Powder, electromagnetic wave absorber, and method for producing melt molded body

Abstract

The present invention provides: a powder which is capable of forming an electromagnetic wave absorption layer that has electromagnetic wave absorption characteristics in a wider frequency region than ever before and is suppressed in performance variation, and which can be electrostatically adhered or heat fixed to a support body; and an electromagnetic wave absorber which comprises a melt molded body of the powder as an electromagnetic wave absorption layer. The present invention provides: a powder which is capable of forming an electromagnetic wave absorption layer that has electromagnetic wave absorption characteristics in a wider frequency region than ever before and is suppressed in performance variation, and which can be electrostatically adhered or heat fixed to a support body; and an electromagnetic wave absorber which comprises a melt molded body of the powder as an electromagnetic wave absorption layer.

Description

Methods for producing powder, electromagnetic wave absorber, and melt-molded product

[0001] The present disclosure relates to a powder used in an electromagnetic wave absorber, an electromagnetic wave absorber including a melt-molded product of the powder, and a method for producing a melt-molded product of the powder.

[0002] Conventionally, electromagnetic wave absorbers have been used to prevent malfunctions caused by electromagnetic waves in electronic devices, communication devices, and the like. Meanwhile, in mobile communication systems, faster communication speeds have been achieved by using electromagnetic waves in higher frequency bands. Next-generation communications such as 5G and 6G are expected to enable high-speed, large-capacity information communication by utilizing electromagnetic waves in the GHz band, which are higher in frequency than the electromagnetic waves previously used. In the automotive field, for example, millimeter-wave radar is used for the purposes of autonomous vehicle driving and collision prevention. Millimeter waves are electromagnetic waves in the high-frequency band with wavelengths of 1 to 10 mm and frequencies of 30 to 300 GHz.

[0003] Known electromagnetic wave absorbing materials include carbon-based, metal-carbon-based, and magnetic-based materials. For example, Patent Document 1 discloses a radio wave absorber comprising pre-foamed beads blended with carbon black and / or graphite. Patent Document 2 discloses a method of embedding particles containing a material that absorbs, reflects, or scatters electromagnetic radiation into the surface of a polymer or the like in a desired manner. Furthermore, in recent years, carbon nanotubes (CNTs) have attracted attention as an electromagnetic wave absorbing material in the millimeter wave band due to their high conductivity and relatively light weight. Patent Document 3 discloses a thermoplastic resin composition for radar covers that utilizes the electromagnetic wave properties of carbon nanotubes and carbon black.

[0004] When forming an electromagnetic wave absorbing layer on the surface of various components, it is desirable to make the electromagnetic wave absorbing layer thinner from the viewpoints of cost reduction, miniaturization of equipment, etc., and there is also a need for a means to easily form such an electromagnetic wave absorbing layer. However, electromagnetic wave absorbing layers produced by conventional methods have problems such as an insufficient width of the frequency range in which they can exhibit electromagnetic wave absorption properties and variations in performance.

[0005] Japanese Patent Laid-Open No. 4-44299 Japanese Patent Laid-Open No. 2016-65253 Special Publication No. 2016-504471

[0006] The present disclosure aims to provide a powder that has electromagnetic wave absorption properties over a wider frequency range than conventional powders, can form an electromagnetic wave absorbing layer with reduced performance variation, and can be electrostatically attached and thermally fixed to a support. Another object of the present disclosure is to provide an electromagnetic wave absorber that includes a melt-molded product of the powder as an electromagnetic wave absorbing layer.

[0007] The present inventors have conducted extensive research to achieve the above-mentioned object, and have found that a powder consisting of thermoplastic resin particles having an electrostatic property can be formed into a thin resin layer by electrostatic adhesion to a support and thermal fixation, and that when the particle size of the particles constituting the powder is set within a specific range and further when specific additives are added to only some of the particles, the resin layer formed by melting and solidifying the powder exhibits electromagnetic wave absorption properties in a wide frequency range of 30 to 100 GHz and has excellent uniformity of performance, which has led to the present disclosure.

[0008] That is, the present disclosure provides the following powder: [1] A powder comprising a plurality of particles containing a binder resin and a charge control agent dispersed in the binder resin, wherein the absolute value of the charge amount per unit area of ​​the powder is 40 to 1500 mC / cm ２A powder characterized in that the particles have a volume average particle size of 2 to 100 μm, the binder resin is a thermoplastic resin, and 5 to 95% by number of the particles out of 100% by number of the particles contain additive A, which is at least one selected from the group consisting of carbon nanotubes, carbon nanohorns, and carbon fibers, dispersed in the binder resin, and the remaining particles do not contain additive A. [2] The powder according to [1], wherein additive A is carbon nanotubes. [3] The powder according to [2], wherein carbon nanotubes are single-walled carbon nanotubes. [4] The powder according to any one of [1] to [3], wherein the content of additive A is 0.01 to 2.0 parts by mass per 100 parts by mass of the binder resin. [5] The powder according to any one of [1] to [4], wherein the charge control agent is a polymer compound. [6] The powder according to any one of [1] to [5], wherein the content of additive B, which is at least one selected from the group consisting of amorphous carbon, graphite, graphene, fullerene, metal oxide magnetic material, and metal magnetic material, is less than 12 parts by mass per 100 parts by mass of the binder resin. [7] The powder according to any one of [1] to [6], wherein the average circularity of the particles is 0.94 or more. [8] The powder according to any one of [1] to [7], wherein the binder resin is at least one selected from the group consisting of styrene-acrylic resin, acrylic resin, and polyester resin. [9] The powder according to any one of [1] to [8], wherein the angle of repose of the powder is 15 to 45°.

[0009]

[10] The powder according to any one of [1] to [9], wherein the melting temperature (T1 / 2) of the powder according to the half-method is 110 to 260°C or less.

[11] The powder according to any one of [1] to

[10] , wherein the binder resin further contains a styrene-acrylic resin and a thermoplastic resin different from the styrene-acrylic resin.

[12] The powder according to any one of [1] to

[11] , wherein the binder resin contains a polymer of a polymerizable monomer containing styrene and a (meth)acrylic acid ester, and at least one resin selected from the group consisting of a polycarbonate resin and a polyester resin.

[13] The powder according to any one of [1] to

[12] , wherein the binder resin contains a resin crosslinkable by heat or an electron beam.

[14] The powder according to

[13] , wherein the resin crosslinkable by heat or an electron beam is a polymer of a polymerizable monomer containing styrene, a (meth)acrylic acid ester, and a reactive group-containing monomer.

[15] The powder according to

[14] , wherein the reactive group-containing monomer contains at least one selected from the group consisting of an epoxy group-containing monomer and a hydrolyzable silyl group-containing monomer.

[16] The powder according to

[13] , wherein the resin crosslinkable by heat or electron beam is a polymer of polymerizable monomers containing styrene, a (meth)acrylic acid ester, and a crosslinkable macromonomer.

[17] The powder according to

[16] , wherein the crosslinkable macromonomer is at least one selected from the group consisting of a polymer compound containing polymerizable functional groups at multiple terminals and a polymer compound containing a structure containing a butadiene-derived structural unit.

[18] The powder according to any one of [1] to

[17] , wherein the particles further contain at least one crosslinkable resin selected from the group consisting of a thermosetting resin and an electron beam-curable resin.

[19] The powder according to

[18] , wherein the crosslinkable resin is at least one selected from the group consisting of an epoxy resin and a maleimide resin.

[20] The powder according to any one of [1] to

[19] , wherein the particles further contain a silane coupling agent.

[0010] The present disclosure also provides the following electromagnetic wave absorbers:

[21] An electromagnetic wave absorber comprising, as an electromagnetic wave absorbing layer, a melt-molded product of the powder according to any one of [1] to [9].

[22] An electromagnetic wave absorber comprising, as an electromagnetic wave absorbing layer, a melt-molded product of the powder according to any one of [1] to

[20] .

[0011] The present disclosure also provides the following methods for producing a melt-molded product.

[23] A method for producing a melt-molded product of powder, comprising melting the powder according to any one of [1] to

[20] and cooling the melted powder.

[24] A method for producing a melt-molded product of powder, comprising melting the powder according to any one of

[13] to

[17] , thermally crosslinking the crosslinkable resin contained in the melted powder, and then cooling the melted powder.

[25] A method for producing a melt-molded product of powder, comprising melting the powder according to any one of

[13] to

[17] , cooling the melted powder to obtain a molded product, and then crosslinking the crosslinkable resin contained in the molded product with an electron beam.

[26] A method for producing a melt-molded product of powder, comprising melting the powder according to

[18] or

[19] , thermally crosslinking the crosslinkable resin contained in the melted powder, and then cooling the melted powder.

[27] A method for producing a melt-molded product of the powder, comprising: melting the powder according to

[18] or

[19] , cooling the molten powder to obtain a molded product, and then crosslinking the crosslinkable resin contained in the molded product with an electron beam.

[28] A method for producing a melt-molded product of the powder, comprising melting the powder according to

[20] , crosslinking the silane coupling agent contained in the molten powder with heat, and then cooling the molten powder.

[0012] According to the present disclosure, it is possible to provide a powder that has electromagnetic wave absorption properties over a wider frequency range than conventional powders, that can form an electromagnetic wave absorbing layer with reduced performance variation, and that can be electrostatically attached and thermally fixed to a support. Furthermore, according to the present disclosure, it is possible to provide an electromagnetic wave absorber that includes a melt-molded product of the powder as an electromagnetic wave absorbing layer.

[0013] The powder of the present disclosure will be described in detail below. In this disclosure, the term "to" in a numerical range means that the numerical values ​​before and after the "to" symbol are included as the lower and upper limits. Furthermore, among the numerical values ​​described to explain this disclosure, numerical values ​​that may include decimal places are obtained by rounding off the digit that is one place smaller than the lowest digit included in the numerical value, unless otherwise specified. Furthermore, in this disclosure, a (meth)acrylic monomer refers to a monomer containing at least one selected from the group consisting of an acryloyl group and a methacryloyl group. In this disclosure, (meth)acrylate refers to either acrylate or methacrylate, and (meth)acrylic refers to either acrylic or methacrylic. In this disclosure, improved electromagnetic wave absorption properties refer to a broader frequency range in which electromagnetic wave absorption properties can be exhibited, an increased electromagnetic wave absorption rate, or both.

[0014] 1. Powder The powder disclosed herein is a powder consisting of a plurality of particles containing a binder resin and a charge control agent dispersed in the binder resin, and the absolute value of the charge amount per unit area of ​​the powder is 40 to 1500 mC / cm ２ The particles have a volume average particle size of 2 to 100 μm, the binder resin is a thermoplastic resin, and 5 to 95% by number of the particles out of 100% by number of the particles contain additive A, which is at least one selected from the group consisting of carbon nanotubes, carbon nanohorns, and carbon fibers, in a dispersed state in the binder resin, and the remaining particles do not contain additive A.

[0015] By melt-molding the powder of the present disclosure, an electromagnetic wave absorbing layer provided in an electromagnetic wave absorber, or the electromagnetic wave absorber itself, can be formed. In this specification, the electromagnetic wave absorbing layer formed by melt-molding the powder of the present disclosure may be one provided in an electromagnetic wave absorber, or may be the electromagnetic wave absorber itself. Furthermore, the electromagnetic wave absorbing layer formed by melt-molding the powder of the present disclosure may be one formed by melt-molding the powder of the present disclosure using a known method, or may be one formed by adhering the powder of the present disclosure to the surface of a support and then melt-bonding the powder.

[0016] By melt-molding the powder of the present disclosure, an electromagnetic wave absorbing layer having electromagnetic wave absorption properties over a wider frequency range than conventional ones, such as 30 to 100 GHz, can be formed. This is because, of 100% by number of particles constituting the powder of the present disclosure, 5 to 95% by number of particles contain the specific additive A, while the remaining particles do not contain additive A, and the particles that contain additive A do not contain additive A externally but rather in a state where additive A is dispersed in the binder resin. Note that particles that do not contain additive A do not contain additive A, whether dispersed in the binder resin or externally added. In the powder of the present disclosure, only a portion of the particles contain the specific additive A, and additive A is dispersed in the binder resin of the particles. As a result, in the electromagnetic wave absorbing layer formed by melt-molding the powder of the present disclosure, additive A is scattered, causing diffuse reflection of electromagnetic waves by the additive A, and the presence of regions where additive A is absent creates a maze effect, attenuating the electromagnetic waves and exhibiting electromagnetic wave absorption properties. Furthermore, even if additive A is externally added to some of the particles constituting the powder of the present disclosure, the dispersion state of additive A in the resulting electromagnetic wave absorbing layer is unlikely to produce a maze effect, and such electromagnetic wave absorption characteristics cannot be obtained. Furthermore, by using the powder of the present disclosure, an electromagnetic wave absorbing layer with reduced performance variation can be formed. This is because the volume average particle size of the particles constituting the powder of the present disclosure is within the above-mentioned specific range, and further, each particle constituting the powder of the present disclosure contains a charge control agent, the number ratio of particles containing additive A in the powder of the present disclosure is within the above-mentioned range, and the additive A is dispersed in the binder resin. When the volume average particle size of the particles constituting the powder of the present disclosure is within the above-mentioned specific range, the powder of the present disclosure has good fluidity, the particles are less likely to aggregate, gaps are less likely to form between particles, and the particles are not too heavy, making them easy to move, and therefore the particles are more likely to be uniformly arranged. Subsequently, when the powder of the present disclosure is in a molten state, the charge control agent functions as a dispersant for additive A, making it easier for additive A to be uniformly dispersed. Furthermore, by having the proportion of the number of particles containing additive A within the above range, the amount of additive A is appropriate, and therefore a decrease in dispersibility is suppressed.It should be noted that when additive A is externally added to some of the particles constituting the powder of the present disclosure, the fluidity of the powder is reduced, making it difficult for the particles to be uniformly arranged. In this way, the particles constituting the powder of the present disclosure are likely to be uniformly arranged, and additive A is uniformly dispersed in the molten state, so that an electromagnetic wave absorbing layer is formed with reduced performance variation. Furthermore, the thinner the electromagnetic wave absorbing layer, the more likely it is that performance variation will occur, but by using the powder of the present disclosure, it is possible to sufficiently suppress performance variation even when the electromagnetic wave absorbing layer is made thin.

[0017] Furthermore, the powder of the present disclosure has an absolute value of the charge per unit area within the above-mentioned specific range, and is therefore electrostatically charged. Furthermore, each particle contains a thermoplastic resin as a binder resin, making it a thermoplastic powder. This allows the powder of the present disclosure to be electrostatically attached and thermally fixed to a support. By electrostatically attaching and thermally fixing the powder of the present disclosure, a thin electromagnetic wave absorbing layer can be easily formed on the surface of various components.

[0018] Each particle constituting the powder of the present disclosure contains at least a binder resin and a charge control agent dispersed in the binder resin. The powder of the present disclosure may be composed solely of the above particles, but may also contain unavoidable impurities. When the powder of the present disclosure contains unavoidable impurities, the content of the above particles relative to the total amount (100% by mass) of the powder of the present disclosure is typically 98% by mass or more, may be 99% by mass or more, may be 99.5% by mass or more, or may be 99.9% by mass or more. Furthermore, each particle constituting the powder of the present disclosure is preferably a particle containing a binder resin, a base particle containing at least a charge control agent dispersed in the binder resin, and an external additive attached to the surface of the base particle. The particles constituting the powder of the present disclosure may also consist of the above base particle without containing an external additive. Below, the base particle and external additive contained in each particle constituting the powder of the present disclosure, as well as the properties of the powder of the present disclosure, are described in detail.

[0019] 1-1. Base Particles The base particles used in the present disclosure contain at least a binder resin and a charge control agent dispersed in the binder resin, and some of the particles constituting the powder of the present disclosure further contain an additive A dispersed in the binder resin. Furthermore, the base particles may further contain an additive B described below or other additives, or may have a shell layer, within the scope of the present disclosure.

[0020] <Binder Resin> The binder resin contained in the base particles is not particularly limited as long as it is a thermoplastic resin, but a polymer of a polymerizable monomer described below is preferably used from the viewpoint of excellent dispersibility of additive A when the powder of the present disclosure is melted and improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure.

[0021] (Polymerizable Monomer) In the present disclosure, a polymerizable monomer refers to a monomer having a polymerizable functional group, and the polymerizable monomer is polymerized to form a binder resin. Here, the "polymerizable functional group" is a functional group containing a polymerizable ethylenically unsaturated bond, and is typically a vinyl group, but also includes structures containing butadiene-derived structural units such as a polybutadiene structure and a butadiene skeleton. Note that the vinyl group includes vinyl groups contained in (meth)acryloyl groups, allyl groups, etc. From the viewpoint of reactivity, a compound having a vinyl group is preferably used as the polymerizable monomer. The polymerizable monomer preferably contains a monovinyl monomer as a main component. In other words, a polymer of a polymerizable monomer containing a monovinyl monomer is preferably used as the binder resin.

[0022] Examples of monovinyl monomers include aromatic vinyl monomers such as styrene and styrene derivatives such as vinyltoluene and α-methylstyrene; acrylic acid esters such as methyl acrylate, ethyl acrylate, propyl acrylate, butyl acrylate, 2-ethylhexyl acrylate, and dimethylaminoethyl acrylate; methacrylic acid esters such as methyl methacrylate, ethyl methacrylate, propyl methacrylate, butyl methacrylate, 2-ethylhexyl methacrylate, and dimethylaminoethyl methacrylate; (meth)acrylic monomers such as acrylic acid and methacrylic acid; nitrile compounds such as acrylonitrile and methacrylonitrile; amide compounds such as acrylamide and methacrylamide; olefins such as ethylene, propylene, and butylene; etc. These monovinyl monomers can be used alone or in combination of two or more.

[0023] From the viewpoint of achieving excellent dispersibility of additive A when the powder of the present disclosure is melted, and from the viewpoint of improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, the content of the monovinyl monomer in 100 parts by mass of polymerizable monomer is preferably 50 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 90 parts by mass or more, still more preferably 95 parts by mass or more, and particularly preferably 98 parts by mass or more. Also, from the same viewpoint as above, the total content of the aromatic vinyl monomer and the (meth)acrylic monomer in 100 parts by mass of the total of the monovinyl monomer is preferably 60 parts by mass or more, more preferably 70 parts by mass or more, even more preferably 80 parts by mass or more, still more preferably 90 parts by mass or more, and particularly preferably more than 99.95 parts by mass.

[0024] The use of a macromonomer as part of the polymerizable monomer is preferred in terms of improving the dispersibility of Additive A when the powder of the present disclosure is melted. The macromonomer is a reactive oligomer or polymer having a polymerizable carbon-carbon unsaturated double bond at the end of the molecular chain, typically having a number-average molecular weight of 1,000 to 30,000. Examples of the macromonomer include styrene macromonomer, styrene-acrylonitrile macromonomer, polyacrylic acid ester macromonomer, and polymethacrylic acid ester macromonomer. Among these, at least one selected from the group consisting of polyacrylic acid ester macromonomer and polymethacrylic acid ester macromonomer is preferably used. Examples of the acrylic acid ester used in the polyacrylic acid ester macromonomer include the same acrylic acid ester usable as the monovinyl monomer described above. Examples of the methacrylic acid ester used in the polymethacrylic acid ester macromonomer include the same methacrylic acid ester usable as the monovinyl monomer described above. As the macromonomer, it is preferable to appropriately select and use one that, when incorporated into the polymerizable monomer, results in a binder resin with a higher glass transition temperature (Tg) than when not incorporated. Commercially available macromonomers may be used. Examples of commercially available macromonomers include the macromonomer series AA-6, AS-6, AN-6S, AB-6, and AW-6S manufactured by Toagosei Co., Ltd. These macromonomers may be used alone or in combination of two or more. When the polymerizable monomer contains the macromonomer, the content of the macromonomer is not particularly limited, but is preferably 0.03 to 5 parts by mass, more preferably 0.05 to 2 parts by mass, even more preferably 0.08 to 1.5 parts by mass, and even more preferably 0.1 to 1 part by mass, per 100 parts by mass of the monovinyl monomer.

[0025] Monofunctional or polyfunctional macromonomers can be used as macromonomers. Polyfunctional macromonomers can form crosslinks within the polymer, or can leave polymerizable functional groups unreacted in the polymer. Polymers containing polymerizable functional groups can be crosslinked by heat or electron beam irradiation. Therefore, in this disclosure, polyfunctional macromonomers are referred to as "crosslinkable macromonomers." The number-average molecular weight of the crosslinkable macromonomer is typically 1,000 to 30,000, and may be 1,000 to 100,000 because crosslinks are easily formed and the strength of the electromagnetic wave absorbing layer is easily improved. As the crosslinkable macromonomer, for example, at least one selected from the group consisting of polymeric compounds containing polymerizable functional groups at multiple terminals and polymeric compounds containing a structure containing a butadiene-derived structural unit can be used. Examples of polymeric compounds containing polymerizable functional groups at multiple terminals include tetrafunctional or higher polyester acrylates. Commercially available tetrafunctional or higher polyester acrylates include, for example, EBECRYL 800, 810, 450, 820, 846, 870, 1830, and LEO 10801 manufactured by Daicel Allnex Corporation. Polymeric compounds containing a structure containing a butadiene-derived structural unit include, for example, silane coupling agents containing a structure containing a butadiene-derived structural unit. Commercially available silane coupling agents containing a butadiene-derived structural unit include, for example, polymeric silane coupling agents containing a butadiene skeleton or a polybutadiene structure, such as X-12-1287A, X-12-1267B, and X-12-1267B-ES manufactured by Shin-Etsu Chemical Co., Ltd. Silane coupling agents typically contain hydrolyzable silyl groups, and therefore, by using a silane coupling agent as a polymerizable monomer, a polymer containing a hydrolyzable silyl group can be obtained.

[0026] As the polymerizable monomer, any crosslinkable polymerizable monomer may be used in addition to the monovinyl monomer. A crosslinkable polymerizable monomer refers to a monomer having two or more polymerizable functional groups. A crosslinkable polymerizable monomer can form crosslinks within the polymer by reacting two or more polymerizable functional groups during the polymerization reaction of the polymerizable monomer. The use of a crosslinkable polymerizable monomer is preferred because it enables high-speed, low-temperature fixing when thermally fixing the powder of the present disclosure. Examples of crosslinkable polymerizable monomers include aromatic divinyl compounds such as divinylbenzene, divinylnaphthalene, and derivatives thereof; ester compounds in which two or more carboxylic acids having carbon-carbon double bonds are ester-bonded to alcohols having two or more hydroxyl groups, such as ethylene glycol dimethacrylate and diethylene glycol dimethacrylate; other divinyl compounds such as N,N-divinylaniline and divinyl ether; and compounds having three or more vinyl groups. These crosslinkable polymerizable monomers can be used alone or in combination of two or more. Among these, aromatic divinyl compounds are preferably used as the crosslinkable polymerizable monomer, and divinylbenzene is particularly preferably used, from the viewpoint of reactivity and excellent dispersibility of Additive A when the powder of the present disclosure is melted. When the polymerizable monomer contains the crosslinkable polymerizable monomer, the content of the crosslinkable polymerizable monomer is usually 0.1 to 5 parts by mass, preferably 0.3 to 2 parts by mass, and more preferably 0.5 to 1 part by mass, relative to 100 parts by mass of the monovinyl monomer.

[0027] As the polymer of the polymerizable monomer, at least one selected from the group consisting of styrene-acrylic resins and acrylic resins is preferred, and styrene-acrylic resins are particularly preferred, from the viewpoint of excellent dispersibility of additive A when the powder of the present disclosure is melted and improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure. The polymerizable monomer used in the styrene-acrylic resin or acrylic resin preferably contains at least a monovinyl monomer, and may further contain a macromonomer or a crosslinkable polymerizable monomer.

[0028] In the present disclosure, the styrene-acrylic resin is a polymer of polymerizable monomers including an aromatic vinyl monomer and a (meth)acrylic monomer, and may further be copolymerized with other monomers different from the aromatic vinyl monomer or the (meth)acrylic monomer, as long as the object of the present disclosure is not impaired. The aromatic vinyl monomer and (meth)acrylic monomer used in the styrene-acrylic resin are preferably the above-mentioned monovinyl monomers, but may also be macromonomers or crosslinkable polymerizable monomers.

[0029] The polymerizable monomer used in the styrene-acrylic resin preferably contains, as the monovinyl monomer, an aromatic vinyl monomer and a (meth)acrylic monomer; more preferably, as the monovinyl monomer, an aromatic vinyl monomer and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters; and even more preferably, as the monovinyl monomer, styrene and at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters. In order to achieve excellent dispersibility of Additive A when melting the powder of the present disclosure and to improve the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, the acrylic acid ester used in the styrene-acrylic resin may be an alkyl acrylate ester having an alkyl group having 1 to 12 carbon atoms, an alkyl acrylate ester having an alkyl group having 1 to 8 carbon atoms, or an alkyl acrylate ester having an alkyl group having 1 to 6 carbon atoms; among these, at least one selected from the group consisting of butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate is preferred. From the same viewpoint as above, the methacrylic acid ester used in the styrene-acrylic resin may be an alkyl methacrylate ester having an alkyl group having 1 to 12 carbon atoms, an alkyl methacrylate ester having an alkyl group having 1 to 8 carbon atoms, or an alkyl methacrylate ester having an alkyl group having 1 to 6 carbon atoms, and among these, at least one selected from the group consisting of methyl methacrylate, butyl methacrylate, propyl methacrylate, and 2-ethylhexyl methacrylate is preferred.

[0030] The mass ratio of the aromatic vinyl monomer units to the (meth)acrylic monomer units contained in the styrene-acrylic resin (aromatic vinyl monomer units / (meth)acrylic monomer units) is preferably 0.1 to 0.9, and more preferably 0.2 to 0.8. Here, the aromatic vinyl monomer units and the (meth)acrylic monomer units may be monomer units derived from a monovinyl monomer, a crosslinkable polymerizable monomer, or a macromonomer. The total content of the aromatic vinyl monomer units and the (meth)acrylic monomer units contained in the styrene-acrylic resin is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more.

[0031] In the present disclosure, the styrene-acrylic resin used as the binder resin preferably has a mass ratio of styrene units to (meth)acrylic acid ester units (styrene units / (meth)acrylic acid ester units) of 0.1 to 0.9, and more preferably 0.2 to 0.8, from the viewpoint of improving the dispersibility of Additive A when the powder of the present disclosure is melted. From the same viewpoint, the total content of styrene units and (meth)acrylic acid ester units contained in the styrene-acrylic resin is preferably 90 mass% or more, and more preferably 95 mass% or more.

[0032] In the present disclosure, the styrene-acrylic resin used as the binder resin may be a polymer of a polymerizable monomer containing styrene, a (meth)acrylic acid ester, and a reactive group-containing monomer. The polymer of the polymerizable monomer may form crosslinks within the polymer through the reaction of reactive groups contained in the reactive group-containing monomer, or may be crosslinked by heat or electron beams due to the reactive groups remaining unreacted. By using the powder of the present disclosure containing such a polymer as a binder resin, the polymers contained in the electromagnetic wave absorbing layer can be crosslinked, thereby improving the strength of the electromagnetic wave absorbing layer. The reactive group contained in the reactive group-containing monomer may be a reactive group generated by deprotection.

[0033] The reactive group-containing monomer is appropriately selected so that a covalent bond is formed by a chemical reaction between the reactive groups. Examples of the reactive group include a hydroxyl group, an amino group, an epoxy group, a thiol group, an isocyanate group, a carboxyl group, an acid anhydride group, a sulfonic acid group, a chlorosulfonic acid group, a phosphate group, a nitrile group, an aziridine group, an oxazoline group, a silanol group, and a hydrolyzable silyl group such as an alkoxysilane group. The reactive group-containing monomer may contain one or more polymerizable functional groups per molecule, or may be a macromonomer. The reactive group-containing monomer may be used alone or in combination of two or more.

[0034] As the reactive group-containing monomer, for example, at least one selected from the group consisting of an epoxy group-containing monomer and a hydrolyzable silyl group-containing monomer is preferably used. More specifically, for example, (i) an embodiment in which the reactive group-containing monomer includes an epoxy group-containing monomer and a monomer containing a functional group capable of reacting with an epoxy group, and (ii) an embodiment in which the reactive group-containing monomer includes a hydrolyzable silyl group-containing monomer can be mentioned.

[0035] Examples of epoxy group-containing monomers include glycidyl (meth)acrylate, 3,4-epoxybutyl (meth)acrylate, 3,4-epoxycyclohexyl (meth)acrylate, vinyl glycidyl ether, allyl glycidyl ether, 2-methylallyl glycidyl ether, 3,4-epoxy-1-butene, 3,4-epoxy-1-methyl-1-butene, 3,4-epoxy-1-pentene, 3,4-epoxy-3-methyl-1-pentene, 5,6-epoxy-1-hexene, 1,2-vinylcyclohexene monoepoxide, and styrene-p-glycidyl ether. Examples of functional groups reactive with epoxy groups include carboxy groups, acid anhydride groups, sulfonic acid groups, amino groups, hydroxyl groups, and isocyanate groups. From the viewpoint of reactivity with epoxy groups, the amino group-containing monomer is preferably a primary or secondary amine, and more preferably a secondary amine. These functional groups can react with epoxy groups to form crosslinks.

[0036] After hydrolysis, the hydrolyzable silyl groups can form crosslinks by condensation with each other through thermal dehydration.The hydrolyzable silyl groups are not particularly limited, but examples thereof include alkoxysilyl groups, acyloxysilyl groups, alkenyloxysilyl groups, aryloxysilyl groups, halogenated silyl groups, and silyl groups having an amide group, an amino group, an aminooxy group, or a ketoximate group.From the viewpoint of reactivity, the hydrolyzable silyl group is preferably an alkoxysilyl group, and more preferably a methoxysilyl group or an ethoxysilyl group.The hydrolyzable silyl group-containing monomer can be, for example, a silane coupling agent having a structure containing the above-mentioned butadiene-derived structural unit.

[0037] When the polymerizable monomer includes the reactive group-containing monomer, the content of the reactive group-containing monomer relative to 100 parts by mass of the polymerizable monomer is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more, while from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less.

[0038] In the powder of the present disclosure, the styrene-acrylic resin used as the binder resin may be a polymer of a polymerizable monomer containing styrene, a (meth)acrylic acid ester, and a crosslinkable macromonomer. The crosslinkable macromonomer is as described above. The polymer of the polymerizable monomer forms crosslinks within the polymer by reaction of polymerizable functional groups contained in the crosslinkable macromonomer, or the polymerizable functional groups remain unreacted and can be crosslinked by heat or electron beams. By using the powder of the present disclosure containing such a polymer as a binder resin, the polymers contained in the electromagnetic wave absorbing layer can be crosslinked, thereby improving the strength of the electromagnetic wave absorbing layer.

[0039] When the polymerizable monomer includes the above-mentioned crosslinkable macromonomer, the content of the crosslinkable macromonomer relative to 100 parts by mass of the polymerizable monomer is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more, while from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less.

[0040] In the present disclosure, the acrylic resin is a polymer of polymerizable monomers that includes a (meth)acrylic monomer and does not include an aromatic vinyl monomer, and may further be copolymerized with other monomers different from the (meth)acrylic monomer or the aromatic vinyl monomer, as long as the object of the present disclosure is not impaired. Note that the (meth)acrylic monomer used in the acrylic resin is preferably the above-mentioned monovinyl monomer, but may also be a macromonomer or a crosslinkable polymerizable monomer.

[0041] The polymerizable monomer used in the acrylic resin preferably contains a (meth)acrylic monomer as the monovinyl monomer, and more preferably contains at least one selected from the group consisting of acrylic acid esters and methacrylic acid esters as the monovinyl monomer. In order to achieve excellent dispersibility of Additive A when melting the powder of the present disclosure and to improve the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, the acrylic acid ester used in the acrylic resin may be an alkyl acrylate ester having an alkyl group containing 1 to 12 carbon atoms, an alkyl acrylate ester having an alkyl group containing 1 to 10 carbon atoms, or an alkyl acrylate ester having an alkyl group containing 1 to 8 carbon atoms, and among these, at least one selected from the group consisting of butyl acrylate, propyl acrylate, and 2-ethylhexyl acrylate is preferred. From the same viewpoint as above, the methacrylic acid ester used in the acrylic resin may be an alkyl methacrylate ester having an alkyl group having 1 to 12 carbon atoms, an alkyl methacrylate ester having an alkyl group having 1 to 10 carbon atoms, or an alkyl methacrylate ester having an alkyl group having 1 to 8 carbon atoms, and among these, at least one selected from the group consisting of methyl methacrylate, butyl methacrylate, propyl methacrylate, and 2-ethylhexyl methacrylate is preferred.

[0042] The content of (meth)acrylic monomer units in the acrylic resin is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. Here, the (meth)acrylic monomer units may be monomer units derived from a monovinyl monomer, a crosslinkable polymerizable monomer, or a macromonomer.

[0043] The structure and proportion of each monomer unit constituting the polymer contained in the base particle can be determined from the composition of the polymerizable monomer used when producing the base particle. １ It can be determined from the integral value obtained by H-NMR measurement.

[0044] In the present disclosure, the content of either the styrene-acrylic resin or the acrylic resin is preferably 90% by mass or more, more preferably 95% by mass or more, even more preferably 99% by mass or more, and particularly preferably 100% by mass, relative to 100% by mass of the total amount of binder resins. This can improve the dispersibility of Additive A when melting the powder of the present disclosure.

[0045] As the binder resin, a polyester resin is also preferably used. In view of the fact that the powder of the present disclosure has the desired electrostatic charge property, that the dispersibility of additive A is excellent when the powder of the present disclosure is melted, and that the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure is improved, at least one selected from the group consisting of a styrene-acrylic resin, an acrylic resin, and a polyester resin is preferably used as the binder resin, at least one selected from the group consisting of a styrene-acrylic resin and an acrylic resin is more preferably used, and a styrene-acrylic resin is particularly preferably used.

[0046] The polyester resin may be, for example, a polyester resin obtained by polycondensation of a carboxylic acid component containing a polycarboxylic acid compound and an alcohol component containing a polyhydric alcohol. The carboxylic acid component is a compound containing a carboxyl group or a carboxylic acid derivative group, and the polycarboxylic acid compound is a compound having two or more carboxyl groups or carboxylic acid derivative groups per molecule. Examples of the carboxylic acid derivative group include an amide group, an ester group, an acid anhydride group, and an acid halide. The carboxylic acid component and the alcohol component may each be used alone or in combination of two or more.

[0047] Polylactic acid (PLA) can also be used as the polyester resin, which is preferably used because it is biodegradable and therefore reduces the burden on the environment.

[0048] As the binder resin, known thermoplastic resins such as organic polymer materials, such as epoxy resin, polyvinyl chloride, ethylene-vinyl acetate copolymer, fluorine-containing polymer, polyamide, polyester, silicone resin, polyurethane resin, polycarbonate resin, synthetic rubber, and foamed polystyrene, can also be used.

[0049] In the present disclosure, the binder resin may further contain a styrene-acrylic resin and a thermoplastic resin different from the styrene-acrylic resin. This improves the strength of the electromagnetic wave absorbing layer and enables the electromagnetic wave absorbing layer to be made thinner. Examples of binder resins containing a styrene-acrylic resin and a thermoplastic resin different from the styrene-acrylic resin include a binder resin containing a styrene-acrylic resin, which is a polymer of a polymerizable monomer containing styrene and a (meth)acrylic acid ester, and at least one resin selected from the group consisting of a polycarbonate resin and a polyester resin. When the binder resin further contains a thermoplastic resin different from the styrene-acrylic resin, the content thereof is not particularly limited, but from the viewpoint of compatibility, it may be, for example, 0.5 to 10% by mass, or 1 to 5% by mass, relative to 100% by mass of the total amount of the binder resin.

[0050] In the present disclosure, the binder resin may contain a resin that can be crosslinked by heat or electron beams. This improves the strength of the electromagnetic wave absorbing layer formed by melt-molding the powder of the present disclosure, since the binder resins are crosslinked with each other during melt-molding. Examples of resins that can be crosslinked by heat or electron beams include polymers of polymerizable monomers containing styrene, a (meth)acrylic acid ester, and the reactive group-containing monomer described above. Examples of resins that can be crosslinked by heat or electron beams include polymers of polymerizable monomers containing styrene, a (meth)acrylic acid ester, and the crosslinkable macromonomer described above.

[0051] The binder resin used in the present disclosure preferably has a glass transition temperature (Tg) of 20 to 110°C, more preferably 30 to 100°C, and even more preferably 50 to 90°C. When the Tg of the binder resin is within the above range, the powder of the present disclosure has good fluidity and storage stability at room temperature, and it becomes easy to form a uniform layer using the powder of the present disclosure. In the present disclosure, the glass transition temperature (Tg) can be determined, for example, in accordance with ASTM D3418-82. Specifically, a sample is heated at a heating rate of 10°C / min using a differential scanning calorimeter (such as SSC5200 manufactured by Seiko Instruments Inc.), and the temperature showing the maximum endothermic peak in the DSC curve obtained during this process can be taken as the glass transition temperature.

[0052] The content of the binder resin contained in the base particles is not particularly limited, but from the viewpoint of improving the thermal fixability of the powder of the present disclosure, it is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 96 parts by mass or more, relative to 100 parts by mass of the base particles, and from the viewpoint of sufficiently containing a charge control agent, etc., it is preferably 99 parts by mass or less, more preferably 98 parts by mass or less.

[0053] <Crosslinkable Resin> The base particles may further contain at least one crosslinkable resin selected from the group consisting of thermosetting resins and electron beam curable resins. By containing a crosslinkable resin, an electromagnetic wave absorbing layer having excellent strength can be formed using the powder of the present disclosure. The crosslinkable resin can be appropriately selected from known thermosetting resins and electron beam curable resins and is not particularly limited, but for example, at least one selected from the group consisting of epoxy resins and maleimide resins can be preferably used.

[0054] Examples of the epoxy resin include bixylenol type epoxy resin, bisphenol A type epoxy resin, bisphenol F type epoxy resin, bisphenol S type epoxy resin, bisphenol AF type epoxy resin, dicyclopentadiene type epoxy resin, trisphenol type epoxy resin, naphthol novolac type epoxy resin, phenol novolac type epoxy resin, tert-butyl-catechol type epoxy resin, naphthalene type epoxy resin, naphthol type epoxy resin, anthracene type epoxy resin, glycidylamine type epoxy resin, and glycidyl ester type epoxy resin. , cresol novolac type epoxy resins, phenol aralkyl type epoxy resins, biphenyl type epoxy resins, linear aliphatic epoxy resins, epoxy resins having a butadiene structure, alicyclic epoxy resins, heterocyclic epoxy resins, spiro ring-containing epoxy resins, cyclohexane type epoxy resins, cyclohexane dimethanol type epoxy resins, naphthylene ether type epoxy resins, trimethylol type epoxy resins, tetraphenylethane type epoxy resins, isocyanurate type epoxy resins, phenolphthalimidine type epoxy resins, phenolphthalein type epoxy resins, and the like.

[0055] Examples of the maleimide resin include bismaleimide resins such as 4,4'-diphenylmethane bismaleimide, m-phenylene bismaleimide, bisphenol A diphenyl ether bismaleimide, 3,3'-dimethyl-5,5'-diethyl-4,4'-diphenylmethane bismaleimide, 4-methyl-1,3-phenylene bismaleimide, and 1,6'-bismaleimide-(2,2,4-trimethyl)hexane, and polymers having a maleimide group such as "MIR-3000-70MT" or "MIR-5000-60T" manufactured by Nippon Kayaku Co., Ltd.

[0056] The number average molecular weight of the crosslinkable resin is not particularly limited, but may be, for example, 1,000 to 100,000, since crosslinking is easily formed and the strength of the electromagnetic wave absorbing layer is easily improved.

[0057] When the powder of the present disclosure contains the crosslinkable resin, the content of the crosslinkable resin relative to 100 parts by mass of the binder resin is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more, while from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less.

[0058] <Silane Coupling Agent> The base particles may further contain a silane coupling agent. By including a silane coupling agent, when the powder of the present disclosure is melt-molded, crosslinks are formed through a hydrolysis reaction of the hydrolyzable silyl groups of the silane coupling agent and a subsequent condensation reaction due to thermal dehydration. Therefore, the powder of the present disclosure can be used to form an electromagnetic wave absorbing layer with excellent strength. Since a silane coupling agent containing a polymerizable functional group corresponds to the above-mentioned hydrolyzable silyl group-containing monomer, a silane coupling agent used separately from the binder resin may be a silane coupling agent that does not contain a polymerizable functional group. The silane coupling agent may be a known silane coupling agent, and is not particularly limited. For example, a silane coupling agent containing a hydrolyzable silyl group and at least one reactive group selected from the group consisting of a hydroxyl group, an amino group, an epoxy group, a thiol group, an isocyanate group, a carboxyl group, an acid anhydride group, a sulfonic acid group, a chlorosulfonic acid group, a phosphate group, a nitrile group, an aziridine group, and an oxazoline group is preferably used because it easily improves the strength of the electromagnetic wave absorbing layer.

[0059] When the powder of the present disclosure contains the silane coupling agent, the content of the silane coupling agent relative to 100 parts by mass of binder resin is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more, while from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less.

[0060] <Charge Control Agent> As the charge control agent, a positively or negatively charged charge control agent is used. From the viewpoint of imparting the desired charge property to the particles while improving the dispersibility of additive A when the powder of the present disclosure is melted, a polar compound having charge property is preferably used as the charge control agent. Furthermore, a negatively charged charge control agent is preferably used from the viewpoint of being highly effective in improving the dispersibility of additive A and further improving the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed from the powder of the present disclosure.

[0061] The charge control agent is preferably a polymeric compound, and a charge control resin is particularly preferred, in order to improve the dispersibility of Additive A when the powder of the present disclosure is melted. Examples of charge control resins that can be used include copolymers containing functional group-containing monomer units (sometimes simply referred to as "functional group-containing copolymers" in this disclosure). Examples of positively charged charge control resins include functional group-containing copolymers containing structural units containing functional groups such as pyridinium groups, amino groups, quaternary ammonium groups, or quaternary ammonium salt-containing groups, such as polyamine resins, quaternary ammonium group-containing copolymers, and quaternary ammonium base-containing copolymers. Examples of negatively charged charge control resins include functional group-containing copolymers containing structural units containing functional groups such as sulfonic acid groups, sulfonate salt-containing groups, carboxyl groups, or carboxylate salt-containing groups, such as sulfonic acid group-containing copolymers, sulfonate salt group-containing copolymers, carboxyl group-containing copolymers, and carboxylate salt group-containing copolymers. The functional group-containing copolymer may be, for example, a copolymer obtained by copolymerizing a monomer containing a functional group with another monomer copolymerizable therewith, or may be a copolymer obtained by polymerizing a monomer not containing a functional group and then introducing a functional group by a modification treatment.

[0062] The functional group-containing copolymer preferably has a content of functional group-containing monomer units (sometimes simply referred to as "functional group amount" in the present disclosure) of 0.4 to 10% by mass, since this allows the particles to be imparted with the desired electrostatic charge. The lower limit of the functional group amount of the functional group copolymer is more preferably 1% by mass or more, and even more preferably 2% by mass or more, and the upper limit is more preferably 9% by mass or less, and even more preferably 8% by mass or less.

[0063] From the viewpoint of compatibility with the binder resin, the functional group-containing copolymer is preferably a styrene-acrylic resin, and more preferably a copolymer containing a functional group-containing monomer unit, an aromatic vinyl monomer unit, and a (meth)acrylic monomer unit. Here, the aromatic vinyl monomer unit and the (meth)acrylic monomer unit do not contain a functional group that imparts chargeability. Such a copolymer has excellent compatibility with the binder resin, and therefore tends to produce particles with a uniform charge amount.

[0064] In the functional group-containing copolymer, the copolymerization ratio of the aromatic vinyl monomer units and the (meth)acrylic monomer units is not particularly limited, but from the viewpoint of compatibility with the binder resin, the mass ratio of the (meth)acrylic monomer units to the aromatic vinyl monomer units ((meth)acrylic monomer units / aromatic vinyl monomer units) is preferably 0.05 to 0.35, more preferably 0.10 to 0.30, and even more preferably 0.15 to 0.25.

[0065] The glass transition temperature (Tg) of the charge control resin is not particularly limited, but is preferably in the range of 50° C. to 110° C., and more preferably in the range of 55° C. to 100° C. When the glass transition temperature (Tg) of the charge control resin is in the above range, aggregation of particles can be suppressed.

[0066] The weight-average molecular weight (Mw) of the charge control resin is not particularly limited, but is preferably in the range of 4,000 to 35,000, and more preferably in the range of 5,000 to 30,000. When the weight-average molecular weight (Mw) is equal to or greater than the lower limit, particle aggregation can be suppressed, and when it is equal to or less than the upper limit, a decrease in the thermal fixability of the powder of the present disclosure can be suppressed. Furthermore, when the weight-average molecular weight (Mw) of the charge control resin is within the above range, the charge control resin can be suitably dispersed in the base particles, making it easier to obtain a powder imparted with a stable charge amount over time. In the present disclosure, the weight-average molecular weight (Mw) is a polystyrene-equivalent value measured by gel permeation chromatography (GPC) using tetrahydrofuran (THF).

[0067] The base particles may contain a relatively low molecular weight charge control compound as a charge control agent. Examples of positively chargeable charge control compounds include nigrosine dyes, quaternary ammonium salts, triaminotriphenylmethane compounds, and imidazole compounds. Examples of negatively chargeable charge control compounds include azo dyes containing metals such as Cr, Co, Al, and Fe, salicylic acid metal compounds, and alkylsalicylic acid metal compounds.

[0068] The content of the charge control agent is not particularly limited, but the lower limit is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the binder resin, from the viewpoint of imparting the desired chargeability and improving the dispersibility of Additive A when melting the powder of the present disclosure, thereby improving the electromagnetic wave absorption characteristics of the formed electromagnetic wave absorbing layer. The upper limit is preferably 5 parts by mass or less, more preferably 3 parts by mass or less, from the viewpoint of suppressing a decrease in charge stability. Furthermore, a content of the charge control agent within the above range is also preferable because it is easy to control the number ratio of particles containing Additive A within the desired range. Furthermore, from the same viewpoints as above, the content of the charge control agent is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the polymerizable monomer, and is preferably 5 parts by mass or less, more preferably 3 parts by mass or less. Furthermore, from the viewpoint of imparting the desired chargeability and improving the dispersibility of Additive A when the powder of the present disclosure is melted, thereby improving the electromagnetic wave absorption characteristics of the electromagnetic wave absorbing layer to be formed, the content of the charge control resin in 100% by mass of the charge control agent is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. The charge control agents can be used singly or in combination of two or more.

[0069] <Additive A> In the present disclosure, additive A is at least one additive selected from the group consisting of carbon nanotubes, carbon nanohorns, and carbon fibers. Additive A is a fibrous carbon compound capable of reflecting electromagnetic waves. These additives A can be used alone or in combination of two or more.

[0070] As additive A, carbon nanotubes are preferably used because they have excellent dispersibility when the powder of the present disclosure is melted and because an electromagnetic wave absorbing layer with excellent electromagnetic wave absorption properties is easily formed. Known carbon nanotubes can be used without any particular limitation. They may be single-walled carbon nanotubes (SWCNTs) or multi-walled carbon nanotubes (MWCNTs), or branched carbon nanotubes. Among these, single-walled carbon nanotubes (SWCNTs) are preferably used because they have excellent dispersibility when the powder of the present disclosure is melted, thereby enabling the formation of an electromagnetic wave absorbing layer with particularly excellent electromagnetic wave absorption properties. Single-walled carbon nanotubes (SGCNTs) obtained by the super growth method may also be used as single-walled carbon nanotubes. The carbon purity of the carbon nanotubes is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 98% by mass. The higher the carbon purity of the carbon nanotubes, the better the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed from the powder of the present disclosure. Impurities other than carbon contained in carbon nanotubes include, for example, metal compounds derived from the catalyst used during production, catalyst carriers such as silica, etc. Furthermore, from the viewpoint of improving the dispersibility of carbon nanotubes when melting the powder of the present disclosure and improving the electromagnetic wave absorption characteristics of the formed electromagnetic wave absorbing layer, the average diameter of the carbon nanotubes is preferably 1 to 15 nm, more preferably 1 to 10 nm. From the same viewpoint as above, the BET specific surface area of ​​the carbon nanotubes is preferably 500 to 2000 m ２ / g, and 700 to 1700m ２ / g, and more preferably 800 to 1500m ２ / g. Furthermore, it is preferable that the t-plot obtained from the adsorption isotherm of the carbon nanotubes exhibits an upwardly convex shape. The "t-plot" can be obtained by converting the relative pressure of the carbon nanotubes measured by the nitrogen gas adsorption method into the average thickness t (nm) of the nitrogen gas adsorption layer. That is, the average thickness t of the nitrogen gas adsorption layer corresponding to the relative pressure is calculated from a known standard isotherm in which the average thickness t of the nitrogen gas adsorption layer is plotted against the relative pressure P / P0, and the conversion is then performed to obtain the t-plot of the carbon nanotubes (the t-plot method by de Boer et al.).

[0071] The carbon nanohorn may be any known material and is not particularly limited. The carbon fiber may be any known material and is not particularly limited, but examples thereof include polyacrylonitrile carbon fiber and coiled carbon fiber. The average diameter of the carbon fiber is preferably 1 μm or more, more preferably 1 to 10 μm, and even more preferably 3 to 7 μm.

[0072] The powder of the present disclosure can exhibit excellent electromagnetic wave absorption properties even when the content of additive A is small. Therefore, excellent electromagnetic wave absorption properties are exhibited even when the content of additive A per 100 parts by mass of binder resin is about 0.01 parts by mass. The content of additive A per 100 parts by mass of binder resin is not particularly limited, but from the viewpoint of improving the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, it is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more. The upper limit is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 0.5 parts by mass or less, and even more preferably 0.2 parts by mass or less, from the viewpoint of suppressing deterioration of the dispersibility of additive A when melting the powder of the present disclosure and suppressing deterioration of the electromagnetic wave absorption properties of the formed electromagnetic wave absorbing layer. For the same reasons as above, the content of additive A relative to 100 parts by mass of polymerizable monomer is preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, even more preferably 0.1 parts by mass or more, and is preferably 2.0 parts by mass or less, more preferably 1.5 parts by mass or less, even more preferably 0.5 parts by mass or less, and still more preferably 0.2 parts by mass or less. The content of additive A is the total content of carbon nanotubes, carbon nanohorns, and carbon fibers.

[0073] In the powder of the present disclosure, 5 to 95% by number of particles out of 100% by number of particles contain the additive A dispersed in a binder resin, and the remaining particles do not contain additive A. Note that "not containing additive A" means that none of carbon nanotubes, carbon nanohorns, or carbon fibers are contained. For example, even when the powder of the present disclosure contains only carbon nanotubes as additive A, "not containing additive A" means that none of carbon nanotubes, carbon nanohorns, or carbon fibers are contained. From the viewpoint of suppressing variation in the performance of the electromagnetic wave absorbing layer formed from the powder of the present disclosure and improving the electromagnetic wave absorption characteristics, it is preferable that the powder of the present disclosure does not contain particles to which the additive A has been externally added. In other words, it is preferable that none of carbon nanotubes, carbon nanohorns, or carbon fibers is externally added to the particles constituting the powder of the present disclosure. When the number ratio of particles containing the additive A dispersed in the binder resin is within the above range, the electromagnetic wave absorbing layer formed from the powder of the present disclosure can exhibit excellent electromagnetic wave absorption properties and also exhibit excellent uniformity in performance of the electromagnetic wave absorbing layer. From this perspective, the number ratio of particles containing the additive A dispersed in the binder resin is preferably 10 to 80% by number, more preferably 20 to 60% by number. The number ratio of particles containing the additive A dispersed in the binder resin can be determined, for example, by determining the average Munsell value of each particle cross-section from a TEM image of the cross-section of the particles constituting the powder, determining the presence or absence of additive A from the average Munsell value, and calculating the ratio of the number of particles containing additive A to the total number of measured particles. Furthermore, in a TEM image of the cross-section of a particle, if the additive A is only attached to the outer edge of the particle, it is determined that the additive A is added externally, and if the additive A is embedded in the particle, it is determined that the additive A is dispersed in the binder resin.

[0074] <Additive B> In the present disclosure, additive B is at least one additive selected from the group consisting of amorphous carbon, graphite, graphene, fullerene, metal oxide magnetic material, and metal magnetic material. Additive B is an additive having electromagnetic wave absorbing properties, and is a carbon compound (other than additive A) or a magnetic material used to impart electromagnetic wave absorbing properties to conventional electromagnetic wave absorbers. These additives B can be used alone or in combination of two or more.

[0075] Examples of amorphous carbon include carbon black, such as acetylene black, ketjen black, channel black, furnace black, lamp black, and thermal black.

[0076] Examples of the metal oxide magnetic material include Fe ２ O ３ MnO, ZnO, NiO, MgO, CuO or Li ２ Ferrite with a combination of O, etc.: NiO-MnO-ZnO-Fe ２ O ３ , MnO-ZnO-Fe ２ O ３ (Mn-Zn ferrite), NiO-ZnO-Fe ２ O ３ Spinel ferrites such as (Ni-Zn ferrites); garnet ferrites; spinel (cubic) γ-Fe ２ O ３ , γ-Fe ４ O ４ Examples of the metallic magnetic material include pure iron-based metal powder, iron nitride powder, Fe—Si—Al alloy (Sendust), Ni—Fe alloy (Permalloy), Co—Fe alloy, and amorphous alloy having an Fe base or a Co base.

[0077] The powder of the present disclosure can exhibit excellent electromagnetic wave absorption properties by containing particles containing the additive A at a specific number ratio. Therefore, even if the content of the additive B is significantly reduced compared to conventional electromagnetic wave absorbers, or even if the additive B is not contained at all, the powder of the present disclosure exhibits excellent electromagnetic wave absorption properties. Furthermore, by setting the content of the additive B to a specific amount or less, the electromagnetic wave absorption properties of the powder of the present disclosure can be further improved. From this perspective, the content of the additive B is preferably 20 parts by mass or less, more preferably less than 12 parts by mass, even more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the binder resin. On the other hand, the powder of the present disclosure may contain the additive B within a range that does not impair the object of the present disclosure. When the powder of the present disclosure contains the additive B, it is preferable that at least a portion of the particles constituting the powder of the present disclosure contain the additive B in a dispersed state in the binder resin. When the powder of the present disclosure contains the additive B, the content thereof may be, for example, 0.01 parts by mass or more or 0.05 parts by mass or more relative to 100 parts by mass of the binder resin. The content of additive B refers to the total content of amorphous carbon, graphite, graphene, fullerene, metal oxide magnetic material, and metal magnetic material.

[0078] <Other Additives> In the present disclosure, the base particles may contain a styrene-based thermoplastic elastomer. Here, the term "styrene-based thermoplastic elastomer" refers to a random, block, or graft copolymer of a styrene-based monomer with at least one other monomer, such as a monoolefin or diolefin copolymerizable with the styrene-based monomer, as well as a hydrogenated product of such a copolymer. A typical example of a thermoplastic elastomer is one that can be deformed to 200% by volume at room temperature (20°C) with a small external force, assuming its original volume to be 100% by volume, and that returns to less than 130% by volume when the external force is removed. A typical example of a styrene-based thermoplastic elastomer is a block copolymer containing at least one aromatic vinyl polymer block and at least one conjugated diene polymer block. Specific preferred examples of the styrene-based thermoplastic elastomer include styrene-isoprene-styrene block copolymer (SIS), styrene-butadiene-styrene block copolymer (SBS), styrene-ethylene / propylene-styrene block copolymer (SEPS), styrene-ethylene / butylene-styrene block copolymer (SEBS), etc. The styrene-based thermoplastic elastomers that can be used in the present disclosure are not limited to the representative examples and specific examples described above.

[0079] <Shell Layer> The base particles may be so-called core-shell type (also called "capsule type") particles having a core layer containing the binder resin and a shell layer covering the core layer. In the core-shell type base particles, the softening point of the shell layer is preferably higher than that of the core layer. This allows for a good balance between the thermal fixability and storage stability of the powder.

[0080] The shell layer may contain, for example, a polymer of a polymerizable monomer for the shell. The polymerizable monomer for the shell can be the same as the polymerizable monomer described above that is the raw material for the binder resin contained in the core layer. Among these, it is preferable to use, as the polymerizable monomer for the shell, polymerizable monomers that can give a polymer with a Tg of more than 80°C, such as styrene, acrylonitrile, and methyl methacrylate, either alone or in combination.

[0081] The content of the shell layer is not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the binder resin. The content of the shell layer is also not particularly limited, but is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, relative to 100 parts by mass of the polymerizable monomer. The content of the polymer of the shell polymerizable monomer contained in 100% by mass of the shell layer is preferably 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more. It is particularly preferred that the shell layer be made of a polymer of the shell polymerizable monomer.

[0082] 1-2. External Additives The particles constituting the powder of the present disclosure may be composed of the above-mentioned mother particles, but from the viewpoint of improving the fluidity of the powder of the present disclosure and improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, it is preferable that the powder further contains an external additive. Examples of external additives include inorganic fine particles such as silica, titanium oxide, aluminum oxide, zinc oxide, tin oxide, calcium carbonate, calcium phosphate, cerium oxide, barium titanate, and strontium titanate; fine particles of fatty acid metal salts such as zinc stearate and magnesium stearate; and organic fine particles such as polymethyl methacrylate resin, silicone resin, and melamine resin. Among these, inorganic fine particles are preferred, and among inorganic fine particles, at least one type of fine particles selected from the group consisting of silica fine particles and titanium oxide fine particles are preferred, with silica fine particles being particularly preferred.

[0083] The external additive may be hydrophobized, and among these, hydrophobized silica fine particles are preferably used. Examples of the hydrophobizing agent include a silane coupling agent, a silicone oil, a fatty acid, and a fatty acid metal salt.

[0084] The above-mentioned external additives can be used alone, but it is preferable to use two or more of them in combination. In particular, it is preferable to use two or more types of silica fine particles with different particle sizes in combination. When two or more types of silica fine particles with different particle sizes are used in combination as external additives, in order to improve the fluidity of the powder of the present disclosure and improve the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure, it is preferable to contain at least two types of silica fine particles with a difference in number-average primary particle size of 5 to 50 nm, and it is more preferable to contain at least two types of silica fine particles with a difference in number-average primary particle size of 10 to 40 nm. The number-average primary particle size of the external additive is measured, for example, by weighing out about 0.1 g of a measurement sample, placing it in a beaker, adding 0.1 mL of an alkylbenzenesulfonic acid aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) as a dispersant, further adding 10 to 30 mL of a diluent (manufactured by Beckman Coulter, product name: Isoton II) to the beaker, and dispersing the mixture for 3 minutes using a 20 W (Watt) ultrasonic disperser. Thereafter, the number-average primary particle size is measured using a particle size distribution analyzer (manufactured by Beckman Coulter, product name: Multisizer) under the conditions of an aperture diameter of 100 μm, a medium: Isoton II, and a measurement particle count of 100,000.

[0085] Furthermore, from the viewpoint of facilitating electrostatic adhesion of the powder of the present disclosure, when the base particles contain a positively charged charge control agent, it is preferable that they contain a positively charged external additive, and when the base particles contain a negatively charged charge control agent, it is preferable that they contain a negatively charged external additive.

[0086] The content of the external additive is not particularly limited, but the lower limit is preferably 0.01 parts by mass or more, more preferably 0.1 parts by mass or more, and even more preferably 1.0 parts by mass or more, relative to 100 parts by mass of the base particles. The upper limit is preferably 20 parts by mass or less, more preferably 10 parts by mass or less, and even more preferably 5 parts by mass or less. When the content of the external additive is equal to or greater than the above-mentioned lower limit, the effect of improving the fluidity of the powder of the present disclosure and the effect of improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure are further enhanced. When the content of the external additive is equal to or less than the above-mentioned upper limit, the surface smoothness of the electromagnetic wave absorbing layer formed from the powder of the present disclosure is improved. Furthermore, it is preferable that the content of the external additive is within the above-mentioned range from the viewpoint of thinning the electromagnetic wave absorbing layer formed from the powder of the present disclosure.

[0087] 1-3. Powder Characteristics The particles constituting the powder of the present disclosure have a volume average particle size (Dv) of 2 to 100 μm. This allows the particles to be uniformly arranged. The lower limit of the volume average particle size of the particles constituting the powder of the present disclosure is preferably 3 μm or more, more preferably 5 μm or more, from the viewpoint of improving the flowability of the powder of the present disclosure and improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure. The upper limit is preferably 80 μm or less, more preferably 50 μm or less, and even more preferably 20 μm or less, from the viewpoint of reducing the thickness of the electromagnetic wave absorbing layer.

[0088] The particles constituting the powder of the present disclosure preferably have a ratio (Dv / Dp) of volume average particle diameter (Dv) to number average particle diameter (Dp) of 1.0 or more and less than 1.3, more preferably 1.0 or more and 1.2 or less. When Dv / Dp is less than 1.3, the flowability of the powder of the present disclosure is likely to be good, and the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure can be improved. The volume average particle diameter and number average particle diameter of the particles can be measured, for example, using a particle size distribution measuring device using the Coulter Counter method (for example, a Multisizer product name manufactured by Beckman Coulter).

[0089] The average circularity of the particles constituting the powder of the present disclosure is preferably 0.94 or more, more preferably 0.95 or more, and even more preferably 0.96 or more, from the viewpoint of improving the fluidity of the powder of the present disclosure and improving the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure. The average circularity of the particles constituting the powder of the present disclosure is 1 or less, and when the measurement sample is a perfect sphere, the average circularity is 1. In the present disclosure, circularity is the value obtained by dividing the perimeter of a circle having the same projected area as the particle image by the perimeter of the projected image of the particle. The average circularity is an index indicating the degree of unevenness of the surface of the measurement sample and can be used as a simple method for quantitatively expressing the shape of particles. The more complex the surface shape of the measurement sample, the smaller the average circularity. The circularity of particles can be determined, for example, by using an aqueous solution in which particles are dispersed as a sample liquid, taking a projected image of the particles in the sample liquid using a flow particle image analyzer (for example, FPIA-2100, manufactured by CIMEX Corporation), measuring the perimeter of a circle equal to the projected area of ​​the particle and the perimeter of the projected image of the particle from the projected image, and then using the following calculation formula 1. The average circularity is the average value of the circularities of the particles contained in the sample liquid. Calculation formula 1: (Circularity) = (Perimeter of a circle equal to the projected area of ​​the particle) / (Perimeter of the projected image of the particle)

[0090] The absolute value of the charge per unit area of ​​the powder of the present disclosure is 40 to 1500 mC / cm ２ This allows the powder of the present disclosure to be electrostatically attached to a support. Furthermore, when the absolute value of the charge amount per unit area of ​​the powder of the present disclosure is equal to or greater than the above lower limit, the particles are more easily arranged uniformly when the powder of the present disclosure is electrostatically attached to the surface of a support, and when it is equal to or less than the above upper limit, the powder of the present disclosure can be electrostatically attached even more easily to the surface of a support. Furthermore, when the absolute value of the charge amount per unit area of ​​the powder of the present disclosure is within the above range, this is also preferred from the viewpoint of thinning the electromagnetic wave absorbing layer formed from the powder of the present disclosure. From this viewpoint, the absolute value of the charge amount per unit area of ​​the powder of the present disclosure is 50 to 1000 mC / cm ２ In the present disclosure, the charge amount per unit area of ​​the powder (unit: mC / cm ２) is the powder's blow-off charge (unit: μC / g) relative to the powder's BET specific surface area (unit: cm ２ / kg). The blow-off charge (unit: μC / g) of a powder is measured using a blow-off charge measurement device based on the blow-off method. The specific measurement method is as follows: 9.95 g of carrier and 0.05 g of sample (powder) are weighed out, placed in a 100 cc glass bottle, and rotated at 150 rpm for 30 minutes. After that, nitrogen gas is blown at a pressure of 4.5 kPa and sucked at a pressure of 9.5 kPa, and the charge of the mixture of carrier and sample (measurement sample mixture) is measured under an environment of a temperature of 23°C and a relative humidity of 50%. The blow-off charge (unit: μC / g) of the sample can be calculated using the following formula from the measured charge of the measurement sample mixture, the mass of the measurement sample mixture, and the content of the sample in the measurement sample mixture. Blow-off charge (μC / g) = charge of measurement sample mixture (μC) / (mass of measurement sample mixture (g) × content ratio of sample in measurement sample mixture) The BET specific surface area of ​​the powder is measured by nitrogen adsorption method (BET method). The charge per unit area of ​​the powder of the present disclosure can be adjusted within the above-mentioned specific range, for example, by using a binder resin with chargeability, or by disposing an external additive with chargeability on the particle surface when using a binder resin without chargeability. Furthermore, the absolute value of the charge per unit area of ​​the powder of the present disclosure can be adjusted by adjusting the volume average particle size of the particles or the type and content of the external additive.

[0091] The surface resistivity of the surface layer of the powder of the present disclosure is not particularly limited, but is preferably 8.0 to 12.0 Log Ω / □, and more preferably 9.0 to 11.0 Log Ω / □, which provides a good balance between chargeability and transferability. １０ The surface layer of the powder is the surface of a molded body obtained by compressing the powder without melting it. The surface resistivity of the surface layer can be adjusted to fall within the above range by adjusting the type and content of the external additive.

[0092] The angle of repose of the powder of the present disclosure is preferably 15 to 45°, more preferably 20 to 40°, even more preferably 20 to 35°, and even more preferably 20 to 33°. The angle of repose of a powder can be used as an indicator of the fluidity of the powder, and the lower the angle of repose, the higher the fluidity tends to be. When the angle of repose of the powder of the present disclosure is equal to or greater than the above-mentioned lower limit, the performance uniformity of the electromagnetic wave absorbing layer formed from the powder of the present disclosure can be improved, and when it is equal to or less than the above-mentioned upper limit, particle aggregation can be suppressed, thereby improving the performance uniformity of the electromagnetic wave absorbing layer. The angle of repose of the powder of the present disclosure can be kept within the above-mentioned range by adjusting the volume average particle size of the particles and the type and content of external additives.

[0093] The melting temperature of the powder of the present disclosure has a lower limit of preferably 70°C or higher, more preferably 80°C or higher, and an upper limit of preferably 140°C or lower, more preferably 120°C or lower. When the melting temperature of the powder of the present disclosure is equal to or higher than the lower limit, particle aggregation can be suppressed. When the melting temperature of the powder of the present disclosure is equal to or lower than the upper limit, the performance uniformity of the formed electromagnetic wave absorbing layer can be improved. In addition, it is preferable that the melting temperature of the powder of the present disclosure is within the above range in terms of excellent storage stability of the powder of the present disclosure. The melting temperature of the powder of the present disclosure is the temperature at which the powder of the present disclosure starts to melt.

[0094] The melting temperature (T1 / 2) of the powder of the present disclosure in the 1 / 2 method is preferably 110°C or higher, more preferably 120°C or higher, even more preferably 130°C or higher, and even more preferably 150°C or higher as a lower limit, and is preferably 260°C or lower, more preferably 250°C or lower, and even more preferably 240°C or lower, and may be 190°C or lower, or may be 180°C or lower. The melting temperature (T1 / 2) in the 1 / 2 method can be determined from the melt viscosity measured under the following measurement conditions using a flow tester (manufactured by Shimadzu Corporation, trade name: CFT-500C). <Measurement conditions> Measurement starting temperature: 40°C, heating rate: 3°C / min, preheating time: 5 minutes, cylinder pressure: 10 kgf / cm ２, die diameter: 0.5 mm, die length: 1.0 mm. The melting temperature (T1 / 2) can be used as an indicator of the fixing temperature of the powder. When the melting temperature (T1 / 2) of the powder of the present disclosure is equal to or higher than the lower limit, thermal melting of the particles is suppressed, thereby suppressing particle aggregation. When the melting temperature (T1 / 2) of the powder of the present disclosure is equal to or lower than the upper limit, unevenness in the formed electromagnetic wave absorbing layer is suppressed, thereby improving the performance uniformity of the formed electromagnetic wave absorbing layer. In addition, it is preferable that the melting temperature (T1 / 2) of the powder of the present disclosure is within the above range in terms of excellent storage stability of the powder of the present disclosure and the ability to form a uniform, thin electromagnetic wave absorbing layer. The melting temperature (T1 / 2) in the 1 / 2 method is not simply the softening temperature, but the temperature at which half of the sample comes out of the nozzle when a sample is placed in a cylinder, heated, and a weight is placed on it. This serves as an indicator of the fixing temperature physical properties when thermally fixing the powder, rather than the melting initiation temperature. Measurement of the melting temperature (T1 / 2) by the 1 / 2 method can be a simple test of the viscoelasticity of a powder.

[0095] The glass transition temperature (Tg) of the powder of the present disclosure is not particularly limited, but is preferably 20 to 110° C., more preferably 30 to 100° C., and even more preferably 50 to 90° C. When the Tg is within the above range, the powder of the present disclosure has good fluidity and storage stability at room temperature, and also makes it easy to form a uniform layer using the powder of the present disclosure.

[0096] 2. Powder Manufacturing Method The powder manufacturing method of the present disclosure includes at least the step of manufacturing the above-described base particles, and may further include the step of attaching an external additive to the surface of the base particles. The method of manufacturing the base particles used in the present disclosure and the method of attaching an external additive to the surface of the base particles, i.e., the external addition treatment, will be described in detail below.

[0097] 2-1. Method for Producing Base Particles The method for producing the base particles is not particularly limited, but a production method using a suspension polymerization method is preferred because it is easy to control the number ratio of particles containing the additive A. When producing base particles using a suspension polymerization method, the number ratio of particles containing the additive A can be controlled by adjusting the type or content of the polymerizable monomer used, or the type or content of the charge control agent, etc. In order to keep the number ratio of particles containing the additive A within the above-mentioned preferred range, for example, it is preferable to use a polymer of polymerizable monomers in which the total content of an aromatic vinyl monomer and a (meth)acrylic acid alkyl ester having an alkyl group having 6 or less carbon atoms and having no acidic functional group, hydroxyl group, or amino group is 90% by mass or more as the binder resin. Here, examples of aromatic vinyl monomers that are preferably used include styrene, vinyl toluene, and α-methylstyrene, with styrene being particularly preferred. Examples of (meth)acrylic acid alkyl esters having an alkyl group containing 6 or less carbon atoms and not containing an acidic functional group, a hydroxyl group, or an amino group include, for example, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, butyl (meth)acrylate, pentyl (meth)acrylate, and hexyl (meth)acrylate. Among these, methyl (meth)acrylate, ethyl (meth)acrylate, propyl (meth)acrylate, and butyl (meth)acrylate are particularly preferred. Furthermore, the lower the content of the charge control agent, the lower the percentage of particles containing additive A. By adjusting the content of the charge control agent according to the binder resin composition and the type of charge control agent, the percentage of particles containing additive A can be adjusted to fall within the above range. As shown in Comparative Example 5 described below, when base particles are produced using a pulverization method, the percentage of particles containing additive A cannot be controlled, and all particles contain additive A.

[0098] The base particles used in the present disclosure can be produced, for example, by a suspension polymerization method, including the following steps: (1) preparing a polymerizable monomer composition containing at least a polymerizable monomer, a charge control agent, and an additive A (polymerizable monomer composition preparation step), (2) preparing a suspension in which droplets of the polymerizable monomer composition are dispersed in an aqueous medium containing a dispersion stabilizer (suspension step), and (3) subjecting the suspension to a polymerization reaction (polymerization step). Note that, in the production method described in the present disclosure, two or more of the steps may be performed simultaneously as a single step, or the order of the steps may be reversed, as far as technically possible.

[0099] (1) Preparation of Polymerizable Monomer Composition First, the polymerizable monomer, charge control agent, and additive A described above are mixed, and further, if necessary, a crosslinkable resin, a silane coupling agent, a molecular weight modifier, and the above-mentioned additive B and other additives to prepare a polymerizable monomer composition. For mixing when preparing the polymerizable monomer composition, a disperser such as an in-line type emulsifying disperser or a media type emulsifying disperser is used.

[0100] In the polymerizable monomer composition, the content of the polymerizable monomer is not particularly limited, but from the viewpoint of improving the thermal fixability of the powder of the present disclosure, it is preferably 90 parts by mass or more, more preferably 95 parts by mass or more, and even more preferably 96 parts by mass or more, relative to 100 parts by mass of the total solid content contained in the polymerizable monomer composition, and from the viewpoint of sufficiently containing a charge control agent, etc., it is preferably 99 parts by mass or less, more preferably 98 parts by mass or less. In the present disclosure, the solid content refers to all components other than the solvent, and liquid monomers, etc. are also included in the solid content.

[0101] In the polymerizable monomer composition, the content of the charge control agent is preferably 0.05 parts by mass or more, more preferably 0.1 parts by mass or more, relative to 100 parts by mass of the monovinyl monomer, as a lower limit, and preferably 5 parts by mass or less, more preferably 3 parts by mass or less. When the content of the charge control agent is equal to or greater than the lower limit, the desired chargeability can be imparted, and the dispersibility of Additive A can be improved when the powder of the present disclosure is melted, thereby improving the electromagnetic wave absorption characteristics of the electromagnetic wave absorbing layer formed from the powder of the present disclosure. When the content of the charge control agent is equal to or less than the upper limit, the charge stability of the powder of the present disclosure can be suppressed from decreasing. Furthermore, when the content of the charge control agent is within the above range, it is also preferable because it is easy to control the number ratio of particles containing Additive A within the desired range.

[0102] In the polymerizable monomer composition, the content of the additive A is, relative to 100 parts by mass of the monovinyl monomer, preferably 0.01 parts by mass or more, more preferably 0.05 parts by mass or more, and even more preferably 0.1 parts by mass or more as the lower limit, and preferably 2.0 parts by mass or less, more preferably 0.5 parts by mass or less, and even more preferably 0.2 parts by mass or less as the upper limit. When the content of the additive A is equal to or greater than the lower limit, the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed from the powder of the present disclosure can be improved, and when it is equal to or less than the upper limit, deterioration of the dispersibility of the additive A when the powder of the present disclosure is melted can be suppressed, and deterioration of the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed can be suppressed.

[0103] In the polymerizable monomer composition, the content of the additive B is preferably 20 parts by mass or less, more preferably less than 12 parts by mass, even more preferably 5 parts by mass or less, and even more preferably 1 part by mass or less, relative to 100 parts by mass of the monovinyl monomer. The content of the additive B may be, for example, 0.01 parts by mass or more, or 0.05 parts by mass or more, relative to 100 parts by mass of the monovinyl monomer. When the content of the additive B is equal to or less than the upper limit, deterioration of the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed from the powder of the present disclosure can be suppressed.

[0104] In the polymerizable monomer composition, the content of the crosslinkable resin is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more relative to 100 parts by mass of the polymerizable monomer. On the other hand, from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less. In the polymerizable monomer composition, the content of the silane coupling agent is not particularly limited, but from the viewpoint of improving the strength of the electromagnetic wave absorbing layer, it may be, for example, 0.5 parts by mass or more, 1.0 parts by mass or more, or 1.5 parts by mass or more relative to 100 parts by mass of the polymerizable monomer. On the other hand, from the viewpoint of improving the dispersibility of additive A when the powder of the present disclosure is melted, it may be, for example, 10.0 parts by mass or less, 7.0 parts by mass or less, or 5.0 parts by mass or less.

[0105] The molecular weight modifier is not particularly limited, and examples thereof include mercaptans such as t-dodecyl mercaptan, n-dodecyl mercaptan, n-octyl mercaptan, and 2,2,4,6,6-pentamethylheptane-4-thiol; thiuram disulfides such as tetramethylthiuram disulfide, tetraethylthiuram disulfide, tetrabutylthiuram disulfide, N,N'-dimethyl-N,N'-diphenylthiuram disulfide, and N,N'-dioctadecyl-N,N'-diisopropylthiuram disulfide; etc. These molecular weight modifiers can be used alone or in combination of two or more.

[0106] When the polymerizable monomer composition contains a molecular weight modifier, the content of the molecular weight modifier is appropriately adjusted so that the binder resin has a desired molecular weight, and is not particularly limited, but is usually 0.01 parts by mass or more and 10 parts by mass or less, and may be 0.1 parts by mass or more and 5 parts by mass or less, relative to 100 parts by mass of the monovinyl monomer.

[0107] The polymerizable monomer composition may further contain a polymerization initiator, which may be added in the suspension step described below. In particular, from the viewpoint of facilitating control of the molecular weight of the polymer, it is preferable to add the polymerization initiator in the suspension step described below after the polymerizable monomer composition is dispersed in an aqueous medium and before droplet formation.

[0108] (2) Suspension Step (Droplet Formation Step) Next, a suspension is prepared in which droplets of the polymerizable monomer composition obtained above are dispersed in an aqueous medium containing a dispersion stabilizer. The method for forming droplets of the polymerizable monomer composition is not particularly limited, but an example thereof is a method in which a mixed liquid obtained by mixing the polymerizable monomer composition with an aqueous medium containing a dispersion stabilizer is vigorously stirred. Examples of devices capable of vigorously stirring the mixture include an (in-line type) emulsifying disperser (manufactured by Pacific Machinery Works, Ltd., product name: Milder) and a high-speed emulsifying disperser (manufactured by Primix Corporation, product name: T.K. Homomixer MARK II Type).

[0109] In the present disclosure, an aqueous medium refers to a medium containing water as a main component. It is preferable that the aqueous medium contain a dispersion stabilizer. Examples of dispersion stabilizers include inorganic compounds such as sulfates (e.g., barium sulfate, calcium sulfate, etc.); carbonates (e.g., barium carbonate, calcium carbonate, magnesium carbonate, etc.); phosphates (e.g., calcium phosphate); metal oxides (e.g., aluminum oxide, titanium oxide, etc.); metal hydroxides (e.g., aluminum hydroxide, magnesium hydroxide, ferric hydroxide, etc.); and organic compounds such as water-soluble polymers (e.g., polyvinyl alcohol, methyl cellulose, gelatin, etc.); anionic surfactants; nonionic surfactants; and amphoteric surfactants. These dispersion stabilizers can be used alone or in combination of two or more. Among the above dispersion stabilizers, inorganic compounds are preferred, and colloids of poorly water-soluble inorganic compounds are more preferred, with colloids of poorly water-soluble metal hydroxides being particularly preferred. By using a colloid of an inorganic compound, preferably a colloid of a poorly water-soluble inorganic compound, particularly preferably a colloid of a poorly water-soluble metal hydroxide, the particle size distribution of the base particles can be narrowed and the amount of dispersion stabilizer remaining after washing can be reduced, thereby improving the electromagnetic wave absorption properties of the electromagnetic wave absorbing layer formed using the obtained powder.

[0110] A poorly water-soluble metal hydroxide colloid can be prepared, for example, by reacting at least one selected from the group consisting of alkali metal hydroxides and alkaline earth metal hydroxides with a water-soluble polyvalent metal salt (excluding alkaline earth metal hydroxides) in an aqueous medium. Examples of alkali metal hydroxides include lithium hydroxide, sodium hydroxide, and potassium hydroxide. Examples of alkaline earth metal hydroxides include barium hydroxide and calcium hydroxide. Examples of water-soluble polyvalent metal salts include water-soluble polyvalent metal salts other than the above-mentioned alkaline earth metal hydroxides. Examples of water-soluble polyvalent metal salts include magnesium metal salts such as magnesium chloride, magnesium phosphate, and magnesium sulfate; calcium metal salts such as calcium chloride, calcium nitrate, calcium acetate, and calcium sulfate; aluminum metal salts such as aluminum chloride and aluminum sulfate; barium salts such as barium chloride, barium nitrate, and barium acetate; and zinc salts such as zinc chloride, zinc nitrate, and zinc acetate. Among these, magnesium metal salts, calcium metal salts, and aluminum metal salts are preferred, magnesium metal salts are more preferred, and magnesium chloride is particularly preferred. The method for reacting at least one selected from the group consisting of the alkali metal hydroxides and alkaline earth metal hydroxides with the water-soluble polyvalent metal salt in an aqueous medium is not particularly limited, and examples thereof include a method of mixing an aqueous solution of at least one selected from the group consisting of the alkali metal hydroxides and alkaline earth metal hydroxides with an aqueous solution of the water-soluble polyvalent metal salt. Furthermore, colloidal silica can also be used as the colloid of a poorly water-soluble inorganic compound, i.e., a colloidal dispersion containing colloidal particles of a poorly water-soluble inorganic compound.

[0111] The content of the dispersion stabilizer is appropriately adjusted so as to obtain particles of the desired particle size. It is not particularly limited, but is preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8.0 parts by mass, relative to 100 parts by mass of the polymerizable monomer in the polymerizable monomer composition. The content of the dispersion stabilizer is preferably 0.5 to 10 parts by mass, more preferably 1.0 to 8.0 parts by mass, relative to 100 parts by mass of the monovinyl monomer. The content of the dispersion stabilizer is typically 1 to 15 parts by mass, preferably 1 to 8 parts by mass, relative to 100 parts by mass of the aqueous medium. By ensuring that the content of the dispersion stabilizer is equal to or greater than the lower limit, droplets of the polymerizable monomer composition can be sufficiently dispersed so as not to coalesce in the suspension. On the other hand, by ensuring that the content of the dispersion stabilizer is equal to or less than the upper limit, an increase in the viscosity of the suspension during granulation can be prevented, thereby avoiding the problem of the suspension clogging in the granulator.

[0112] In the present disclosure, when preparing the suspension, it is preferable to further add a polymerization initiator to a mixed liquid of the polymerizable monomer composition and an aqueous medium containing a dispersion stabilizer. Examples of the polymerization initiator include persulfates such as potassium persulfate and ammonium persulfate; azo compounds such as 4,4'-azobis(4-cyanovaleric acid), 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide), 2,2'-azobis(2-amidinopropane) dihydrochloride, 2,2'-azobis(2,4-dimethylvaleronitrile), and 2,2'-azobisisobutyronitrile; and organic peroxides such as di-t-butyl peroxide, benzoyl peroxide, t-butylperoxy-2-ethylhexanoate, t-butylperoxydiethylacetate, t-hexylperoxy-2-ethylbutanoate, diisopropyl peroxydicarbonate, di-t-butylperoxyisophthalate, and t-butylperoxyisobutyrate. These polymerization initiators can be used alone or in combination of two or more. Among these, organic peroxides are preferred because they can reduce the amount of residual polymerizable monomer. Among organic peroxides, peroxyesters are preferred because they have good initiator efficiency and can reduce the amount of residual polymerizable monomer, and non-aromatic peroxyesters, i.e., peroxyesters without an aromatic ring, are more preferred. As described above, the polymerization initiator may be added after the polymerizable monomer composition is dispersed in an aqueous medium and before droplet formation, or it may be added to the polymerizable monomer composition before it is dispersed in an aqueous medium.

[0113] The amount of the polymerization initiator used in the polymerization of the polymerizable monomer composition is not particularly limited, but is preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the polymerizable monomer. The amount of the polymerization initiator added is also preferably 0.1 to 20 parts by mass, more preferably 0.3 to 15 parts by mass, and even more preferably 1 to 10 parts by mass, relative to 100 parts by mass of the monovinyl monomer.

[0114] (3) Polymerization Step: By subjecting the suspension obtained above to a polymerization reaction, the polymerizable monomer is polymerized to form a binder resin, resulting in a dispersion in an aqueous medium in which particles containing the binder resin and the charge control agent dispersed in the binder resin are dispersed. The particles obtained by subjecting the suspension to a polymerization reaction may be used as base particles as they are, or the particles obtained by subjecting the suspension to a polymerization reaction may form a core layer, and the surface of the core layer may be coated with a shell layer to form base particles. The polymerization reaction of the polymerizable monomer contained in the suspension can be carried out, for example, by heating the suspension. The polymerization temperature is preferably 50°C or higher, more preferably 60 to 95°C. The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours.

[0115] The method for producing core-shell type base particles having a core layer obtained by subjecting a suspension to a polymerization reaction and a shell layer covering the core layer is not particularly limited, and the base particles can be produced by a conventionally known method. In terms of production efficiency, an in situ polymerization method or a phase separation method is preferred.

[0116] A method for producing core-shell base particles by in situ polymerization is described below. The suspension is subjected to a polymerization reaction, and the resulting particles are dispersed in an aqueous dispersion medium. The above-described polymerizable monomer for the shell and a polymerization initiator are added to the aqueous dispersion medium, and the resulting particles are polymerized to obtain core-shell base particles. The content of the polymerizable monomer for the shell is preferably 0.1 to 10 parts by mass, more preferably 0.5 to 7 parts by mass, and even more preferably 1 to 5 parts by mass, per 100 parts by mass of the monovinyl monomer.

[0117] Examples of the polymerization initiator used in the polymerization of the shell polymerizable monomer include water-soluble polymerization initiators such as metal persulfates, such as potassium persulfate and ammonium persulfate; and azo initiators, such as 2,2'-azobis(2-methyl-N-(2-hydroxyethyl)propionamide) and 2,2'-azobis(2-methyl-N-(1,1-bis(hydroxymethyl)2-hydroxyethyl)propionamide). These polymerization initiators can be used alone or in combination of two or more. The amount of the polymerization initiator is preferably 0.1 to 30 parts by mass, more preferably 1 to 20 parts by mass, per 100 parts by mass of the shell polymerizable monomer.

[0118] The polymerization temperature for the shell layer is preferably 50° C. or higher, more preferably 60 to 95° C. The polymerization reaction time is preferably 1 to 20 hours, more preferably 2 to 15 hours.

[0119] (4) Washing, Filtration, Dehydration, and Drying Steps After the polymerization is completed, the aqueous dispersion of base particles obtained by polymerization is preferably subjected to washing, filtration, dehydration, and drying steps for removing the dispersion stabilizer according to a conventional method, which are repeated several times as necessary.

[0120] As for the above-mentioned washing method, when an inorganic compound is used as the dispersion stabilizer, it is preferable to add an acid or alkali to the aqueous dispersion of the base particles to dissolve and remove the dispersion stabilizer in water. When a colloid of a poorly water-soluble metal hydroxide is used as the dispersion stabilizer, it is preferable to add an acid to adjust the pH of the aqueous dispersion of the base particles to 6.5 or less. The acid to be added may be an inorganic acid such as sulfuric acid, hydrochloric acid, or nitric acid, or an organic acid such as formic acid or acetic acid, but sulfuric acid is particularly preferred because of its high removal efficiency and its small burden on the production equipment.

[0121] The dehydration and filtration methods can be any known method, and are not particularly limited. Examples include centrifugal filtration, vacuum filtration, pressure filtration, etc. The drying method is also not particularly limited, and various methods can be used.

[0122] 2-2. External Addition Treatment The external addition treatment for adhering an external additive to the surface of the base particles is not particularly limited, and can be carried out, for example, by mixing and stirring the base particles together with the external additive using a stirrer. The stirrer used for the external addition treatment is not particularly limited as long as it is a stirring device that can adhere an external additive to the surface of the base particles, and examples thereof include FM Mixer (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.), Super Mixer (trade name, manufactured by Kawada Manufacturing Co., Ltd.), Q Mixer (trade name, manufactured by Nippon Coke and Engineering Co., Ltd.), Mechanofusion System (trade name, manufactured by Hosokawa Micron Corporation), and Mechano Mill (trade name, manufactured by Okada Seiko Co., Ltd.).

[0123] 3. Electromagnetic Wave Absorber The electromagnetic wave absorber of the present disclosure is characterized by comprising the melt-molded product of the powder of the present disclosure described above as an electromagnetic wave absorbing layer. The electromagnetic wave absorber of the present disclosure may also be composed of the melt-molded product of the powder of the present disclosure described above. The melt-molded product of the powder of the present disclosure has electromagnetic wave absorbing properties over a wider frequency range than conventional products, such as 30 to 100 GHz, and therefore can be used as an electromagnetic wave absorbing layer or electromagnetic wave absorber. Furthermore, the electromagnetic wave absorber of the present disclosure can exhibit stable electromagnetic wave absorbing properties because the performance variation of the melt-molded product of the powder of the present disclosure, which serves as the electromagnetic wave absorbing layer, is suppressed.

[0124] Examples of the electromagnetic wave absorber of the present disclosure include an electromagnetic wave absorber comprising a support and an electromagnetic wave absorbing layer disposed on at least a portion of the surface of the support, wherein the electromagnetic wave absorbing layer is a melt-molded product of the powder of the present disclosure, and the melt-molded product of the powder of the present disclosure itself.

[0125] The shape of the electromagnetic wave absorbing layer, which is a melt-molded product of the powder of the present disclosure, is not particularly limited and may be any desired shape depending on the application. Meanwhile, by using the powder of the present disclosure, it is possible to form a thin electromagnetic wave absorbing layer. From the viewpoint of thinning, the thickness of the electromagnetic wave absorbing layer is preferably 5 mm or less, more preferably 2 mm or less, and even more preferably 0.8 mm or less. Meanwhile, from the viewpoint of fully exhibiting the electromagnetic wave absorbing properties, the thickness is preferably 0.05 mm or more, more preferably 0.1 mm or more. Furthermore, from the viewpoint of fully exhibiting the electromagnetic wave absorbing properties, the width of the electromagnetic wave absorbing layer, which is a melt-molded product of the powder of the present disclosure, is preferably 1 cm or more.

[0126] The support provided in the electromagnetic wave absorber of the present disclosure is not particularly limited, but it preferably has a smooth surface so that the powder of the present disclosure can be easily electrostatically attached and thermally fixed. The shape of the support is not particularly limited. The powder of the present disclosure can be attached to the surface of a support having any shape.

[0127] The electromagnetic wave absorber of the present disclosure may include an electromagnetic wave reflecting layer. In this case, it is preferable that the electromagnetic wave absorbing layer, which is a melt-molded product of the powder of the present disclosure, is disposed on the surface side of the electromagnetic wave reflecting layer. The electromagnetic wave reflecting layer can also be used as a support. Examples of the electromagnetic wave reflecting layer include films vapor-deposited with metals such as silver, gold, aluminum, copper, tin, nickel, and ITO. The film is not particularly limited, and examples include films made of non-conductive materials such as plastic materials and paper. The vapor-deposited metal layer allows the film to exhibit electromagnetic wave reflection properties. The thickness of the vapor-deposited metal layer is preferably 0.01 μm to 3 mm. If the thickness is less than 0.01 μm, the mechanical strength decreases, and if it exceeds 3 mm, the weight of the electromagnetic wave reflecting layer becomes too heavy to be practical. In this case, it is preferable to design the film taking into account the shielding ability for the target electromagnetic wave frequency band.

[0128] 4. Manufacturing Method of Electromagnetic Wave Absorber The manufacturing method of the electromagnetic wave absorber of the present disclosure is not particularly limited. Because the electromagnetic wave absorber of the present disclosure comprises a melt-molded product of the powder of the present disclosure as an electromagnetic wave absorbing layer, the manufacturing method thereof typically includes melting the powder of the present disclosure and cooling the melted powder. When the electromagnetic wave absorber of the present disclosure is itself a melt-molded product of the powder of the present disclosure, the electromagnetic wave absorber of the present disclosure can be manufactured by melt-molding the powder of the present disclosure into a desired shape using a known method. The conditions for melt-molding the powder of the present disclosure are not particularly limited, but it is preferable to melt the powder at a temperature 5 to 90°C higher than the melting temperature of the powder, and more preferably to melt the powder at a temperature 10 to 80°C higher than the melting temperature of the powder.

[0129] When the powder of the present disclosure contains a binder resin crosslinkable by heat or an electron beam, a crosslinkable resin crosslinkable by heat or an electron beam, or both, the method for producing an electromagnetic wave absorber of the present disclosure may be a method comprising melting the powder of the present disclosure, thermally crosslinking the crosslinkable binder resin or crosslinkable resin contained in the molten powder, and then cooling the molten powder. Alternatively, the method may be a method comprising melting the powder of the present disclosure, cooling the molten powder to obtain a molded body, and then crosslinking the crosslinkable binder resin or crosslinkable resin contained in the molded body with an electron beam. Furthermore, when the powder of the present disclosure contains a silane coupling agent, the method for producing an electromagnetic wave absorber of the present disclosure may be a method comprising melting the powder of the present disclosure, thermally crosslinking the silane coupling agent contained in the molten powder, and then cooling the molten powder. Note that "crosslinking a silane coupling agent by heat" refers to crosslinking by hydrolyzing the hydrolyzable silyl groups of the silane coupling agent, followed by condensation by thermal dehydration. By crosslinking the binder resin, crosslinkable resin, or silane coupling agent in this manner, a melt-molded product with excellent strength can be obtained. The method for thermally crosslinking the crosslinkable binder resin, crosslinkable resin, or silane coupling agent contained in the molten powder of the present disclosure is not particularly limited, and can be carried out, for example, by melting the powder at the above-mentioned melting temperature to obtain a melt, and then maintaining the temperature of the melt at the melting temperature for 10 minutes to 1 hour. The method for crosslinking the crosslinkable binder resin or crosslinkable resin contained in the molten powder of the present disclosure with an electron beam is not particularly limited, and can be carried out, for example, by melting the powder, cooling it to obtain a molded product, and then irradiating the molded product with an electron beam.

[0130] The powder of the present disclosure, which has high fluidity, can be electrostatically charged and electrically transferred to a support, and then thermally fixed to the support, using a method similar to that used for developers in electrophotography, etc. In this case, the powder of the present disclosure melts and solidifies when thermally fixed to the support, and becomes a molten molded product after fixing. As a method for thermally fixing the powder of the present disclosure, a method of thermally melting and fixing using, for example, a heat roller or belt is preferred, as this is advantageous for achieving a high-speed, uniform, and fine electromagnetic wave absorbing pattern.

[0131] An example of a method for producing an electromagnetic wave absorber according to the present disclosure includes the following steps: (1) preparing a support; (2) charging the powder according to the present disclosure; (3) electrostatically attaching the charged powder to at least a portion of the surface of the support; and (4) melt-bonding the powder to the support to form an electromagnetic wave absorbing layer that is a melt-molded body of the powder. According to this method, an electromagnetic wave absorber can be obtained that includes a support and an electromagnetic wave absorbing layer formed on at least a portion of the surface of the support.

[0132] In the above-described manufacturing method, when the powder of the present disclosure contains a crosslinkable binder resin or a crosslinkable resin, the crosslinkable binder resin or crosslinkable resin contained in the molten powder may be crosslinked by heat when the powder is melt-bonded to the support in the above-described step (4), or the crosslinkable binder resin or crosslinkable resin contained in the molded body obtained after the powder is melt-bonded to the support may be crosslinked by an electron beam. Also, when the powder of the present disclosure contains a silane coupling agent, the silane coupling agent contained in the molten powder may be crosslinked by heat when the powder is melt-bonded to the support in the above-described step (4).

[0133] Examples of methods for charging the powder of the present disclosure include a method of stirring the powder of the present disclosure together with a carrier, a method of charging by friction between the powder and a blade, a method of charging the powder on a charging roll, etc. Examples of carriers include magnetic powders such as iron powder, ferrite powder, and nickel powder, glass beads, and those whose surfaces have been treated with a fluorine-based resin, a styrene-acrylic resin, a silicone resin, or the like.

[0134] The charged powder of the present disclosure can adhere to at least a portion of the surface of a support by electrostatic force. As a method for melting and adhering the powder adhered to the support, for example, a method using a heated roller or belt, as described above, can be mentioned.

[0135] The applications of the powder and electromagnetic wave absorber of the present disclosure are not particularly limited, but include, for example, use to prevent malfunction of electronic devices or communication devices that use electromagnetic waves. More specific examples include electromagnetic wave absorbers used in automobile collision prevention systems or false start prevention systems, and electromagnetic wave absorbers used in expressway electronic toll collection systems (ETC). Furthermore, electromagnetic wave absorbers using the powder of the present disclosure can achieve electromagnetic wave absorption performance in the 30 to 100 GHz frequency band, making them suitable for use in various mobile electronic devices such as current mobile phones and wireless LANs. Because these applications require a fine pattern of the electromagnetic wave absorbing layer, the powder of the present disclosure, which allows for thin-film electromagnetic wave absorbing layers, is ideally used. Similar applications are expected to expand to higher GHz bands in the future.

[0136] The present disclosure will be described in more detail below with reference to examples and comparative examples, but the present disclosure is not limited to these examples. Note that parts and percentages are by mass unless otherwise specified. The weight-average molecular weight Mw of the resin was determined in polystyrene equivalent by GPC. The measurement sample was prepared by dissolving the polymer in tetrahydrofuran (THF) to a concentration of 2 mg / mL, sonicating for 10 minutes, and then passing the solution through a 0.45 μm membrane filter. The measurement conditions were: temperature: 40°C, solvent: tetrahydrofuran, flow rate: 1.0 mL / min, concentration: 0.2 wt%, sample injection volume: 100 μL, and a GPC TSKgel Multipore HXL-M (30 cm x 2 columns) manufactured by Tosoh Corporation.

[0137] [Production Example 1: Production of Silica Microparticles 1] 100 g of silica microparticles (trade name: Aerosil 50, manufactured by Nippon Aerosil Co., Ltd.) having a number-average primary particle diameter of 30 nm were dispersed in 600 g of toluene, and 7.3 g of 3-aminopropyltriethoxysilane was added and dispersed and mixed for 15 minutes to bring the mixture into contact with the silica. Next, 5.2 g of trifluoropropyltrimethoxysilane was added and dispersed and mixed for 15 minutes to bring the mixture into contact with the silica. The resulting dispersion was distilled under reduced pressure, dried, and crushed to obtain hydrophobic, positively charged silica microparticles 1. The obtained silica microparticles 1 had a number-average primary particle diameter of 50 nm and a charge per unit area of ​​+3,300 mC / cm. ２ It was.

[0138] [Production Example 2: Production of Silica Microparticles 2] Hydrophobic positively charged silica microparticles 2 were obtained in the same manner as in the above-mentioned Production Example 1, except that silica microparticles having a number-average primary particle diameter of 40 nm (product name: Aerosil 50OX, manufactured by Nippon Aerosil Co., Ltd.) were used instead of silica microparticles having a number-average primary particle diameter of 30 nm. The obtained silica microparticles 2 had a number-average primary particle diameter of 80 nm and a charge per unit area of ​​+3000 mC / cm. ２ It was.

[0139] Example 1 1. Production of Base Particles A mixture of 37.5 parts of styrene, 12.5 parts of n-butyl acrylate, 50 parts of methyl methacrylate, and 0.1 part of a polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., product name "AA-6", glass transition temperature 94°C) as polymerizable monomers, 1 part of a negatively charged charge control resin CCR1 (manufactured by Fujikura Chemical Industries, Ltd., product name "FCA626N", amount of sulfonic acid group-containing monomer 7%, weight average molecular weight 26,800, glass transition temperature 58°C) as a charge control agent, and super growth single-walled carbon nanotubes (manufactured by Zeon Corporation, product name "ZEONANO (registered trademark) SG101", average diameter: 3.5 nm, BET specific surface area: 1449 m) as additive A was used. ２ / g, t-plot is upwardly convex, carbon purity: 99.6%, mainly containing single-walled CNTs) was mixed and dispersed using an in-line emulsifying disperser (trade name: Milder, manufactured by Pacific Machinery Works, Ltd.) to prepare a polymerizable monomer composition.

[0140] Separately, at room temperature, an aqueous solution prepared by dissolving 15.2 parts of magnesium chloride (a water-soluble polyvalent metal salt) in 250 parts of ion-exchanged water was gradually added with stirring to an aqueous solution prepared by dissolving 8.1 parts of sodium hydroxide (an alkali metal hydroxide salt) in 50 parts of ion-exchanged water to prepare a magnesium hydroxide colloid (a poorly water-soluble metal hydroxide colloid) dispersion, which was used as an aqueous medium containing a dispersion stabilizer.

[0141] The polymerizable monomer composition obtained above was added to the magnesium hydroxide colloid and further stirred, and 4.4 parts of t-butylperoxy-2-ethylhexanoate was added thereto as a polymerization initiator. The dispersion liquid to which the polymerization initiator had been added was dispersed at a rotation speed of 15,000 rpm using an in-line emulsifying disperser (trade name: Milder, manufactured by Pacific Machinery Works, Ltd.) to form droplets of the polymerizable monomer composition, thereby preparing a suspension.

[0142] The resulting suspension was placed in a reactor equipped with a stirring blade, and the temperature was raised to 90°C to carry out a polymerization reaction. After the polymerization conversion reached nearly 100%, an aqueous dispersion of the shell polymerizable monomer was obtained by micro-dispersing 2 parts of methyl methacrylate and 130 parts of water using an ultrasonic emulsifier. This aqueous dispersion was then further added to the reactor, along with 0.1 parts of 2,2'-azobis[2-methyl-N-(2-hydroxyethyl)-propionamide] (manufactured by Wako Pure Chemical Industries, Ltd., trade name: VA-086, water-soluble initiator) as a shell polymerization initiator. The temperature was then maintained at 95°C for 4 hours to further continue polymerization, after which the reaction was terminated by water cooling, yielding an aqueous dispersion of core-shell base particles. The base particle concentration in the resulting aqueous medium dispersion was 20% by mass.

[0143] To the aqueous dispersion of the base particles obtained above, sulfuric acid was added dropwise while stirring at room temperature, and acid washing was performed until the pH reached 6.5 or less. Next, filtration and separation were performed, and 500 parts of ion-exchanged water was added to the obtained solid matter to re-slurry it, and water washing treatment (washing, filtration, dehydration) was repeated several times. Next, filtration and separation were performed, and the obtained solid matter was placed in a container of a dryer and dried at 45°C for 48 hours to obtain dried base particles.

[0144] 2. External Addition Treatment To 100 parts of the dried base particles, 1.0 part of hydrophobicized negatively charged silica (manufactured by Clariant) having a number average primary particle size of 40 nm and 0.6 part of hydrophobicized negatively charged silica (manufactured by Nippon Aerosil Co., Ltd.) having a number average primary particle size of 12 nm were added as external additives, and the mixture was mixed and stirred using a 10 L capacity laboratory-scale high-speed stirrer equipped with a cooling jacket (manufactured by Nippon Coke and Engineering Co., Ltd., product name: FM Mixer) at a stirring blade peripheral speed of 40 m / sec for an external addition treatment time of 300 seconds, thereby performing external addition treatment, to obtain a powder of Example 1.

[0145] 3. Production of Electromagnetic Wave Absorber A lower plate, an upper plate, a molding frame, a plastic bag filled with powder, a hot plate, and a contact thermometer were prepared. Using the hot plate, the lower and upper plates were heated to 50°C while measuring with the contact thermometer. A molding frame was placed on the lower plate placed on the hot plate, and a plastic bag filled with powder was placed inside the molding frame. The upper plate was placed on top of the plastic bag, and the plastic bag filled with powder was sandwiched between the lower and upper plates. The temperature of the powder was measured with a contact thermometer and heated to 150°C. The powder was pressurized from the upper plate side, and the temperature of the hot plate was adjusted while checking the molten state of the powder. The temperature at which the powder started to melt was defined as the melting temperature (melting start temperature) of the powder. The melting temperatures (melting start temperature) of the powders obtained in each Example or Comparative Example are shown in Tables 1 to 4. Once the powder started to melt, a pressure of 1 grf / cm was applied from the upper plate side. ２ The powder was pressed for 1 minute under a weight of 1000 kJ / cm, compacted into a flat plate, and allowed to cool naturally to room temperature to obtain a flat plate-shaped electromagnetic wave absorber.

[0146] [Examples 2 to 12 and Comparative Examples 1 to 4, 6] Powders and electromagnetic wave absorbers of Examples 2 to 12 and Comparative Examples 1 to 4, 6 were obtained in the same manner as in Example 1, except that at least one of the material added to the polymerizable monomer composition in "1. Production of base particles", the material used to prepare the aqueous medium containing the dispersion stabilizer, and the external additive added in "2. External addition treatment" was changed according to Table 1, Table 2, or Table 4.

[0147] [Examples 13 to 14] Powders and electromagnetic wave absorbers of Examples 13 to 14 were obtained in the same manner as in Example 1, except that in the above "1. Production of base particles", additive B was further added to the polymerizable monomer composition according to Table 3.

[0148] [Examples 15 to 17] In the above "1. Production of mother particles", the polymerizable monomer used was changed according to Table 3, or a silane coupling agent was further added to the polymerizable monomer composition according to Table 3, and further, in the above "3. Production of electromagnetic wave absorber", the temperature was raised to 150°C, and when the powder started to melt, 1 grf / cm was applied from the upper plate side. ２The powders and electromagnetic wave absorbers of Examples 15 to 17 were obtained in the same manner as in Example 1, except that instead of the series of operations of pressing the powder for 1 minute under a weight of 1000 kJ / cm2, the powder was heated to 150°C and held at 150°C for 30 minutes under pressure.

[0149] [Examples 18 to 19] Powders and electromagnetic wave absorbers of Examples 18 to 19 were obtained in the same manner as in Example 1, except that in the above "1. Production of base particles", a binder resin was further added to the polymerizable monomer composition according to Table 3. The amount of crosslinkable resin added shown in Table 3 is the amount converted into solid content.

[0150] [Example 20] In the above "1. Production of mother particles", the polymerizable monomer used was changed according to Table 3, and further, in the above "3. Production of electromagnetic wave absorber", the temperature was raised to 150°C, and when the powder started to melt, 1 grf / cm was applied from the upper plate side. ２ The powder and electromagnetic wave absorber of Example 20 were obtained in the same manner as in Example 1, except that after the operation of pressing the powder for 1 minute under a weight of 1000 kV, an electron beam irradiation treatment was further carried out for 3 minutes at a pressure voltage of 500 kV and an irradiation density of 20 kGy using an EPS-800 electron beam irradiation device (manufactured by Nissin High Voltage Corporation).

[0151] The details of the abbreviations shown in Tables 1 to 4 are as follows: ST: styrene BA: n-butyl acrylate MMA: methyl methacrylate AA-6: polymethacrylic acid ester macromonomer (manufactured by Toagosei Co., Ltd., trade name "AA-6", glass transition temperature 94°C) EBECRYL820: polyester acrylate oligomer (manufactured by Daicel Allnex Co., Ltd., trade name "EBECRYL 820", hexafunctional acrylate) GMA: glycidyl methacrylate AMPS: 2-acrylamido-2-methylpropanesulfonic acid Silane coupling agent 1: silane coupling agent having a butadiene skeleton, an acid anhydride structure, and a trimethoxysilyl group, manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-12-1287A" Silane coupling agent 2: blocked isocyanate silane coupling agent, manufactured by Shin-Etsu Chemical Co., Ltd., trade name "X-12-1195" Polycarbonate: Mitsubishi Gas Chemical Company, Inc., trade name "Iupizeta (registered trademark) FPC-F124" PLA: Polylactic acid resin, Toray Industries, Inc., trade name "Ecodear (registered trademark) V911X51" CCR1: Negatively charged charge control resin, Fujikura Chemical Industries, Ltd., trade name "FCA626N", sulfonic acid group-containing monomer amount 7%, weight average molecular weight 26,800, glass transition temperature 58°C CCR2: Positively charged charge control resin, Fujikura Chemical Industries, Ltd., trade name "FCA700P", quaternary ammonium salt-containing monomer amount 2%, styrene acrylic resin, weight average molecular weight 5000, glass transition temperature 55°C SWCNT: Super growth single-walled carbon nanotubes (Zeon Corporation, trade name "ZEONANO (registered trademark) SG101", average diameter 3.5 nm, BET specific surface area 1449 m ２ / g, t-plot is upward convex, carbon purity 99.6%, mainly contains single-walled CNT) MWCNT: multi-walled carbon nanotube (manufactured by CNano Technology Ltd., product name "FloTube 9110", BET specific surface area 190 m ２ / g, average diameter 10 to 15 nm, length less than 10 μm, carbon purity 99.8% or more CB: Carbon black, manufactured by Mitsubishi Chemical Corporation, trade name "#25BS" Mn-Zn ferrite: Mn-Zn ferrite powder obtained by pulverizing "FEROTOP BSF-547" manufactured by Toda Kogyo Co., Ltd., trade name, to an average particle diameter (D50) of 3.2 μm Ni-Zn ferrite: Ni-Zn ferrite powder obtained by pulverizing "FEROTOP BSN-714" manufactured by Toda Kogyo Co., Ltd., trade name, to an average particle diameter (D50) of 0.5 μm Negatively chargeable silica (particle size 40 nm): hydrophobized negatively chargeable silica having a number average primary particle diameter of 40 nm (manufactured by Clariant) Negatively charged silica (particle size 12 nm): hydrophobized negatively charged silica having a number average primary particle size of 12 nm (manufactured by Nippon Aerosil Co., Ltd.) Positively charged silica (particle size 50 nm): silica microparticles 1 obtained in Production Example 1 above Positively charged silica (particle size 80 nm): silica microparticles 2 obtained in Production Example 2 above Zinc stearate: Sakai Chemical Industry Co., Ltd., product name "SPZ-100F"

[0152] [Comparative Example 5] Base particles prepared by the same procedure as in Example 1 were kneaded in a twin-screw extrusion kneader, coarsely pulverized in a pulverizer (registered trademark: Valperizer) manufactured by Sokyou Micron Co., Ltd., and then finely pulverized in an airflow jet mill manufactured by Nippon Pneumatic Mfg. Co., Ltd. The finely pulverized material was then classified using a cyclone to separate particles having a particle size of 6 μm or less from particles having a particle size of 25 μm or more, thereby obtaining base particles of Comparative Example 5. The obtained base particles were subjected to the same external addition treatment as in Example 1, thereby obtaining a powder of Comparative Example 5. Furthermore, an electromagnetic wave absorber of Comparative Example 5 was obtained using the powder of Comparative Example 5 by the same procedure as in Example 1.

[0153] The powder obtained in each of the examples and comparative examples was a powder containing 99.9% by mass or more of base particles containing a binder resin, a charge control agent dispersed in the binder resin, and particles containing an external additive.

[0154] [Measurement] (1) Number Proportion of Particles Containing Additive A Powder (particles) was dispersed in an epoxy resin and cured. The resulting cured product was cooled to -80°C and then cut with multiple microtomes to prepare thin sections. The cross sections of the thin sections were observed using a TEM (transmission electron microscope). The particle concentration was adjusted so that 20 to 30 particle cross sections could be observed within a 56 x 70 μm area at a magnification of 1,000 to 3,000 times. In the TEM image, the contrast was adjusted using a Munsell value of 10 / for the background without particles. The Munsell value was evaluated using a color sample. 100 particles with a size of 20 to 80% of the volume average particle size were randomly selected from the TEM image, and the average Munsell value of the selected particles, excluding the outer periphery, was calculated. Particles with an average Munsell value of 8 to 10 / were considered to be particles not containing Additive A. The number percentage (number %) of particles not containing additive A was determined, and the number percentage (number %) of particles not containing additive A was subtracted from 100 to obtain the number percentage (number %) of particles containing additive A. Tables 1 to 4 show the percentage of particles containing additive A. Note that particles containing additive A are particles containing additive A in a dispersed state in a binder resin.

[0155] (2) Volume-average particle size (Dv) Approximately 0.1 g of powder was weighed and placed in a beaker, and 0.1 mL of a surfactant aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) was added as a dispersant. 10 to 30 mL of Isoton II was further added to the beaker, and the mixture was dispersed for 3 minutes using a 20 W (Watt) ultrasonic disperser. Then, the volume-average particle size (Dv) of the particles constituting the powder was measured using a particle size distribution analyzer (manufactured by Beckman Coulter, Inc., product name: Multisizer) under the following conditions: aperture diameter: 100 μm, medium: Isoton II, number of particles measured: 100,000.

[0156] (3) Average Circularity 10 ml of ion-exchanged water was placed in a container, and 0.2 g of a surfactant aqueous solution (manufactured by Fujifilm Corporation, product name: Drywell) was added as a dispersant. 0.2 g of powder was then added, and the mixture was dispersed for 3 minutes at 60 W using an ultrasonic disperser. The particle concentration at the time of measurement was adjusted to 3,000 to 10,000 particles / μL, and 1,000 to 10,000 particles with a circle-equivalent diameter of 0.4 μm or more were measured using a flow particle image analyzer (manufactured by Sysmex Corporation, product name: FPIA-2100). The average circularity was calculated from the measured values. The circularity was calculated using the following formula, and the average circularity was taken as the average value: (Circularity) = (Perimeter of a circle equal to the projected area of ​​the particle) / (Perimeter of the projected image of the particle).

[0157] (4) Charge Amount Per Unit Area (4-1) Measurement of Blow-Off Charge Amount 9.95 g of carrier and 0.05 g of powder were weighed out, placed in a 100 cc glass bottle, and rotated at 150 rpm for 30 minutes. After that, using a blow-off meter (manufactured by Toshiba Chemical Corporation, trade name "TB-203"), nitrogen gas was blown at a pressure of 4.5 kPa and sucked at a pressure of 9.5 kPa under an environment of a temperature of 23°C and a relative humidity of 50%, and the charge amount of the mixture of carrier and sample (powder) (measurement sample mixture) was measured. The blow-off charge amount of the powder was calculated from the measured charge amount of the measurement sample mixture, the mass of the measurement sample mixture, and the content ratio of the sample (powder) in the measurement sample mixture using the following calculation formula. Blow-off charge amount (μC / g)=charge amount of measurement sample mixture (μC) / (mass (g) of measurement sample mixture × content ratio of sample in measurement sample mixture) For the carrier, in the measurement of negatively charged powders, a product manufactured by Powder Tech Co., Ltd. under the trade name "EF-80BS" (Mn-Mg-Sr-Fe system, no resin coating) was used, and for the measurement of positively charged powders, a product manufactured by Powder Tech Co., Ltd. under the trade name "F96-80" (Mn-Mg-Sr-Fe system, with silicone resin coating) was used.

[0158] (4-2) Measurement of Specific Surface Area The BET specific surface area of ​​the powder was measured by the nitrogen adsorption method (BET method) using a fully automatic BET specific surface area measuring device (manufactured by Mountec Co., Ltd., trade name: Macsorb HM model-1208).

[0159] (4-3) Calculation of charge amount per unit area The blow-off charge amount (unit: μC / g) of the powder obtained above was multiplied by the BET specific surface area (unit: cm) of the powder measured above. ２ / kg), the charge per unit area of ​​the powder (unit: mC / cm ２ ) was calculated.

[0160] (5) Angle of Repose Using a powder measuring instrument (manufactured by Hosokawa Micron Corporation, trade name "Powder Tester PT-E"), a sample funnel was placed on the stand of the instrument, and a standard sieve with a mesh size of 250 μm was placed on top of it. After fixing, the instrument was vibrated, and the powder was dropped through the sample funnel onto a circular table with a diameter of 8 cm, forming a mound of powder. The angle between the ridge of the mound and the horizontal line was measured as the angle of repose with a laser beam. The amplitude of the vibration was adjusted to an extent that the mound of powder would not collapse, and the falling speed of the powder was also adjusted.

[0161] (6) Melting Temperature (T1 / 2) by 1 / 2 Method Using a flow tester (manufactured by Shimadzu Corporation, product name: CFT-500C), the melt viscosity was measured under the following measurement conditions, and the melting temperature (T1 / 2) by the 1 / 2 method was calculated from the obtained melt viscosity. <Measurement Conditions> Measurement starting temperature: 40°C, heating rate: 3°C / min, preheating time: 5 min, cylinder pressure: 10 kgf / cm ２ , die diameter: 0.5 mm, die length: 1.0 mm

[0162] (7) Surface Resistivity The surface resistivity of the surface of a molded product obtained by compacting the powder without melting it was measured in accordance with JIS K 6911. The measurement was carried out using an R8340A (ultra-high resistance / microcurrent meter) and an R12702A (resistivity chamber) manufactured by Advantest Corporation under conditions of 20°C, 60% RH, and a voltage of 100V.

[0163] (8) Glass Transition Temperature (Tg) The glass transition temperature (Tg) of the powder was determined in accordance with ASTM D3418-82 using a differential scanning calorimeter (SSC5200, manufactured by Seiko Instruments Inc.) Using 5 mg of powder as a sample, the sample was heated at a heating rate of 10°C / min, and the temperature showing the maximum endothermic peak in the DSC curve obtained during this process was taken as the glass transition temperature (Tg).

[0164] [Evaluation] (9) Uniformity The gloss of the surface of the electromagnetic wave absorber was measured using a glossmeter (Gardner, USA, Gloss Guard, incident angle 60 degrees), and the uniformity of performance was evaluated according to the following criteria. Note that the higher the gloss of the surface of the electromagnetic wave absorber, the more uniform the dispersion of additive A and the more uniform the performance, such as electromagnetic wave absorption characteristics. On the other hand, the more non-uniform the dispersion state of additive A and the more aggregated particles there are, the lower the gloss due to diffuse reflection. (Evaluation Criteria) A: Gloss is 50% or more B: Gloss is 40% or more but less than 50% C: Gloss is 30% or more but less than 40% D: Gloss is less than 30% Furthermore, the higher the gloss of the surface of the electromagnetic wave absorber, the higher the smoothness of the surface of the electromagnetic wave absorber. High surface smoothness of the electromagnetic wave absorber means that the powder has melted and solidified by heat, and therefore means that the powder is heat-fixable. If the powder is not sufficiently melted, the smoothness of the surface of the electromagnetic wave absorber will be reduced, resulting in a decrease in gloss. In each of the Examples and Comparative Examples, the powder was fully melted and then solidified during the production of the electromagnetic wave absorber, so there was no decrease in gloss due to the influence of surface smoothness.

[0165] (10) Electromagnetic Wave Absorption Properties Using the electromagnetic wave absorber as a measurement sample, the electromagnetic wave absorption rate (%) was measured in the frequency ranges of 26.5 to 40 GHz, 40 to 60 GHz, and 75 to 110 GHz using a millimeter-wave compatible high-frequency dielectric property measurement system. The electromagnetic wave absorption rate values ​​(unit: %) at frequencies of 30 GHz, 50 GHz, and 100 GHz are shown in Tables 1 to 4. In addition, the electromagnetic wave absorption properties of the electromagnetic wave absorber were evaluated according to the following evaluation criteria. The evaluation results are shown in Tables 1 to 4. (Evaluation criteria) A: The electromagnetic wave absorption rate at 30 GHz is 30% or more, the electromagnetic wave absorption rate at 50 GHz is 40% or more, and the electromagnetic wave absorption rate at 100 GHz is 50% or more. B: The electromagnetic wave absorption rate at 30 GHz is 15% or more and less than 30%, the electromagnetic wave absorption rate at 50 GHz is 20% or more and less than 40%, and the electromagnetic wave absorption rate at 100 GHz is 25% or more and less than 50%. C: The electromagnetic wave absorption rate at 30 GHz is 5% or more and less than 15%, the electromagnetic wave absorption rate at 50 GHz is 10% or more and less than 20%, and the electromagnetic wave absorption rate at 100 GHz is 10% or more and less than 25%. D: The electromagnetic wave absorption rate at 30 GHz is less than 5%, the electromagnetic wave absorption rate at 50 GHz is less than 10%, and the electromagnetic wave absorption rate at 100 GHz is less than 10%.

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[0169]

[0170] [Discussion] In Comparative Example 1, the volume average particle size of the particles constituting the powder was too small, so the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 1 had low gloss and poor performance uniformity. In Comparative Example 2, the volume average particle size of the particles constituting the powder was too large, so the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 2 had low gloss and poor performance uniformity. In Comparative Example 3, the particles constituting the powder did not contain a charge control agent, so the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 3 had low gloss and poor performance uniformity. In Comparative Example 4, the proportion of particles containing the additive A dispersed in a binder resin out of 100 number percent of the particles constituting the powder was less than 5 number percent, so the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 4 had poor electromagnetic wave absorption properties. In Comparative Example 5, the proportion of particles containing the additive A dispersed in the binder resin exceeded 95% by number out of 100% by number of particles constituting the powder, and therefore the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 5 had poor electromagnetic wave absorption properties. In Comparative Example 6, the particles constituting the powder contained the additive A externally added, rather than dispersed in the binder resin, and therefore the electromagnetic wave absorber obtained by melt-molding the powder of Comparative Example 6 had low gloss, poor performance uniformity, and poor electromagnetic wave absorption properties. In Comparative Example 6, the proportion of particles to which the additive A was externally added was 60% by number.

[0171] On the other hand, the powders of Examples 1 to 12 were composed of a plurality of particles containing a binder resin and a charge control agent dispersed in the binder resin, the volume average particle size of the particles being 2 to 100 μm, and 5 to 95% by number of the particles out of 100% by number of the particles constituting the powder contained the additive A dispersed in the binder resin, with the remaining particles not containing additive A. Therefore, the electromagnetic wave absorbers obtained by melt-molding the powders of Examples 1 to 12 had high gloss and excellent performance uniformity, and also had excellent electromagnetic wave absorption properties in the frequency range of 30 to 100 GHz. Furthermore, the binder resin of the powders of Examples 1 to 12 was a thermoplastic resin, and the absolute value of the charge per unit area was 40 to 1500 mC / cm. ２Therefore, the powders were capable of electrostatic adhesion and thermal fixation to a support. It is clear that the powders of each Example can be electrostatically attached to a support, as they have sufficient chargeability, judging from the absolute value of the charge amount per unit area of ​​the powder. It is also clear that the powders of each Example can be thermally fixed to a support, as the surface gloss of the electromagnetic wave absorber obtained by melt-molding the powder is high. The powders of each Example could be electrostatically attached to a support and thermally fixed to a support to form a thin electromagnetic wave absorbing layer.

[0172] The powders of Examples 13 to 20 also consisted of a binder resin and a plurality of particles containing a charge control agent dispersed in the binder resin, the volume average particle size of the particles being 2 to 100 μm, and 5 to 95% by number of the particles out of 100% by number of the particles constituting the powder contained the additive A dispersed in the binder resin, with the remaining particles not containing additive A. Therefore, the electromagnetic wave absorbers obtained by melt-molding the powders of Examples 13 to 20 had high gloss and excellent performance uniformity, and also had excellent electromagnetic wave absorption properties in the frequency range of 30 to 100 GHz. Furthermore, the binder resin contained in the powders of Examples 15 and 16 was a styrene-acrylic resin that contained reactive groups and was therefore thermally crosslinkable, and therefore the binder resin in the electromagnetic wave absorbers produced using the powders of Examples 15 and 16 was thermally crosslinked. The powder of Example 17 contained a silane coupling agent, and therefore the silane coupling agent was thermally crosslinked in the electromagnetic wave absorber produced using the powder of Example 17. The binder resin contained in the powder of Example 20 was a styrene-acrylic resin that was crosslinkable by electron beams due to the inclusion of acryloyl groups introduced by the crosslinkable macromonomer (EBECRYL 820), and therefore the binder resin in the electromagnetic wave absorber produced using the powder of Example 20 was crosslinked by electron beams.

Claims

1. A powder consisting of a plurality of particles containing a binder resin and a charge control agent dispersed in the binder resin, wherein the absolute value of the charge amount per unit area of ​​the powder is 40 to 1500 mC / cm ２ a volume average particle size of the particles is 2 to 100 μm, the binder resin is a thermoplastic resin, and 5 to 95% by number of the particles out of 100% by number of the particles contain additive A, which is at least one selected from the group consisting of carbon nanotubes, carbon nanohorns, and carbon fibers, in a dispersed state in the binder resin, and the remaining particles do not contain additive A.

2. The powder according to claim 1, wherein said additive A is carbon nanotubes.

3. The powder according to claim 2, wherein the carbon nanotubes are single-walled carbon nanotubes.

4. The powder according to claim 1 or 2, wherein the content of the additive A is 0.01 to 2.0 parts by mass relative to 100 parts by mass of the binder resin.

5. The powder according to claim 1 or 2, wherein the charge control agent is a polymer compound.

6. The powder according to claim 1 or 2, wherein the content of additive B, which is at least one selected from the group consisting of amorphous carbon, graphite, graphene, fullerene, metal oxide magnetic material, and metal magnetic material, is less than 12 parts by mass per 100 parts by mass of the binder resin.

7. The powder according to claim 1 or 2, wherein the average circularity of the particles is 0.94 or more.

8. The powder according to claim 1 or 2, wherein the binder resin is at least one selected from the group consisting of styrene-acrylic resins, acrylic resins, and polyester resins.

9. The powder according to claim 1 or 2, wherein the angle of repose of the powder is 15 to 45°.

10. The powder according to claim 1 or 2, wherein the melting temperature (T1 / 2) of the powder by the 1 / 2 method is 110 to 260°C.

11. The powder according to claim 1 or 2, wherein the binder resin further contains a styrene-acrylic resin and a thermoplastic resin different from the styrene-acrylic resin.

12. The powder according to claim 1 or 2, wherein the binder resin comprises a polymer of a polymerizable monomer containing styrene and a (meth)acrylic acid ester, and at least one resin selected from the group consisting of polycarbonate resins and polyester-based resins.

13. The powder according to claim 1 or 2, wherein the binder resin contains a resin that can be crosslinked by heat or electron beams.

14. The powder according to claim 13, wherein the resin crosslinkable by heat or electron beam is a polymer of polymerizable monomers containing styrene, a (meth)acrylic acid ester, and a reactive group-containing monomer.

15. The powder according to claim 14, wherein the reactive group-containing monomer contains at least one selected from the group consisting of epoxy group-containing monomers and hydrolyzable silyl group-containing monomers.

16. The powder according to claim 13, wherein the resin crosslinkable by heat or electron beam is a polymer of polymerizable monomers containing styrene, a (meth)acrylic acid ester, and a crosslinkable macromonomer.

17. The powder according to claim 16, wherein the crosslinkable macromonomer is at least one selected from the group consisting of polymeric compounds containing polymerizable functional groups at multiple ends and polymeric compounds containing a structure containing a butadiene-derived structural unit.

18. The powder according to claim 1 or 2, wherein the particles further contain at least one crosslinkable resin selected from the group consisting of thermosetting resins and electron beam curable resins.

19. The powder according to claim 18, wherein the crosslinkable resin is at least one selected from the group consisting of epoxy resins and maleimide resins.

20. The powder of claim 1 or 2, wherein the particles further comprise a silane coupling agent.

21. An electromagnetic wave absorber comprising a melt-molded product of the powder according to any one of claims 1 to 9 as an electromagnetic wave absorbing layer.

22. An electromagnetic wave absorber comprising a melt-molded product of the powder according to any one of claims 10 to 20 as an electromagnetic wave absorbing layer.

23. A method for producing a molten molded product of the powder, comprising melting the powder according to any one of claims 1 to 20 and cooling the molten powder.

24. A method for producing a melt-molded product of the powder, comprising melting the powder according to any one of claims 13 to 17, thermally crosslinking the crosslinkable resin contained in the molten powder, and then cooling the molten powder.

25. A method for producing a melt-molded product of the powder, comprising melting the powder according to any one of claims 13 to 17, cooling the molten powder to obtain a molded product, and then crosslinking the crosslinkable resin contained in the molded product with an electron beam.

26. A method for producing a molten molded product of the powder, comprising melting the powder according to claim 18 or 19, crosslinking the crosslinkable resin contained in the molten powder by heat, and then cooling the molten powder.

27. A method for producing a molten molded product of the powder, comprising melting the powder according to claim 18 or 19, cooling the molten powder to obtain a molded product, and then crosslinking the crosslinkable resin contained in the molded product with an electron beam.

28. A method for producing a molten molded product of the powder, comprising melting the powder described in claim 20, thermally crosslinking the silane coupling agent contained in the molten powder, and then cooling the molten powder.

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