat quantity corresponds to the area of ​​the high-temperature peak. Specifically, it can be calculated as follows. First, draw a straight line (α-β) connecting point α on the DSC curve, corresponding to 80°C, and point β on the DSC curve, corresponding to the melt end temperature T of the expanded beads. Furthermore, the melt end temperature T is the temperature corresponding to the intersection of the high-temperature side DSC curve of high-temperature peak B and the high-temperature side baseline. Next, draw a straight line parallel to the vertical axis of the graph from point γ on the DSC curve, which touches the valley between intrinsic peak A and high-temperature peak B. The point where the straight line (α-β) intersects is σ. The area of ​​high-temperature peak B is the area enclosed by the curve of the high-temperature peak B portion of the DSC curve, the line segment (σ-β), and the line segment (γ-σ). This corresponds to the heat quantity of the high-temperature peak. Furthermore, the high-temperature peak B appears in the DSC curve of the expanded beads measured in the aforementioned manner for the first heating. However, the DSC curve for the second heating, obtained after the first heating DSC curve, when the particles are cooled from 200°C to 25°C at a cooling rate of 10°C / min and then heated to 200°C at a heating rate of 10°C / min, does not appear. Instead, the DSC curve for the second heating shows only an endothermic peak identical to the intrinsic peak A. Therefore, the intrinsic peak A and the high-temperature peak B can be easily distinguished.

[0058] Furthermore, the expanded beads having a high temperature peak in the DSC curve can be obtained by heating the expanded resin beads in the expanded beads production step by stopping heating at a temperature 20°C lower than the melting point (Tm) of the polyolefin resin and at any temperature (Ta) within a range below the melting point (T) without raising the temperature to above the melting point (T) of the polyolefin resin during heating, and maintaining the temperature (Ta) for a sufficient time, preferably about 10 to 60 minutes (a first-stage maintenance step). Thereafter, the temperature is adjusted from 15°C lower than the melting point (Tm) to any temperature (Tb) within the range of the melting point (T) + 10°C, and if necessary, maintained at the temperature for a further sufficient time, preferably about 10 to 60 minutes. After maintaining the temperature (a second-stage maintenance step), the expanded resin beads are released from a sealed container under low pressure and expanded.

[0059] [Thermoplastic resin expanded particle molded article] The expanded particle molding system using the expanded particles of the present invention can be formed by in-mold molding using only the expanded particles of the present invention, or can be formed using the expanded particles of the present invention in combination with other commonly known thermoplastic resin expanded particles. The size and shape of the expanded particle molded article are not particularly limited and can be various three-dimensional shapes such as plates, columns, polygonal pyramids, and cones.

[0060] [Method for forming thermoplastic resin expanded particle molded article] Expanded particle molding systems can be produced, for example, using an in-mold molding method. Specifically, a mold designed to the desired shape is first prepared. Next, the mold is filled with the expandable particles of the present invention, and steam is supplied to heat the mold. During this process, the coating layers of adjacent expandable particles fuse together. Furthermore, the thermoplastic resin expandable particles undergo secondary expansion, filling the gaps between the expandable particles and integrating the plurality of expandable thermoplastic resin particles filled in the mold. The mold is then cooled, and the contents are removed from the mold to obtain an expandable particle molded article.

[0061] (Molding body density) The density of the expanded particle molded article of the present invention is not particularly limited, but is generally preferably between 9 and 300 kg / m³. The density can be calculated by dividing the mass of the molded article by its volume. The volume of the expanded particle molded article can be calculated based on the molded article's external dimensions.

[0062] (Fusion rate) In order to obtain a foamed bead molded article having excellent dimensional stability or appearance, the fusion rate of the foamed beads constituting the foamed bead molded article should be 70% or higher, preferably 80% or higher, and more preferably 90% or higher.

[0063] The expanded particle molded article of the present invention preferably has an electrostatic capacitance of 0.12 to 0.4 pF, and more preferably 0.2 to 0.35 pF. If the electrostatic capacitance of the expanded particle molded article falls within this range, excellent radio wave absorption performance can be expected, and the molded article can be formed into a suitable article for use as a radio wave absorber. {Example]

[0064] Hereinafter, the present invention will be described in more detail by way of examples.

[0065] The following raw materials were used to adjust the raw material masterbatch (MB) to obtain thermoplastic resin foamed particles of Examples 1 to 10 shown in Table 5 and Comparative Examples 1 to 5 shown in Table 6. (raw material) As raw materials, the following thermoplastic resin, conductive carbon material, flame retardant, and flame retardant auxiliary agent were used. Thermoplastic resin: Polypropylene resin shown in Table 1 Conductive carbon materials: Conductive carbon materials shown in Table 2 and Table 3 Flame retardants and flame retardant additives: flame retardants and flame retardant additives shown in Table 4

[0066] [Table 1]

[0067] [Table 2]

[0068] [Table 3]

[0069] [Table 4]

[0070] [Preparation of raw material masterbatch (MB)] The polypropylene resin shown in Table 1, the conductive carbon materials shown in Tables 2 and 3, the flame retardant shown in Table 4, and the flame retardant additives were supplied to a two-screw extruder with an inner diameter of 20 mm in the proportions shown in Tables 5 and 6 below, respectively. They were melt-kneaded at 150 to 190° C. and extruded into strands. The strands were cooled and cut to obtain masterbatches for forming the core and cladding layers of Examples 1 to 10, Comparative Examples 1, 2, 4, and 5, and a masterbatch for forming the core layer of Comparative Example 3.

[0071] [Manufacturing of thermoplastic resin particles (resin particles)] (Example 1) Using a single-layer extruder for a resin particle core layer with an inner diameter of 25 mm and a twin-screw extruder for a resin particle coating layer with an inner diameter of 26 mm, each extruder had a multilayer strand-forming die attached to the outlet. The formulations shown in Table 5 were obtained. The core layer masterbatch was supplied to the 25 mm inner diameter resin particle core extruder, while the coating layer masterbatch was simultaneously supplied to the 26 mm inner diameter resin particle coating extruder. The masterbatch was heated to a set temperature of 190 to 210°C, melted, and kneaded before being supplied to the die. The strands were then combined within the die and co-extruded through a fine orifice in a metal cap mounted on the front end of the extruder to form a multilayer strand with the coating layer covering the sides of the core layer. The co-extruded strands were then water-cooled and cut into 2 mg pieces using a pelletizer with an L / D ratio of 2.4, yielding the resin particles shown in Table 5, each having a two-layer (sheath-core) cylindrical shape. Furthermore, zinc borate was added to the coating layer at a concentration of 1000 ppm by mass as a bubble control agent. Furthermore, the mass ratio of the core layer to the coating layer was set at 7:93.

[0072] [Manufacturing of Thermoplastic Resin Expanded Particles (Expanded Particles)] 1 kg of the aforementioned resin particles and 3 L of water as a dispersion medium were loaded into a 5 L autoclave. 3 g of kaolin as a dispersant, 0.04 g of sodium alkylbenzene sulfonate as a dispersing aid, and 0.1 g of aluminum sulfate were added to the dispersion medium. Carbon dioxide was then pressurized into the closed container as a blowing agent at the pressure indicated in Table 5. The mixture was heated to the foaming temperature with stirring and maintained at the same temperature for 15 minutes. After adjusting the peak heat, the contents of the autoclave were released at atmospheric pressure along with the water to obtain expanded particles.

[0073] [Manufacturing of Thermoplastic Resin Expanded Bead Molded Articles] The expanded beads obtained above were filled into a flat-plate molding cavity measuring 250 mm (long side) x 200 mm (width) x 50 mm (thickness). In-mold molding using steam heating was performed to obtain a sheet-shaped foamed molded article. The heating method involved preheating (exhausting) the mold by supplying steam for 5 seconds with both mold drain valves open. The mold was then heated from one side at a pressure 0.04 MPa (G) lower than the preheating pressure. Furthermore, the mold was heated from the opposite side at a pressure 0.02 MPa (G) lower than the preheating pressure. Finally, the mold was heated at the molding steam pressure (molding pressure) shown in Table 5. (G) refers to gauge pressure.

[0074] The molding pressure represents the minimum pressure required to obtain a molded article with excellent appearance without significant shrinkage. After heating, the pressure was released and the mold was water-cooled until the surface pressure due to the foaming force of the molded article reached 0.04 MPa(G). The mold was then opened and the molded article removed. The resulting molded article was aged in an 80°C oven for 12 hours to obtain an expanded bead molded article. The physical properties of the resulting expanded bead molded article are shown in Table 5.

[0075] (Examples 2 to 10) Except that the manufacturing conditions were set to the conditions shown in Table 5, the same method as in Example 1 was used to obtain resin particles, foamed particles, and foamed particle molded bodies.

[0076] (Comparative Examples 1 to 5) Comparative Examples 1, 2, 4, and 5 were prepared using the same method as Example 1, except that the manufacturing conditions were set to those shown in Table 6. In Comparative Example 3, only the core layer masterbatch was prepared using the formulation shown in Table 6. This was fed to a resin particle core layer extruder with an inner diameter of 25 mm, heated to a set temperature of 190 to 210°C, melted, and kneaded. The extruder then extruded the strands through the orifice of a metal cap attached to the front end of the extruder to form single-layer strands. The strands were then water-cooled and cut into 2 mg pieces using a pelletizer with an L / D ratio of 2.4, yielding the resin particles described in Table 6, each having a single layer and cylindrical shape. Subsequently, the expanded particle molded articles were obtained using the same procedure as in Example 1.

[0077] In Tables 5 and 6, the term "coating layer / core layer (mass ratio)" refers to the mass ratio (%) of the coating layer to the core layer relative to the total mass of the particle. The extrusion processability of each resin pellet was evaluated according to the following criteria. The results are shown in Tables 5 and 6. ○(good): No pulsation occurs when squeezing (no subtle changes in the discharge of each strand), and the strand thickness is always constant. △(poor): There is a slight pulsation when squeezing (some subtle changes in the exhalation of each strand), and the thickness of the strand changes only slightly.

[0078] The physical properties of the expanded beads and expanded bead molded articles of Examples 1 to 10 and Comparative Examples 1 to 5 were measured and evaluated according to the following methods. The results are shown in Tables 5 and 6. (Apparent density of expanded particles) The apparent density of expanded particles is calculated using the following procedure. First, prepare a graduated cylinder filled with 23°C water. Use a metal mesh to submerge the expanded particles (weight W [g]) in the cylinder. Calculate the volume V [cm³] of the expanded particles from the rise in the water level. Divide the weight of the expanded particles by the volume (W / V) and convert to [kg / m³] to obtain the apparent density.

[0079] (ratio of apparent density) The apparent density ratio is determined using the following method. First, 20 randomly selected expanded beads are cut into three equal parts, A, B, and C, at equal intervals, as shown in Figure 2. A + C is designated as expanded bead sheet I, and B is designated as expanded bead sheet II. The apparent density of each is determined using the same method as described above for the apparent density of the expanded beads. From these apparent density results, the apparent density ratio (expanded bead sheet II / expanded bead sheet I) is determined.

[0080] (Independent bubble ratio of expanded particles) The closed cell ratio of expanded beads is measured using the following procedure. A sample of approximately 20 cm³ of expanded beads, stored in a constant temperature chamber for 10 days, is used as a test sample. The apparent volume Va is accurately measured using the aforementioned method for measuring the apparent density of expanded beads (water submersion method). After the sample with the measured apparent volume Va is thoroughly dried, the true volume Vx of the sample is measured using an "Air Comparative Density Meter 930" manufactured by Toshiba Beckman Co., Ltd., according to procedure C of ASTM-D2856-70. Based on these volume values ​​Va and Vx, the closed cell ratio is calculated using the following formula. The average value of the five samples (N=5) is used as the closed cell ratio of the expanded beads. Independent cell rate (%) = (Vx-W / ρ) × 100 / (Va-W / ρ) but, Vx: The true volume of the expanded particles measured by the above method, that is, the sum of the volume of the resin constituting the expanded particles and the total volume of the bubbles in the independent cell part of the expanded particles (cm3) Va: The apparent volume of the foamed particles measured from the part rising from the water level when the foamed particles are submerged in a graduated cylinder filled with water (cm3) W: Weight of the sample for foamed particles measurement (g) ρ: Density of the resin that makes up the foamed particles (g / cm3)

[0081] (Average bubble diameter of coating layer and core layer) The average cell diameter of the coating layer and core layer was measured using the following procedure. The expanded bead was approximately bisected along the AA section shown in Figure 1. Based on a magnified microscopic photograph of the cut surface, the average cell diameter was determined as follows. First, a perpendicular bisector, l, was drawn through the center of the expanded bead in the magnified microscopic photograph of the cut surface, perpendicular to the line segment that takes the shortest distance from the top to the bottom. The length of the line segment, l, from the left to the right end of the expanded bead passing through l, was measured. This length was designated Lc (μm). The number of cells intersecting the line, Nc, was determined. The value Lc / Nc, divided by N, was used as the average cell diameter of the core layer of the expanded bead. Draw a curve from the right end surface to the left end surface, passing 100 μm inside the upper end surface. Calculate the number Ns of cells where this length Ls (μm) intersects the curve. Divide Ls by Ns (Ls / Ns) to obtain the average cell diameter of the coating layer of one expanded bead. Repeat this procedure for 10 expanded beads, and take the average of the average cell diameters of the core and coating layers of each expanded bead as the average cell diameter of the core and coating layers of the expanded bead. In Comparative Example 3, only the average cell diameter of the core layer was calculated.

[0082] (High temperature peak heat of expanded particles) The high-temperature peak calorific value of the expanded particles was measured using the following procedure. The DSC curve (DSC curve for the first heating) obtained by heating 1 to 3 mg of the expanded particles from 25°C to 200°C at a heating rate of 10°C / minute using a heat flux differential scanning calorimeter showed an endothermic peak A (intrinsic peak) with a peak temperature inherent to the thermoplastic resin, and one or more endothermic peaks B (high-temperature peaks) with peak temperatures in the high-temperature region of the intrinsic peak. The high-temperature peak calorific value was calculated using the method described in the instructions. The average value of five randomly selected samples (N=5) was used as the high-temperature peak calorific value of the expanded particles.

[0083] (Fusion rate of expanded particle molding) The fusion rate is measured by measuring the ratio of the number of foamed particles that have been damaged by the material (fusion rate) among the foamed particles exposed at the fractured surface of the foamed particle molded article. Specifically, test pieces are cut from the foamed particle molded article. A cutter is used to make an approximately 5 mm incision in each test piece. The foamed particle molded article is then ruptured along the cut. The number of foamed particles (n) present at the fractured surface of the foamed particle molded article and the number of foamed particles that have been damaged by the material (b) are then measured. The ratio (b / n) of (b) to (n) is expressed as a percentage and is defined as the fusion rate (%).

[0084] (Density of expanded particle molding) The density of the expanded bead molded article (molded article density) is determined by dividing the mass (kg) of the molded article by the volume (m3) determined from the external dimensions of the molded article.

[0085] (Shrinkage) The shrinkage rate {%] of the expanded bead molded article is calculated as (250 [mm] - length of the long side of the molded article [mm]) / 250 [mm] × 100. "250 [mm]" refers to the long side dimension of the molding mold, and "length of the long side of the molded article [mm]" refers to the length of the long side of the expanded bead molded articles obtained in Examples and Comparative Examples, after aging at 80°C for 12 hours, followed by slow cooling, and further aging at 23°C for 6 hours.

[0086] (Secondary foaming) The secondary foaming property of the molded article was evaluated as follows. ○(good): The gaps between the foamed particles on the surface of the molded body are completely buried △(poor): The gaps between the foamed particles on the surface of the molded body can be roughly seen ×(bad): The gaps between the foamed particles on the surface of the molded body are not obviously buried.

[0087] (Flame retardancy) A rectangular test piece measuring 150 mm long x 50 mm wide x 13 mm thick was cut from approximately the center of the thickness of the expanded bead molded article (the molded skin layer remained on one side of the 150 mm long x 50 mm wide section). This was used as a test piece for the UL94 HBF test, which conforms to the flame retardancy standard. The resulting test piece was arranged with the molded skin layer positioned as shown below, and the UL94 HBF test was performed. Flame retardancy was evaluated according to the following evaluation criteria. ○(good): For all 5 test pieces, the burning speed between the 100mm markings is less than 40mm / min, the burning distance is less than 125mm, or both of the above are met. ×(bad): For one or more of the five test pieces, the burning speed between the 100mm markings exceeds 40mm / min, the burning distance is 125mm or more, or both of the above conditions are met.

[0088] (Electrostatic Capacitance) The electrostatic capacitance of the expanded bead molded article was measured using a capacitance measuring instrument CM113N manufactured by Yamamoto Electric Instruments Co., Ltd. A probe (A1407-8065) ​​was used, with a detection electrode diameter of 98 mm, a guide electrode outer diameter of 150 mm, an inner diameter of 100 mm, an electrode width of 50 mm, and an insulation distance of 2 mm between the electrodes. First, a metal plate, serving as the counter electrode, was placed on a horizontal surface. A 300 mm long x 300 mm wide x 200 mm thick polypropylene resin expanded bead molded article with a density of 30 kg / m³ and no conductive agent was placed on top of the metal plate as a blank. The blank was placed so that there was no gap between the metal plate and the guide electrode of the measuring probe. After this placement, the electrostatic capacitance was measured and the origin was adjusted. Subsequently, the measuring probe was placed on each expanded bead molded article (250 mm long x 200 mm wide x 50 mm thick) obtained in the Examples and Comparative Examples, and the electrostatic capacitance of the expanded bead molded article was measured.

[0089] (Pollution) The staining potential of the expanded particle molded article was evaluated by the degree of staining on fabric. The staining test method for fabric was as follows: A non-colored polypropylene rod (A) measuring 10 mm wide, 300 mm long, and 5 mm thick was fixed to a table. A No. 3 cotton muslin cloth measuring 100 mm wide and 200 mm long (B) was fixed to the rod (A). A test specimen (C) was cut out with the expanded particle molded article's molded skin remaining 50 mm x 50 mm on one side, measuring 50 mm x 50 mm x 25 mm thick. The molded skin of the expanded particle molded article was placed on the cloth (B) with the molded skin facing downward. A 3 kg hammer (D) was then placed on top of the cloth (B).

[0090] Secure the sample (C) and hammer (D) with a fixture and reciprocate over a white cloth (B). Compare the staining of the cloth using the L* value. The reciprocating motion is conducted with an amplitude of 200 mm, a frequency of 4.5 Hz, and a test duration of 10 seconds. Five tests are performed for each type of white cloth (B) and sample (C), varying the conditions.

[0091] The soiling degree of the fabric was evaluated as follows. The L* value (L*B) of the white fabric before the soiling test was measured. For each sample obtained from the five tests described above, the L* value (L*A) of the soiled portion of the white fabric after the soiling test was measured. The L*AL*B value (ΔL*) was calculated, and the arithmetic average of the ΔL* values ​​was used as the soiling degree. Furthermore, the L* value was measured using a spectrophotometer / colorimeter (CM-5, manufactured by Konica Minolta Japan) by measuring the mesh size of the measurement area: 8mm, Measurement method: Reflection measurement, SCE method conditions.

[0092] [Table 5]

[0093] [Table 6]

[0094] Since the foaming systems of Examples 1 to 10 have a core layer highly filled with conductive carbon material and a coating layer formulated with a flame retardant and foamed, the foamed particle molded body can be confirmed to contain a large amount of conductive carbon material by performing a second foaming during in-mold molding, and has a stable electrostatic capacitance. At the same time, a foamed molded body with excellent weldability, dimensional stability, flame retardancy, and anti-pollution properties can be obtained.

[0095] On the other hand, Comparative Example 1 uses carbon black as the conductive carbon material. Compared to the examples, the electrostatic capacitance is high, and detachment of the conductive carbon material is observed, indicating a high degree of contamination. Comparative Example 2 shows that the ratio (Yi / Xi) of the flame retardant content (Yi) in the core layer to the conductive carbon material content (Xi) in the core layer is lower than the requirement of the present invention. In other words, the flame retardant content (Yi) in the core layer is too low relative to the conductive carbon material content (Xi), indicating poor flame retardancy. Comparative Example 3 uses a single layer of expanded particles consisting only of the core layer. The secondary foaming properties are significantly poor, indicating a high degree of contamination. Comparative Example 4, in which the core layer is foamed and the conductive carbon material is incorporated into the coating layer, shows significantly poor flame retardancy and a high degree of contamination. Finally, Comparative Example 5 shows that the conductive carbon material content in the core layer is low, indicating a significantly low electrostatic capacitance.

Claims

1. A thermoplastic resin foamed particle comprising a conductive carbon material and a flame retardant, wherein the thermoplastic resin foamed particle comprises: a foamed coating layer made of thermoplastic resin and a core layer made of thermoplastic resin, wherein the mass ratio of the coating layer to the core layer is 99:1 to 50:50, the conductive carbon material is selected from one or more of carbon nanotubes, carbon nanofibers, nano-carbon structures, and graphene, and the content (Xi) of the conductive carbon material in the core layer is 1% by mass or more. The content of conductive carbon material (Xo) in the aforementioned coating layer is 3% by mass or less and includes 0%, the content of flame retardant (Yo) in the aforementioned coating layer is 5% by mass or more and 25% by mass or less, the content of conductive carbon material (Xo) in the aforementioned coating layer is less than the content of conductive carbon material (Xi) in the aforementioned core layer, and the ratio (Yi / Xi) of the content of flame retardant (Yi) in the aforementioned core layer to the content of conductive carbon material (Xi) in the aforementioned core layer is 0.2 or more.

2. The thermoplastic resin foam particles as described in claim 1, wherein, The content of flame retardant in the aforementioned coating layer (Yo) is greater than the content of flame retardant in the aforementioned core layer (Yi).

3. The thermoplastic resin foam particles as described in claim 1, wherein, The aforementioned conductive carbon material is a carbon nanotube.

4. The thermoplastic resin foam particles as described in claim 1, wherein, The apparent density of the aforementioned thermoplastic resin foam particles is 25 to 150 kg / m3.

5. The thermoplastic resin foam particles as described in claim 1, wherein, The thermoplastic resin forming the aforementioned core layer and the thermoplastic resin forming the aforementioned coating layer are both polyolefin resins.

6. The thermoplastic resin foam particles as described in claim 1, wherein, The average bubble diameter of the aforementioned coating layer is between 50 μm and 300 μm.

7. The thermoplastic resin foam particles as described in claim 1, wherein, The aforementioned core layer is a foamed core layer, and the average bubble diameter of the aforementioned core layer is greater than 5μm but less than 50μm.

8. The thermoplastic resin foam particles as described in claim 1, wherein, The mass ratio of the aforementioned coating layer to the aforementioned core layer is 99:1 to 80:

20.

9. A thermoplastic resin foamed particle molded body, formed by in-mold molding of the foamed particles described in any one of claims 1 to 8.

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