Expanded thermoplastic resin beads and expanded thermoplastic resin beads molded article

Abstract

To provide thermoplastic resin foam particles from which a thermoplastic resin foam particle molding that contains a conductive carbon material and is excellent in flame retardancy and suppresses contamination by desorption of the conductive carbon material can be obtained.SOLUTION: Thermoplastic resin foam particles contain a conductive carbon material and a flame retardant, wherein the thermoplastic resin foam particles are composed of a coating layer in a foam state composed of a thermoplastic resin and a core layer composed of a thermoplastic resin, a mass ratio of the coating layer to the core layer is 99:1 to 50:50, a carbon nanotube is used as the conductive carbon material, a content of the conductive carbon material in the core layer is 1 mass% or more and 30 mass% or less, a content of the conductive carbon material in the coating layer is 3 mass% or less, a content of the flame retardant in the coating layer is 5 mass% or more and 25 mass% or less, a content of the conductive carbon material in the coating layer is smaller than the content of the conductive carbon material in the core layer, and a ratio of the content of the flame retardant in the core layer to the content of the conductive carbon material in the core layer is 0.2 or more.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to expanded thermoplastic resin beads and expanded thermoplastic resin bead moldings, and more particularly to expanded thermoplastic resin beads containing a conductive carbon material and a flame retardant, and expanded thermoplastic resin bead moldings using the same. [Background technology]

[0002] Expanded thermoplastic resin beads can be molded into various shapes depending on the application. Expanded thermoplastic resin bead moldings obtained from the expanded beads by in-mold molding are used in a wide range of applications, such as dielectrics, radio wave shielding materials, heat insulating materials, packaging materials for electronic components, shock absorbing materials, and returnable containers. For example, Patent Document 1 discloses expanded thermoplastic resin beads containing functional additives.

[0003] On the other hand, for example, when a thermoplastic resin foamed bead molding is used as a radio wave absorber, it is necessary to add a conductive agent as a functional additive. However, since a highly conductive conductive agent has a combustion-supporting property, there is a risk that the molding as a radio wave absorber will generate heat and catch fire when exposed to a strong electric field. Furthermore, there is a problem that adding a large amount of a highly conductive conductive agent in order to ensure higher radio wave absorption performance further increases the possibility of heat generation and fire.

[0004] To address this problem, in order to prevent ignition due to heat generation in a radio wave absorber made of a thermoplastic resin foam particle molding, a molding has been proposed in which a flame retardant is added to a thermoplastic resin together with a carbon material such as carbon black or graphite as a conductive agent (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 Publication No. 4-155899 Summary of the Invention [Problem 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 is detached from the surface of the molded body, and the detached carbon material is likely to cause contamination, making it difficult to achieve both low contamination and flame retardancy.

[0007] The present invention has been made in consideration of the above-mentioned conventional problems, and an object of the present invention is to provide expanded thermoplastic resin beads that can be used to obtain expanded thermoplastic resin bead moldings that contain a conductive carbon material but have excellent flame retardancy and are suppressed from being contaminated by detachment of the conductive carbon material. [Means for solving the problem]

[0008] The present invention provides the following expanded thermoplastic resin particles. <1> 1. Expanded thermoplastic resin particles comprising a conductive carbon material and a flame retardant, the expanded thermoplastic resin particles comprising an expanded coating layer made of a thermoplastic resin and a core layer made of a thermoplastic resin, the mass ratio of the coating layer to the core layer being 99:1 to 50:50, the conductive carbon material being one or more selected from carbon nanotubes, carbon nanofibers, carbon nanostructures, and graphene, the content of the conductive carbon material in the core layer (Xi) being 1% by mass or more and 30% by mass or less, the content of the conductive carbon material in the coating layer (Xo) being 3% by mass or less (including 0), the content of the flame retardant in the coating layer (Yo) being 5% by mass or more and 25% by mass or less, the content of the conductive carbon material in the coating layer (Xo) being 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 to the content of the conductive carbon material in the core layer (Xi) being 0.2 or more. <2> 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. <1> The thermoplastic resin foam particles according to claim 1. <3> The conductive carbon material is a carbon nanotube. <1> or <2> The thermoplastic resin foam particles according to claim 1. <4> The apparent density of the expanded thermoplastic resin particles is 25 to 150 kg / m 3 characterized in that <1> from <3> 2. The expanded thermoplastic resin particles according to any one of claims 1 to 11. <5> The thermoplastic resin forming the core layer and the thermoplastic resin forming the coating layer are both polyolefin resins. <1> from <4> 2. The expanded thermoplastic resin particles according to any one of claims 1 to 11. <6> The coating layer is characterized in that the average bubble diameter is 50 μm or more and 300 μm or less. <1> from <5> 2. The expanded thermoplastic resin particles according to any one of claims 1 to 11. <7> The core layer is a foamed core layer, and the average bubble diameter of the core layer is 5 μm or more and less than 50 μm. <1> from <6> 2. The expanded thermoplastic resin particles according to any one of claims 1 to 11. <8> The mass ratio of the coating layer to the core layer is 99:1 to 80:20. <1> from <7> 2. The expanded thermoplastic resin particles according to any one of claims 1 to 11. <9> <1> from <8> 2. A foamed thermoplastic resin bead molding obtained by molding the foamed beads according to any one of the preceding items in a mold. [Effects of the Invention]

[0009] According to the expanded thermoplastic resin beads of the present invention, it is possible to provide expanded thermoplastic resin beads that contain a conductive carbon material but have excellent flame retardancy and can produce expanded thermoplastic resin bead moldings that are inhibited from being contaminated by detachment of functional additives. [Brief explanation of the drawings]

[0010] [Figure 1] 1 is a schematic perspective view showing an embodiment of an expanded thermoplastic resin bead according to the present invention. [Figure 2]FIG. 2 is a schematic diagram illustrating a method for measuring the apparent density of the core layer and the coating layer of the expanded thermoplastic resin beads. BEST MODE FOR CARRYING OUT THE INVENTION

[0011] The expanded beads of the present invention will be described in more detail below with reference to embodiments for carrying out the invention. Fig. 1 is a schematic perspective view showing one embodiment of the expanded thermoplastic resin beads of the present invention.

[0012] [Thermoplastic resin foam particles] The expanded thermoplastic resin beads (hereinafter simply referred to as expanded beads) of this embodiment have a core layer formed from a thermoplastic resin and an expanded coating layer formed from a thermoplastic resin.

[0013] (Core layer) The core layer in the expanded beads of the present invention is formed from a thermoplastic resin and contains a conductive carbon material and a flame retardant as essential components.

[0014] (covering layer) The coating layer of the expanded beads of the present invention is a foamed layer formed to cover the outer periphery of the core layer, and the foamed structure forming the coating layer is a structure with bubbles formed by foaming a thermoplastic resin. Conventionally, when a large amount of conductive carbon material is incorporated into expanded beads to exhibit radio wave absorption performance, molding the expanded beads into an expanded bead molding in a mold can result in a decrease in the fusion rate and secondary foaming ability of the expanded bead molding, as well as a decrease in dimensional stability and appearance. On the other hand, in order to improve fusion property, it has been necessary to increase the molding pressure when molding the expanded beads or to pre-pressurize the expanded beads. However, increasing the molding pressure increases the shrinkage rate of the molded product, which tends to decrease dimensional stability and appearance. Furthermore, compressing the expanded beads at high pressure requires a long pressurization process, which leaves problems in terms of productivity.

[0015] In contrast, in the present invention, the expanded beads are composed of a core layer and a coating layer, with the respective layers being in a specific mass ratio, and the core layer contains a conductive carbon material, while the coating layer has a lower conductive carbon material content than the core layer. Furthermore, the expansion of the coating layer suppresses a decrease in the secondary expandability of the expanded beads. Furthermore, since the coating layer undergoes secondary expansion during in-mold molding, the expanded beads can be sufficiently fused together to form a good expanded bead molding. Therefore, despite the inclusion of a conductive carbon material, the expanded thermoplastic resin expanded bead molding (hereinafter simply referred to as the expanded bead molding) obtained from the expanded beads of the present invention can be an expanded bead molding with excellent secondary expandability, no decrease in fusion rate, and a small shrinkage rate.

[0016] In the embodiment shown in FIG. 1, a two-layer expanded bead consisting of a core layer and a coating layer is exemplified, but other layers may be further provided to form a multi-layer structure as long as the effects of the present invention are not impaired.

[0017] (thermoplastic resin) In the expanded beads of the present invention, examples of the thermoplastic resin forming the core layer and the coating 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 blend polymers thereof. Among these, polyolefin resins are preferably used.

[0018] Furthermore, when a mixed resin of a polyolefin resin and another resin is used, it is preferable that the mixed resin contains 50% by mass or more of the polyolefin resin, 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, very low-density polyethylene, ethylene-vinyl acetate copolymer, ethylene-methyl methacrylate copolymer, ethylene-methacrylic acid copolymer, and ionomer resins in which the molecules thereof are crosslinked with metal ions.

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

[0021] It is preferable to use a non-crosslinked thermoplastic resin because it is easy to form a state in which the conductive carbon material described later is uniformly mixed. The thermoplastic resins used in the core layer and the coating layer may be the same or different, but it is preferable that both the thermoplastic resins used in the core layer and the coating layer are polyolefin resins.

[0022] (Conductive carbon materials) The conductive carbon material used in the present invention is one or more selected from carbon nanotubes, carbon nanofibers, carbon nanostructures, and graphene, and among these, carbon nanotubes are preferably used. 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, and examples include sheets, fibers, and nets made of the material. By using a conductive carbon material in the above shape, the anchoring effect on the thermoplastic resin and the entanglement of the conductive agent itself make it difficult to detach, thereby minimizing product contamination.

[0023] Among the conductive carbon materials, carbon nanotubes are preferred due to their excellent handleability. When carbon nanotubes are used, they may be single-walled or multi-walled carbon nanotubes. Furthermore, the carbon nanotubes may include both single-walled and multi-walled carbon nanotubes. Multi-walled carbon nanotubes are preferred from the standpoints of handleability and cost. The average outer diameter of the carbon nanotubes is preferably 5 nm to 25 nm, more preferably 7 nm to 15 nm. Furthermore, the aspect ratio of the carbon nanotubes is preferably 50 to 500, more preferably 100 to 200. The aspect ratio is calculated by dividing the average length of the carbon nanotubes by the average diameter. When the carbon nanotube size is within the above range, the excellent dispersibility in the resin results in uniform properties for each expanded particle, stabilizing performance such as capacitance. Furthermore, the conductive carbon material used in the present invention can exhibit excellent radio wave absorption performance with a smaller amount added than conductive carbon black. Therefore, for example, when the foamed beads of the present invention are molded in a mold to form a foamed bead molding, the foamed beads can have both excellent wave absorbing properties and excellent flame retardancy.

[0024] The average diameter of the carbon nanotubes can be measured, for example, by the following method. First, the expanded beads are cut into approximately two equal halves along the AA cross section shown in Figure 1, and the cut surface is photographed using a scanning electron microscope to obtain an image of the cut surface of the expanded beads. The diameters of the carbon nanotubes present in this image of the cut surface are measured at 50 randomly selected points. The average value of the obtained diameters can then be used as the average diameter.

[0025] The average length of the carbon nanotubes can be measured, for example, by the following method. First, as in the measurement of the average diameter of the carbon nanotubes, a cross-sectional image of the expanded beads is obtained using a scanning electron microscope. 50 carbon nanotubes are randomly selected from the obtained cross-sectional image, and the length of each carbon nanotube is measured by image analysis. If the carbon nanotubes are not linear but have a bent shape, the length along the shape of the carbon nanotube can be measured using a chirvimeter or the like. The average value of the lengths obtained in this manner can be used as the average length.

[0026] (Conductive carbon material content 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. From the viewpoint of achieving 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, from the viewpoint of low 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] (Conductive carbon material content in coating layer) The content (Xo) of the conductive carbon material in the coating layer is 3% by mass or less (including 0). From the viewpoint of improving the foamability 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. The coating layer may not contain the conductive carbon material. In the present invention, it is a condition that 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 auxiliaries) The flame retardant used in the expanded beads of the present invention is preferably a halogen-based flame retardant such as a bromine-based flame retardant or a chlorine-based flame retardant, since it exhibits high flame retardancy. Among these, a bromine-based flame retardant is preferably used, since high flame retardancy can be easily obtained with a small amount of addition.

[0029] Examples of brominated flame retardants include brominated epoxy resins obtained by adding bromine to epoxy resins, brominated aromatic compounds such as hexabromobenzene, pentabromotoluene, ethylenebispentabromodiphenyl, decabromodiphenyloxide, 2,3-dibromopropylpentabromophenyloxide, polybromophenylindane, polypentabromobenzyl acrylate, brominated styrene-butadiene-styrene, brominated polyphenylene ether, and brominated polystyrene, and derivatives thereof; bromine- and nitrogen-containing compounds such as ethylenebis(tetrabromophthal)imide, tris(tribromophenoxy)triazine, and tris(2,3-dibromopropyl)isocyanurate; and tetrabromocyclohexane. brominated bisphenols A and derivatives thereof, such as tetrabromobisphenol A, tetrabromobisphenol A bis(2-bromoethyl) ether, and tetrabromobisphenol A diallyl ether; brominated bisphenols S and derivatives thereof, such as tetrabromobisphenol S and tetrabromobisphenol S(2-bromoethyl) ether; brominated bisphenol derivative oligomers, such as tetrabromobisphenol A polycarbonate oligomer and tetrabromobisphenol epoxy oligomer; and halogen-containing phosphorus compounds, such as tris(tribromoneopentyl)phosphate and tris(bromophenyl)phosphate.

[0030] In particular, tetrabromobisphenol A bis(2,3-dibromopropyl ether) and bis[3,5-dibromo-4-(2,3-dibromopropoxy)phenyl]sulfone are preferred because they exhibit high flame retardancy even when added in small amounts.

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

[0032] The 5% decomposition temperature of the flame retardant is preferably in the range of 260 to 340°C. By having the 5% decomposition temperature of the flame retardant in this range, the brominated flame retardant can exhibit sufficient flame retardant effect in the temperature range where the thermal decomposition of the resin progresses. From the same perspective, the 5% decomposition temperature of the flame retardant is preferably 270 to 320°C, more preferably 285 to 305°C. The 5% decomposition temperature of the flame retardant can be measured using a simultaneous thermogravimetry and differential thermal analyzer (TG / DTA). Specifically, a differential thermal loss curve is measured under the following measurement conditions: a heating rate of 10°C / min, a measurement temperature range of 40 to 500°C, a nitrogen atmosphere, a sample pan made of Pt, and a sample mass of 10 mg. The 5% decomposition temperature can be determined as the temperature at which the weight in the differential thermal loss curve decreases by 5%.

[0033] In the present invention, a flame retardant aid can be added together with the flame retardant. Examples of the flame retardant aid include metal hydroxides, silicone compounds, Teflon, montmorillonite, metal oxides, triazine compounds, and guanidine compounds. Among these, metal oxides are preferred because they provide a synergistic effect when used in combination with a bromine-based flame retardant.

[0034] Examples of metal oxides include zinc borate, zinc stannate, antimony trioxide, antimony pentoxide, etc. Among these, antimony trioxide and zinc stannate are preferably used because they exert a sufficient effect even when added in small amounts.

[0035] (Flame retardant and flame retardant aid content in core layer) The content (Yi) of the flame retardant in the core layer is preferably 1% by mass or more, more preferably 2% by mass or more, even more preferably 3% by mass or more, and even more preferably 4% by mass or more. 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 aid in the core layer is preferably 0.5% by mass or more, more preferably 1% by mass or more, even more preferably 1.5% by mass or more, and even more preferably 2% by mass or more. The content of the flame retardant aid 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 content of the flame retardant and flame retardant aid within the above ranges, it is possible to impart high flame retardancy while imparting more advanced functionality to the expanded beads.

[0037] (Flame retardant and flame retardant auxiliary content in coating layer) The content (Yo) of the flame retardant in the coating layer is in the range of 5% by mass or more and 25% by mass or less. From the viewpoint of imparting high flame retardancy, the content (Yo) of the flame retardant in the coating layer is preferably 6% by mass or more, more preferably 6.5% by mass or more, and even more preferably 7% by mass or more. On the other hand, from the viewpoint of secondary foaming, the content (Yo) of the flame retardant 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] The content of the flame retardant aid in the coating layer is preferably 2.5% by mass or more, more preferably 3% by mass or more, and even more preferably 3.5% by mass or more, from the viewpoint of imparting high flame retardancy. The content of the flame retardant aid 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, from the viewpoint of secondary foaming.

[0039] The content of the flame retardant in the coating layer (Yo) is preferably greater than the content of the flame retardant in the core layer (Yi). By satisfying the above-mentioned relationship regarding the content of the flame retardant, excellent flame retardancy can be easily ensured, which is preferable.

[0040] (Other additives, etc.) The coating layer and the core layer of the expanded thermoplastic resin beads of the present invention may contain additives as needed. Examples of these additives include antioxidants, UV inhibitors, pigments, dyes, nucleating agents, lubricants, and affinity agents. The additives may be used to the extent that they do not impair 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 expanded thermoplastic resin beads of the present invention, the mass ratio of coating layer to core layer is 99:1 to 50:50. By setting the mass ratio of coating layer to core layer within this range, the core layer, which contains a large amount of conductive carbon material, is reliably coated with the coating layer, the coating layer becomes expandable, and secondary expandability is also ensured. This makes it possible to obtain expanded beads that contain a large amount of conductive carbon material and have excellent fusion properties during molding and dimensional stability of the molded product. From this perspective, the mass ratio is preferably 99:1 to 60:40, more preferably 99:1 to 80:20, and even more preferably 95:5 to 90:10. Note that the mass in this mass ratio includes the mass of the thermoplastic resin and the conductive carbon material contained in the thermoplastic resin.

[0042] In the expanded beads of the present invention, the core layer may be completely covered with the coating layer, or a part of the core layer may be exposed. An example of a structure in which the core layer is exposed is a structure in which only the side surfaces of a cylindrical core layer are covered with the coating layer, and the core layer is exposed on the top and / or bottom surfaces of the cylinder.

[0043] [Functions of thermoplastic resin foam particles] In the expanded thermoplastic resin beads of the present invention, the core layer contains a conductive carbon material and a flame retardant, and the ratio (Yi / Xi) of the content of the flame retardant (Yi) in the core layer to the content (Xi) of the conductive carbon material in the core layer is 0.2 or more. By setting the compounding ratio (Yi / Xi) of the content (Xi) of the conductive carbon material and the content (Yi) of the flame retardant in the core layer within the above range, flame retardancy can be imparted while still containing the conductive carbon material. From this perspective, the compounding ratio (Yi / Xi) is preferably 0.3 or more, more preferably 0.4 or more. Meanwhile, the compounding ratio (Yi / Xi) is preferably 10 or less, more preferably 5 or less, and even more preferably 1 or less.

[0044] In addition, the expanded beads of the present invention may be configured to have, in addition to the core layer and the coating layer, other layers, such as an outermost layer, or layers formed between the core layer and the coating layer, as long as the effects of the present invention are not impaired.

[0045] According to the expanded beads of the present invention having the above-mentioned conditions, even if the expanded beads as a whole contain a large amount of conductive carbon material and flame retardant, the secondary expandability of the expanded thermoplastic resin beads is not inhibited, and the fusion properties of the expanded bead molded article can be maintained. Therefore, even without performing operations such as increasing the molding pressure or pre-pressurizing the expanded beads when molding the expanded beads, it is possible to obtain an expanded bead molded article that contains a large amount of conductive carbon material and flame retardant, has a high fusion rate, excellent secondary expandability, and suppressed shrinkage. Furthermore, since the conductive carbon material and flame retardant can be prepared in various types and amounts in the expanded thermoplastic resin beads, expanded bead molded articles with various functionalities can be obtained.

[0046] [Method of manufacturing thermoplastic resin foam beads] The expanded resin 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 a core layer is kneaded in one extruder, and a thermoplastic resin composition for forming a coating layer is kneaded in the other extruder. The resulting mixture is then co-extruded through a die of a predetermined shape to obtain a sheath-core string-like composite consisting of a core layer and a coating layer that coats the core layer. Next, the co-extruded string-like composite is cut to a predetermined mass or size using a cutting machine equipped with a take-up device, thereby obtaining columnar composite resin particles consisting of a core layer and a coating layer.

[0047] Expanded resin beads can be produced by conventionally known methods, such as extrusion-type expanded bead production, methods in which expandable resin beads containing a blowing agent are released from a pressurizable sealed container to expand, and methods in which expandable resin beads containing a blowing agent are heated and softened to expand. Among these methods, the expanded beads of the present invention are preferably obtained by dispersing composite resin beads consisting of a core layer and a coating layer in an aqueous medium (usually water) in a pressurizable sealed container (e.g., an autoclave), adding a dispersant, injecting a required amount of blowing agent under pressure, and stirring under heat for a required time to impregnate the composite resin beads with the blowing agent. The contents are then released together with the aqueous medium to a pressure range lower than the pressure inside the container, thereby expanding the expanded beads. The method of releasing expandable resin beads containing a blowing agent from a sealed container to expand the beads is preferred because it facilitates achieving the average cell diameters of the coating layer and foam layer of the resulting expanded beads within the preferred ranges described below.

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

[0049] Examples of dispersants that can be used include inorganic substances that are poorly soluble in water, such as aluminum oxide, tricalcium phosphate, magnesium pyrophosphate, zinc oxide, kaolin, and mica, and water-soluble polymeric protective colloids, such as polyvinylpyrrolidone, polyvinyl alcohol, and methyl cellulose. Additionally, anionic surfactants, such as sodium dodecylbenzenesulfonate and sodium alkanesulfonate, can be used.

[0050] (Apparent density) The apparent density of the expanded beads of the present invention is 25 to 150 kg / m 3 By setting the apparent density of the expanded beads in the above range, it is possible to obtain excellent lightness and moldability. From this viewpoint, the apparent density is preferably 30 to 125 kg / m 3 More preferably, 35 to 100 kg / m 3 is more preferable.

[0051] The apparent density of the expanded particles was measured by preparing a measuring cylinder filled with water at 23°C, submerging the expanded particles (weight W [g] of the expanded particles) in the measuring cylinder using a wire mesh or the like, and calculating the volume V [cm] of the expanded particles from the rise in the water level. 3 ] was calculated, and the weight of the expanded particle group was divided by the volume of the expanded particle group (W / V), and then [kg / m 3 ] can be calculated by converting the unit to

[0052] (closed cell ratio) From the viewpoint of foam moldability, the closed cell ratio of the expanded beads is preferably 80% or more, more preferably 85% or more, and even more preferably 90% or more. The closed cell ratio of the expanded beads can be determined by the following procedure: Expanded beads are left in a temperature-controlled room for 10 days or more as a measurement sample, and the apparent volume Va is accurately measured using a method for measuring the apparent density of the expanded beads (submersion method). After measuring the apparent volume Va, the measurement sample is thoroughly dried, and the true volume Vx of the measurement sample is measured using an air comparison hydrometer such as the "Air Comparison Hydrometer 930" manufactured by Toshiba Beckman Corporation, in accordance with Procedure C described in ASTM-D2856-70. Based on these volume values ​​Va and Vx, the closed cell ratio is calculated using the following formula, and the average value of five samples (N=5) is taken as the closed cell ratio of the expanded beads. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) however, Vx: The true volume of the expanded beads measured by the above method, i.e., the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells in the expanded beads (cm 3 ) Va: The apparent volume (cm) of the foamed particles measured by submerging them in a measuring cylinder containing water and measuring the rise in the water level. 3 ) W: Weight of the sample for measuring foam particles (g) ρ: Density of the resin that makes up the foamed particles (g / cm 3 )

[0053] (average bubble diameter in coating layer) In the expanded beads of the present invention, the average cell diameter of the coating layer is preferably 50 μm or more and 300 μm or less. From the viewpoint of obtaining an expanded bead molding with excellent secondary expandability and a small shrinkage rate, the average cell diameter of the coating layer is more preferably 55 μm or more and 250 μm or less, and even more preferably 60 μm or more and 200 μm or less.

[0054] The core layer may be a foamed core layer or a substantially non-foamed core layer. From the viewpoint of easily achieving excellent capacitance, the core layer is preferably a foamed core layer. When the core layer is foamed, the average bubble diameter of the core layer is preferably smaller than the average bubble diameter 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 bubble diameter of the core layer is preferably 5 μm or more. When the average bubble diameter of the core layer satisfies the above range, excellent capacitance is more easily achieved. Note that "substantially non-foamed" refers not only to a core layer in which no bubbles are present (including bubbles that were formed during foaming of the expanded beads but have since melted and been destroyed, resulting in the disappearance of the bubbles), but also to a core layer in which only a small number of extremely small bubbles are present. When the core layer is foamed, 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, more preferably 2 to 5.

[0055] The average cell diameter of the coating layer and core layer can be determined as follows based on a magnified microscopic photograph of an expanded bead cut approximately in half along the AA cross section shown in Figure 1. First, in the magnified photograph of the cut surface of the expanded bead, a perpendicular bisector l is drawn to the line segment that is the shortest distance from the top surface to the bottom surface, passing through the center of the cut surface of the expanded bead. The length of the line l from the left surface to the right surface of the expanded bead through which l passes is measured and defined as Lc (μm). The number of bubbles Nc (cells) intersecting with the line l is determined, and the value Lc / Nc obtained by dividing Ls by N is used as the average cell diameter of the core layer of one expanded bead. A curve passing 100 μm inward from the top surface is drawn from the right surface to the left surface, and the length Ls (μm) and the number Ns (cells) of bubbles intersecting with the curve are determined. The value Ls / Ns obtained by dividing Ls by Ns is used as the average cell diameter of the coating layer of one expanded bead.

[0056] Furthermore, the core layer preferably has a higher density than the coating layer, which will be described later. The following method can be used to confirm that the core layer has a higher density than the coating layer. For 20 or more randomly selected expanded beads, the expanded beads are cut into three equal parts at equal intervals, A, B, and C, as shown in Figure 2. Then, A+C are designated as expanded bead pieces I and B as expanded bead pieces II, and the apparent densities of each are determined using the same method as for the apparent density of expanded beads, which will be described later. From these apparent density results, the apparent density ratio (expanded bead pieces II / expanded bead pieces I) is determined. When the apparent density ratio (expanded bead pieces II / expanded bead pieces I) is greater than 1, the core layer can be considered to have a higher density than the coating layer. The apparent density ratio (expanded bead pieces II / expanded bead pieces I) is preferably greater than 1.0, more preferably 1.1 or greater, and even more preferably 1.2 or greater.

[0057] (heat of fusion at 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 of the high-temperature peak (high-temperature peak calorific value) of the secondary crystals as determined by differential thermal analysis is preferably 1 to 30 J / g. Specifically, when 2 to 10 mg of the expanded polyolefin resin beads are heated from 23°C to 220°C at a heating rate of 10°C / min by heat flux differential scanning calorimetry, the DSC curve (DSC curve of the first heating) preferably has an endothermic peak A (intrinsic peak) having a peak temperature inherent to the polyolefin resin, and one or more endothermic peaks B (high-temperature peaks) derived from the secondary crystals, each having a peak temperature in the temperature range higher than the intrinsic peak. Furthermore, the high-temperature peak calorific value is preferably 1 to 30 J / g, more preferably 5 to 20 J / g. By having the high-temperature peak calorific value within the above range, expanded bead moldings with excellent molding fusion properties can be obtained. The high-temperature peak calorific value corresponds to the area of ​​the high-temperature peak, and can be determined specifically as follows. First, a line (α-β) is drawn connecting point α on the DSC curve, which corresponds to 80°C, and point β on the DSC curve, which corresponds to the melting end temperature T of the expanded beads. The melting end temperature T is the temperature corresponding to the intersection of the DSC curve on the high-temperature side of high-temperature peak B and the high-temperature-side baseline. Next, a line parallel to the vertical axis of the graph is drawn from point γ on the DSC curve, which corresponds to the valley between intrinsic peak A and high-temperature peak B, and the point where it intersects with the line (α-β) is designated as σ. The area of ​​high-temperature peak B is the area enclosed by the curve of high-temperature peak B on the DSC curve, the line segment (σ-β), and the line segment (γ-σ), and this corresponds to the heat quantity of the high-temperature peak. The high-temperature peak B appears in the DSC curve of the expanded beads measured in the first heating as described above, but does not appear in the DSC curve of the second heating, which is obtained by cooling the expanded beads from 200°C to 25°C at a cooling rate of 10°C / min after obtaining the DSC curve of the first heating and then heating them again to 200°C at a heating rate of 10°C / min.Instead, only an endothermic peak similar to the intrinsic peak A appears in the DSC curve of the second heating.Therefore, the intrinsic peak A and the high-temperature peak B can be easily distinguished.

[0058] Expanded beads having a high-temperature peak in the DSC curve can be obtained by a method in which, during the expanded bead production process, the temperature is not raised above the melting end temperature (T) of the polyolefin resin during heating, but is stopped at an arbitrary temperature (Ta) in the range of at least 20°C lower than the melting point (Tm) of the polyolefin resin and lower than the melting end temperature (T), and the temperature (Ta) is maintained for a sufficient time, preferably for about 10 to 60 minutes (first-stage maintenance step), and then the temperature is adjusted to an arbitrary temperature (Tb) in the range of from a temperature 15°C lower than the melting point (Tm) to the melting end temperature (T) + 10°C, and if necessary, the temperature is maintained for a further sufficient time, preferably for about 10 to 60 minutes (second-stage maintenance step), after which the expandable resin beads are released from the sealed container under low pressure and expanded.

[0059] [Thermoplastic resin foamed particle molding] The expanded bead moldings of the present invention can be produced by molding only the expanded beads of the present invention in a mold, or by molding a mixture of the expanded beads of the present invention and other commonly known expanded beads of thermoplastic resins. The size and shape of the expanded bead moldings are not particularly limited, and they can be formed into various three-dimensional shapes such as plates, columns, polygonal pyramids, and cones.

[0060] [Method for molding a thermoplastic resin foamed bead molded product] The expanded bead molding can be produced, for example, by an in-mold molding method. Specifically, a mold designed to the desired shape is first prepared. Next, the expanded beads of the present invention are filled into the mold, and steam is supplied into the mold to heat it. At this time, the coating layers of adjacent expanded beads fuse together, and the thermoplastic resin expanded beads undergo secondary expansion to fill the gaps between the expanded beads, and the numerous thermoplastic resin expanded beads filled in the mold are integrated. The mold is then cooled, and the contents are removed from the mold to obtain the expanded bead molding.

[0061] (Molded body density) The foamed bead molding of the present invention is not particularly limited in density, but is usually 9 to 300 kg / m 3The density of the molded article can be determined by dividing the mass of the molded article by the volume of the molded article. The volume of the expanded bead molded article can be determined from the outer dimensions of the molded article.

[0062] (Fusion rate) When considering the production of expanded bead moldings with excellent dimensional stability and appearance, it is desirable that the fusion rate of the expanded beads that make up the expanded bead moldings be 70% or more, preferably 80% or more, and more preferably 90% or more.

[0063] The expanded bead molding of the present invention preferably has a capacitance of 0.12 to 0.4 pF, more preferably 0.2 to 0.35 pF. When the capacitance of the expanded bead molding satisfies the above range, excellent radio wave absorbing performance can be expected, and the molding can be suitable as a radio wave absorbing material. [Example]

[0064] The present invention will be described in more detail below with reference to examples.

[0065] A raw master batch (MB) was prepared using the following raw materials, and expanded thermoplastic resin beads of Examples 1 to 10 shown in Table 5 and Comparative Examples 1 to 5 shown in Table 6 were obtained. (raw materials) The following thermoplastic resins, conductive carbon materials, flame retardants, and flame retardant assistants were used as raw materials. Thermoplastic resin: Polypropylene resin shown in Table 1 Conductive carbon materials: Conductive carbon materials shown in Tables 2 and 3 Flame retardants and flame retardant auxiliaries: Flame retardants and flame retardant auxiliaries 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 resins shown in Table 1, the conductive carbon materials shown in Tables 2 and 3, and the flame retardants and flame retardant auxiliaries shown in Table 4 were each supplied to a twin-screw extruder having an inner diameter of 20 mm in the blending ratios shown in Tables 5 and 6 below, melt-kneaded at 150 to 190°C, and extruded into strands. The strands were cooled and cut to obtain masterbatches for forming the core layer and coating layer of Examples 1 to 10 and Comparative Examples 1, 2, 4, and 5, and a masterbatch for forming the core layer of Comparative Example 3.

[0071] [Production of thermoplastic resin particles (resin particles)] Example 1 Using a single-layer extruder (25 mm inner diameter) for the resin particle core layer and a twin-screw extruder (26 mm inner diameter) for the resin particle coating layer, each equipped with a multilayer strand forming die at the outlet, the masterbatch for forming the core layer was fed to the extruder (25 mm inner diameter) for the resin particle core layer, and the masterbatch for forming the coating layer was fed to the extruder (26 mm inner diameter) for the resin particle coating layer, so as to obtain the formulation shown in Table 5. Each was heated to a set temperature of 190-210°C, melted, kneaded, and then fed to the die. The resulting mixtures were then merged in the die and coextruded through the holes in the nozzle attached to the tip of the extruder as a multilayer strand with the coating layer coated on the side of the core layer. The coextruded strand was then water-cooled and cut into 2 mg pieces with an L / D ratio of 2.4 using a pelletizer to obtain cylindrical resin particles formed into two layers (sheath-core structure) as shown in Table 5. The coating layer was supplied with zinc borate as a cell adjusting agent so that the content was 1000 ppm by mass, and the mass ratio of the core layer to the coating layer was 7:93.

[0072] [Production of expanded thermoplastic resin beads (expanded beads)] 1 kg of the resin particles was placed in a 5-L autoclave together with 3 L of water as a dispersion medium, and 3 g of kaolin as a dispersant, 0.04 g of sodium alkylbenzenesulfonate as a dispersion aid, and 0.1 g of aluminum sulfate were added to the dispersion medium. Carbon dioxide as a blowing agent was injected into a sealed container to the pressure inside the sealed container shown in Table 5. The mixture was heated to the foaming temperature with stirring and maintained at that temperature for 15 minutes to adjust the high-temperature peak heat quantity. After that, the contents of the autoclave were released together with water under atmospheric pressure to obtain expanded particles.

[0073] [Production of expanded thermoplastic resin bead molded products] The foamed beads obtained above were filled into the cavity of a flat mold measuring 250 mm (long side) x 200 mm x 50 mm thick, and molded in-mold using steam heating to obtain a foamed molded plate. The heating method involved preheating (exhaust step) by supplying steam for 5 seconds with the drain valves on both sides of the mold open, followed by one-way heating at a pressure 0.04 MPa (G) lower than the main heating pressure, followed by one-way heating from the opposite direction at a pressure 0.02 MPa (G) lower than the main heating pressure, and then heating at the molding heating steam pressure (molding pressure) shown in Table 5. (G) indicates gauge pressure.

[0074] The molding pressure indicates the minimum pressure at which a molded product with excellent appearance can be obtained without significant shrinkage. After heating, the pressure was released and the molded product was water-cooled until the surface pressure due to the expansion force of the molded product reached 0.04 MPa (G). The mold was then opened and the molded product was removed from the mold. The obtained molded product was cured in an oven at 80°C for 12 hours to obtain an expanded bead molded product. The physical properties of the obtained expanded bead molded product are shown in Table 5.

[0075] Examples 2 to 10 Resin beads, expanded beads, and expanded bead moldings were obtained in the same manner as in Example 1, except that the production conditions were as shown in Table 5.

[0076] (Comparative Examples 1 to 5) In Comparative Examples 1, 2, 4, and 5, resin beads, expanded beads, and expanded bead moldings were obtained in the same manner as in Example 1, except that the production conditions were as shown in Table 6. In Comparative Example 3, only the masterbatch for forming the core layer was produced to the composition shown in Table 6. This was fed into an extruder for forming the resin bead core layer with an inner diameter of 25 mm, heated to a set temperature of 190 to 210°C, melted, and kneaded, and then extruded as a single-layer strand through the holes in the nozzle attached to the tip of the extruder. The single-layer strand was then water-cooled and cut into 2 mg pieces with a pelletizer and an L / D ratio of 2.4 to obtain the cylindrical resin beads formed into a single layer as shown in Table 6. The same procedures as in Example 1 were then used to obtain an expanded bead molding.

[0077] In Tables 5 and 6, coating layer / core layer (mass ratio) indicates the mass ratio (%) of the coating layer and the core layer to the total mass of the particle. The extrusion processability of each resin particle was evaluated according to the following criteria, and the results are shown in Tables 5 and 6. ○: No surging occurred during extrusion (no slight fluctuations in discharge for each strand), and the strand thickness was always consistent △: Slight surging occurred during extrusion (there was a slight variation in discharge for each strand), and the thickness of the strand changed slightly.

[0078] The physical properties of the expanded beads and the expanded bead moldings of Examples 1 to 10 and Comparative Examples 1 to 5 were measured and evaluated by the following methods. The results are shown in Tables 5 and 6. (Apparent density of expanded particles) The apparent density of the expanded particles was determined by the following procedure: First, a measuring cylinder filled with water at 23°C was prepared, and the expanded particles (weight W [g] of the expanded particles) were submerged in the measuring cylinder using a wire mesh. The volume V [cm] of the expanded particles was calculated from the rise in the water level. 3 ] was calculated, and the weight of the expanded particle group was divided by the volume of the expanded particle group (W / V), and then [kg / m 3 ] was calculated by converting the units.

[0079] (Apparent density ratio) The apparent density ratio was measured by the following method. First, 20 randomly selected expanded beads were cut into three equal parts A, B, and C at equal intervals as shown in Figure 2. Then, A + C were designated as expanded bead piece I, and B was designated as expanded bead piece II, and the apparent density of each was determined by the same method as for the apparent density of the expanded beads. Furthermore, the apparent density ratio (expanded bead piece II / expanded bead piece I) was calculated from these apparent density results.

[0080] (Closed cell ratio of foamed particles) The closed cell ratio of the expanded beads was measured by the following procedure: After leaving the expanded beads in a constant temperature room for 10 days, the bulk volume was approximately 20 cm 3 The expanded beads were used as measurement samples, and the apparent volume Va was accurately measured using the measurement method for the apparent density of the expanded beads (submersion method). After measuring the apparent volume Va, the measurement sample was thoroughly dried, and the true volume Vx of the measurement sample was measured using an air comparison hydrometer 930 manufactured by Toshiba Beckman Corporation in accordance with Procedure C described in ASTM-D2856-70. Based on these volume values ​​Va and Vx, the closed cell ratio was calculated using the following formula, and the average value of five samples (N=5) was taken as the closed cell ratio of the expanded beads. Closed cell ratio (%)=(Vx-W / ρ)×100 / (Va-W / ρ) however, Vx: The true volume of the expanded beads measured by the above method, i.e., the sum of the volume of the resin constituting the expanded beads and the total volume of the closed cells in the expanded beads (cm 3 ) Va: The apparent volume (cm) of the foamed particles measured by submerging them in a measuring cylinder containing water and measuring the rise in the water level. 3 ) W: Weight of the sample for measuring foam particles (g) ρ: Density of the resin that makes up the foamed particles (g / cm 3 )

[0081] (Average bubble diameter of coating layer and core layer) The average cell diameters of the coating layer and core layer were measured as follows. An expanded bead was roughly bisected along the AA cross section shown in Figure 1, and the cut surface was photographed under a microscope. The average cell diameter was determined as follows: First, in the magnified photograph of the cut surface of the expanded bead, a perpendicular bisector l was drawn to the line segment that was the shortest distance from the top surface to the bottom surface, passing through the center of the cut surface of the expanded bead. The length of the line l from the left surface to the right surface of the expanded bead through which l passed was measured and defined as Lc (μm). The number of cells Nc (cells) intersected by the line l was calculated, and the value Lc / Nc obtained by dividing Ls by N was used as the average cell diameter of the core layer of one expanded bead. A curve passing 100 μm inward from the top surface was drawn from the right surface to the left surface, and its length Ls (μm) and the number of bubbles Ns (cells) intersecting the curve were determined. Ls was divided by Ns (Ls / Ns), which was taken as the average bubble diameter in the coating layer of one expanded bead. This procedure was performed for 10 expanded beads, and the arithmetic mean of the average bubble diameters in the core layer and coating layer of each expanded bead was taken as the average bubble diameter in the core layer and coating layer of the expanded beads. In Comparative Example 3, only the average bubble diameter in the core layer was determined.

[0082] (High-temperature peak heat value of foamed beads) The calorific value of the high-temperature peak of the expanded beads was measured by the following procedure. In the DSC curve (DSC curve of the first heating) obtained when 1 to 3 mg of expanded beads were heated from 25°C to 200°C at a heating rate of 10°C / min using a heat flux differential scanning calorimeter, an endothermic peak A (intrinsic peak) having a peak temperature inherent to the thermoplastic resin and one or more endothermic peaks B (high-temperature peaks) having peak temperatures in the temperature range higher than the intrinsic peak appeared. The high-temperature peak calorific value was calculated by the method described in the specification. The average value of five randomly selected samples (N=5) was taken as the high-temperature peak calorific value of the expanded beads.

[0083] (Fusion rate of foamed bead molded body) The fusion rate was measured based on the ratio of foamed beads that were broken to the foamed beads exposed on the fracture surface when the foamed bead molding was broken (fusion rate). Specifically, test pieces were cut out from the foamed bead molding, and approximately 5 mm incisions were made in each test piece with a utility knife. The foamed bead molding was then broken along the incisions. Next, the number of foamed beads (n) present on the fracture surface of the foamed bead molding and the number of foamed beads that were broken (b) were measured, and the ratio (b / n) of (b) to (n) was expressed as a percentage to determine the fusion rate (%).

[0084] (Density of foamed bead molding) The density of the expanded bead molding (molded density) is calculated by multiplying the mass (kg) of the molding by the volume (m 3 ) was calculated by dividing by

[0085] (shrinkage rate) The shrinkage percentage [%] of the expanded bead molding was calculated by (250 [mm] - long side length [mm] of the molding) / 250 [mm] × 100. Note that "250 [mm]" refers to the long side dimension of the molding die, and "long side length [mm] of the molding" refers to the long side length of the expanded bead molding obtained in Examples and Comparative Examples, which was measured after curing in an atmosphere at 80°C for 12 hours, followed by slow cooling and further curing in an atmosphere at 23°C for 6 hours.

[0086] (Secondary foaming) The secondary foaming property of the molded article was evaluated as follows. ○: The gaps between the foam particles on the surface of the molded product are completely filled △: Some gaps between the foam particles are observed on the surface of the molded product. ×: The gaps between the foam particles on the surface of the molded article are clearly not filled.

[0087] (Flame retardant) A rectangular parallelepiped specimen measuring 150 mm long, 50 mm wide, and 13 mm thick was cut from approximately the center of the foamed bead molding in the thickness direction as a test specimen for the HBF test of the flame retardancy standard UL94 (prepared with the molded skin layer remaining on one side of the 150 mm long x 50 mm wide specimen). The obtained test specimen was placed with the molded skin layer facing downwards and subjected to the HBF test of the flame retardancy standard UL94, and the flame retardancy was evaluated according to the following evaluation criteria. ○: All five test pieces satisfied the burning rate of 40 mm / min or less between the 100 mm gauge lines, the burning distance of less than 125 mm, or both. ×: One or more of the five test pieces satisfied the burning rate of more than 40 mm / min between the 100 mm gauge lines, the burning distance of 125 mm or more, or both.

[0088] (capacitance) The capacitance of the foamed bead moldings was measured using a capacitance measuring instrument CM113N manufactured by Yamamoto Electric Instruments Co., Ltd. The probe (A1407-8065) ​​used had a detection electrode diameter of 98 mm, a guard electrode outer diameter of 150 mm, an inner diameter of 100 mm, an electrode width of 50 mm, and an insulation distance between the electrodes of 2 mm. First, a metal plate to serve as the counter electrode was placed on a horizontal surface, and a blank molded body with a density of 30 kg / m and no conductive agent, measuring 300 mm long x 300 mm wide x 200 mm thick, was placed on top of it. 3 The expanded polypropylene resin bead molding was placed on top of the expanded polypropylene resin bead molding, and the measurement probe was placed on top of the expanded polypropylene resin bead molding so that there was no gap between the expanded polypropylene resin bead molding and the guard electrode of the measurement probe. After the placement, the capacitance was measured and the origin was adjusted. Thereafter, the measurement probe was placed on each expanded polypropylene resin bead molding (length 250 mm × width 200 mm × thickness 50 mm) obtained in the examples and comparative examples, and the capacitance of the expanded polypropylene resin bead molding was measured.

[0089] (pollution) The staining properties of the foamed bead moldings were evaluated by the degree of staining on fabric. The fabric staining test was performed as follows: A 10 mm wide x 300 mm long x 5 mm thick, uncolored polypropylene rod (A) was fixed on a stand. A 100 mm wide x 200 mm long piece of Kanakin No. 3 cotton white cloth (B) was fixed on top of the rod (A). A 50 mm x 50 mm x 25 mm thick test sample (C) was cut out of the foamed bead molding, leaving one 50 mm x 50 mm area of ​​the molded skin layer. This test sample was placed on the white cloth (B) with the molded skin layer of the foamed bead molding facing downwards, and a 3 kg weight (D) was then placed on top of the white cloth.

[0090] Sample (C) and weight (D) were fixed in a jig and moved back and forth over white cloth (B), and the staining of the cloth was compared as an L* value. The amplitude of the reciprocating motion was 200 mm, the frequency was 4.5 Hz, and the test time was 10 seconds. The white cloth (B) and sample (C) were changed each time, and the test was carried out five times for each type.

[0091] The degree of staining of the fabric was evaluated as follows. The L* value (L*B) of the white fabric was measured before the staining test, and the L* value (L*A) of the stained area of ​​the white fabric was measured after the staining test for each sample obtained in the five tests. The L*AL*B value (ΔL*) was calculated, and the arithmetic mean of each ΔL* was used to determine the degree of staining. The L* value was measured using a spectrophotometer / colorimeter (CM-5, manufactured by Konica Minolta Japan) with a measurement section mesh size of φ8 mm and measurement method: reflection measurement, SCE method.

[0092] [Table 5]

[0093] [Table 6]

[0094] In the foams of Examples 1 to 10, the core layer is highly filled with conductive carbon material, and the coating layer is foamed with a flame retardant. Therefore, it was confirmed that secondary foaming occurs during in-mold molding in the foamed bead molding, resulting in foamed molded articles that contain a large amount of conductive carbon material, have stable capacitance, excellent fusion properties and dimensional stability, as well as excellent flame retardancy and contamination resistance.

[0095] On the other hand, Comparative Example 1 is an example in which carbon black was used as the conductive carbon material, and the capacitance was higher than in the Examples, and detachment of the conductive carbon material was observed, resulting in a high level of contamination. Comparative Example 2 is an example in which the ratio (Yi / Xi) of the content of flame retardant in the core layer (Yi) to the content of conductive carbon material in the core layer (Xi) was lower than the specified value of the present invention, i.e., the content of flame retardant in the core layer (Yi) was too low relative to the content of conductive carbon material (Xi), resulting in poor flame retardancy. Comparative Example 3 is an example in which a single-layer expanded particle having only a core layer was used, resulting in significantly poor secondary expandability and a high level of contamination. Furthermore, Comparative Example 4 is an example in which the core layer was foamed and a conductive carbon material was contained in the coating layer, resulting in significantly poor flame retardancy and a high level of contamination. Furthermore, Comparative Example 5 is an example in which the content of conductive carbon material in the core layer was low, resulting in significantly low capacitance.

Claims

1. A thermoplastic resin foam particle containing a conductive carbon material and a flame retardant, the conductive carbon material is one or more selected from the group consisting of carbon nanotubes, carbon nanofibers, carbon nanostructures, and graphene; the conductive carbon material content (Xi) in the core layer is 1% by mass or more and 30% by mass or less; the conductive carbon material content (Xo) in the coating layer is 3% by mass or less (including 0); the flame retardant content (Yo) in the coating layer is 5% by mass or more and 25% by mass or less; the conductive carbon material content (Xo) in the coating layer is less than the conductive carbon material content (Xi) in the core layer; and 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 more.

2. 2. The expanded thermoplastic resin beads according to claim 1, 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. 2. The expanded thermoplastic resin particles according to claim 1, wherein the conductive carbon material is a carbon nanotube.

4. The apparent density of the expanded thermoplastic resin particles is 25 to 150 kg / m ３ 2. The expanded thermoplastic resin particles according to claim 1, wherein

5. 2. The expanded thermoplastic resin beads according to claim 1, wherein the thermoplastic resin forming the core layer and the thermoplastic resin forming the coating layer are both polyolefin resins.

6. 2. The expanded thermoplastic resin particles according to claim 1, wherein the average cell diameter of the coating layer is 50 μm or more and 300 μm or less.

7. 2. The expanded thermoplastic resin beads according to claim 1, wherein the core layer is an expanded core layer, and the average bubble diameter of the core layer is 5 μm or more and less than 50 μm.

8. 2. The expanded thermoplastic resin beads according to claim 1, wherein the mass ratio of the coating layer to the core layer is 99:1 to 80:

20.

9. A foamed thermoplastic resin bead molding obtained by molding the foamed beads according to any one of claims 1 to 8 in a mold.

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