Electromagnetic wave absorber

Abstract

To provide a technology that enables an electromagnetic wave absorber using resin foam to exhibit excellent electromagnetic wave absorption characteristics in the high-frequency band. [Solution] An electromagnetic wave absorber is provided, comprising a resin foam and a metal oxide containing carbon nanotubes with an aspect ratio of 6 or more and / or a three-dimensional structure with an aspect ratio of 6 or more, which are contained in the resin foam. The electromagnetic wave absorption amount of the electromagnetic wave absorber according to this technology at 77 GHz is 2 dB or more.

Description

[Technical Field]

[0001] This technology relates to electromagnetic wave absorbers. More specifically, it relates to electromagnetic wave absorbers having a resin foam. [Background technology]

[0002] Foams made from resin components are widely used in various fields, from construction, machinery, and home appliances to transportation, packaging, and even everyday necessities, toys, and general merchandise. Furthermore, various developments are underway to improve quality and add new functions, depending on the specific field and purpose.

[0003] For example, Patent Document 1 describes mixing a required amount of carbon black having specific characteristic values ​​with a substrate made of a predetermined resin component, and setting the density to 0.3 g / cm³. 3 A radio wave absorber has been proposed that exhibits excellent radio wave absorption characteristics, particularly for X-band radio waves, while also being highly space-saving and lightweight, by setting it as follows.

[0004] Furthermore, Patent Document 2 discloses a lightweight radio wave absorber that does not generate toxic gases when burned, formed by creating a porous structure from a rubber composition in which conductive carbon black, a radio wave absorbing material, is mixed with nitrile rubber, which is the raw material rubber.

[0005] Furthermore, for example, Patent Document 3 discloses a radio wave absorber containing a foam, wherein the foam comprises a base material containing an elastomer and nanocarbon dispersed in the foam, and the radio wave absorption band can be changed by setting the nanocarbon content to 5 to 45 parts by mass per 100 parts by mass of the base material. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2004-311586 [Patent Document 2] Japanese Patent Publication No. 2006-73760 [Patent Document 3] Japanese Patent Publication No. 2019-106421 [Overview of the Initiative] [Problems that the invention aims to solve]

[0007] As mentioned above, technologies for electromagnetic wave absorbers using resin foam are being developed, but all of them are technologies for the low to medium frequency band. For example, the electromagnetic wave absorber in Patent Document 1 has effective electromagnetic wave absorption characteristics for electromagnetic waves in the X-band frequency band of 8 to 12.5 GHz, the electromagnetic wave absorber in Patent Document 2 has effective electromagnetic wave absorption characteristics for electromagnetic waves in the frequency band of 5 to 40 GHz, and the electromagnetic wave absorber in Patent Document 3 has effective electromagnetic wave absorption characteristics for electromagnetic waves in the 5.8 GHz frequency band used in ETC (Electronic Toll Collection System), etc.

[0008] In recent years, radar devices using ultra-high frequency electromagnetic waves of around 76-78 GHz have been used in vehicle external environment recognition systems, and improvements in electromagnetic wave absorption performance in the high-frequency band (approximately 65-95 GHz) are also expected.

[0009] Resin foams can be applied to a variety of products due to their flexibility and other physical properties. However, electromagnetic wave absorbers made from resin foams have air pockets, and are generally considered to have inferior electromagnetic wave absorption performance compared to electromagnetic wave absorbers made from unfoamed resins. Therefore, until now, no technology has been developed to enable electromagnetic wave absorbers made from resin foams to exhibit excellent electromagnetic wave absorption characteristics in the high-frequency band (approximately 65-95 GHz).

[0010] Therefore, the main objective of this technology is to provide a method for enabling electromagnetic wave absorbers using resin foam to exhibit excellent electromagnetic wave absorption characteristics in the high-frequency band. [Means for solving the problem]

[0011] The inventors of this application have diligently researched techniques to improve the electromagnetic wave absorption performance in the high-frequency band of electromagnetic wave absorbers using resin foam. As a result, they have succeeded in improving the electromagnetic wave absorption performance in the high-frequency band by using a specific dielectric material, and have completed this technology.

[0012] In other words, this technology first involves a resin foam and, The resin foam contains carbon nanotubes with an aspect ratio of 6 or more and / or metal oxides containing a three-dimensional structure with an aspect ratio of 6 or more, The present invention provides an electromagnetic wave absorber having the following properties. The density of the electromagnetic wave absorber related to this technology is 0.2 g / cm³. 3 The following is possible: Zinc oxide can be used as the metal oxide used in the electromagnetic wave absorber related to this technology. In the electromagnetic wave absorber relating to this technology, the carbon nanotubes and the metal oxide may be used in combination. As the resin foam used in the electromagnetic wave absorber according to this technology, ethylene-propylene-diene rubber (EPDM) and / or polyethylene (PE) foam can be used. [Modes for carrying out the invention]

[0013] The following describes preferred embodiments for implementing this technology. The embodiments described below are examples of typical embodiments of this technology, and any combination of these embodiments is possible. Furthermore, this does not mean that the scope of this technology will be narrowed.

[0014] 1. Electromagnetic wave absorber The electromagnetic wave absorber according to the present technology has a resin foam. The resin foam used in the present technology contains carbon nanotubes with an aspect ratio of 6 or more and / or a metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more. That is, the resin foam used in the present technology is a foam of a foamable resin composition containing carbon nanotubes with an aspect ratio of 6 or more and / or a metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more. The foamable resin composition (hereinafter, also referred to as "composition for producing resin foam") for producing the resin foam used in the present technology can contain a resin, a foaming agent, a crosslinking agent, a foaming aid, a crosslinking accelerator, a crosslinking acceleration aid, a softening agent, a processing aid, and various other components that can be used for the production of the resin foam according to the purpose. Hereinafter, each component will be described in detail.

[0015] (1) Resin As the resin used in the present technology, as long as the functions and effects of the present technology are not impaired, one or more resins that can be used for resin foams can be freely combined and used. In the present technology, the resin is a resin in a broad sense, and in addition to the resin in a narrow sense, it includes rubber, elastomer, etc.

[0016] Examples of the resin in a narrow sense include acrylic resins, polyolefin resins, polyurethane resins, silicone resins, etc.

[0017] Examples of the rubber include ethylene-propylene-diene rubber (EPDM), ethylene-propylene rubber (EPM), silicone rubber, urethane rubber (U), nitrile rubber (NBR), chloroprene rubber (CR), natural rubber (NR), isoprene rubber (IR), styrene-butadiene rubber (SBR), butadiene rubber (BR), 1,2-polybutadiene rubber (1,2-BR), butyl rubber (IIR), chlorosulfonated polyethylene rubber (CSM), acrylic rubber (ACM, ANM), epichlorohydrin rubber (CO, ECO), polysulfide rubber (T), fluorine rubber (FKM), etc.

[0018] Examples of the elastomer include, for example, olefin-based elastomer (TPO), styrene-based elastomer (TPS), polyurethane-based elastomer (TPU), polyester-based elastomer (TPEE), polyvinyl chloride-based elastomer (TPVC), and the like.

[0019] Among these, in the present technology, it is preferable to use one or more resins selected from polyolefin-based resins and ethylene-propylene-diene rubber (EPDM), and it is more preferable to use polyolefin-based resins and ethylene-propylene-diene rubber (EPDM) in combination. As the polyolefin-based resin, it is preferable to use polyethylene (PE).

[0020] (2) Electromagnetic wave absorbing material In the present technology, a specific form of carbon nanotube and / or a specific form of metal oxide are used. These exhibit electromagnetic wave absorption performance as a dielectric material. Further, in the present technology, other materials that can exhibit electromagnetic wave absorption performance may be used as long as the effects and functions of the present technology are not impaired.

[0021] (2-1) Carbon nanotube Carbon nanotube (CNT: Carbon nanotube) is a material in which a six-membered ring network (graphene sheet) made of carbon exhibits a coaxial tubular shape, and there are single-layer ones (single-wall nanotubes) and multi-layer ones (multi-wall nanotubes). In the present technology, both single-layer carbon nanotubes and multi-layer carbon nanotubes can be used, and they can also be used in combination.

[0022] The carbon nanotube used in the present technology is characterized in that the aspect ratio is 6 or more. In the present technology, the aspect ratio of the carbon nanotube is the ratio of the length of the tube axis to the diameter of the tube, and specifically, the aspect ratio of the carbon nanotube = the value calculated by the length of the tube axis / the diameter of the tube.

[0023] The lower limit of the aspect ratio of the carbon nanotubes used in this technology is 6 or higher, but the effects of this technology can be achieved if it is 7 or higher, preferably 8 or higher. The upper limit of the aspect ratio of the carbon nanotubes used in this technology can be freely set as long as it does not impair the action or effects of this technology, but for example, it is 35 or lower, preferably 30 or lower, and more preferably 25 or lower.

[0024] The amount of carbon nanotubes with an aspect ratio of 6 or higher used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of carbon nanotubes with an aspect ratio of 6 or higher in the resin foam manufacturing composition is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of carbon nanotubes with an aspect ratio of 6 or higher within this range, it is possible to further improve the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorber.

[0025] In this technology, the upper limit of the amount of carbon nanotubes with an aspect ratio of 6 or more in the resin foam manufacturing composition is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of carbon nanotubes with an aspect ratio of 6 or more within this range, it is possible to prevent a decrease in the physical properties of the manufactured resin foam. Furthermore, a decrease in foamability can also be suppressed.

[0026] (2-2) Metal Oxides The metal oxide used in this technology is characterized by containing a three-dimensional structure with an aspect ratio of 6 or more. A metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more may have an overall aspect ratio of 6 or more, or it may be a metal oxide that contains, for example, a protruding structure or a convex structure with an aspect ratio of 6 or more as part of its structure.

[0027] Examples of metal oxides containing a three-dimensional structure with an aspect ratio of 6 or more include metal oxides containing a single-crystal structure with an aspect ratio of 6 or more, preferably metal oxides with a needle-like single-crystal structure containing a needle-like structure with an aspect ratio of 6 or more, and more preferably tetrapod-shaped metal oxides containing legs with an aspect ratio of 6 or more.

[0028] As the metal oxide, one or more metal oxides capable of exhibiting electromagnetic wave absorption performance can be freely selected and used, as long as they do not impair the function or effect of this technology. Examples of metal oxides include zinc oxide, magnesium oxide, and lead monoxide. Among these, zinc oxide is preferred in this technology.

[0029] The amount of metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more in the resin foam manufacturing composition is, for example, 0.1 parts by mass or more, preferably 0.3 parts by mass or more, more preferably 0.5 parts by mass or more, and even more preferably 1.0 part by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more within this range, it is possible to further improve the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorber.

[0030] In this technology, the upper limit of the amount of metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more in the resin foam manufacturing composition is, for example, 20 parts by mass or less, preferably 15 parts by mass or less, and more preferably 10 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of metal oxide containing a three-dimensional structure with an aspect ratio of 6 or more within this range, it is possible to prevent a decrease in the physical properties of the manufactured resin foam. Furthermore, a decrease in foamability can also be suppressed.

[0031] In this technology, it is preferable to use carbon nanotubes with an aspect ratio of 6 or higher and metal oxides containing a three-dimensional structure with an aspect ratio of 6 or higher in combination. By using them together, the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorber can be further improved.

[0032] (2-3) Other electromagnetic wave absorbing materials In this technology, other materials capable of exhibiting electromagnetic wave absorption performance may be used, provided that they do not impair the function or effect of this technology. Examples of other materials include conductors, dielectrics, magnetic materials, etc. More specifically, examples include carbon-containing particles such as conductive carbon black; iron, silver, nickel, copper, tin, or alloys thereof; and metal compounds such as copper sulfide, copper iodide, zinc sulfide, and cadmium sulfide.

[0033] (3) Foaming agent A foaming agent can be used in the composition for manufacturing resin foams. As for the foaming agent that can be used in this technology, one or more foaming agents that can be used in resin foams can be freely selected and used, as long as they do not impair the action or effect of this technology.

[0034] Examples of blowing agents that can be used in this technology include organic or inorganic pyrolysis-type chemical blowing agents. Examples of organic blowing agents include nitroso compounds such as N,N'-dinitrosopentamethylenetetramine (DPT), azodicarbonamide (ADCA), azodicarboxylic acid metal salts (such as barium azodicarboxylic acid), azobisisobutyronitrile (AIBN), hydrazodicarbonamide, hydrazine derivatives such as 4,4'-oxybis(benzenesulfonyl hydrazide) and toluenesulfonyl hydrazide (TSH), and semicarbazide compounds such as toluenesulfonyl semicarbazide. Examples of inorganic blowing agents include ammonium carbonate, sodium carbonate, ammonium bicarbonate, sodium bicarbonate, ammonium nitrite, sodium borohydride, and anhydrous monosodium citrate.

[0035] Among these, in this technology, it is preferable to use an organic blowing agent, and among organic blowing agents, it is preferable to use a nitroso compound, and among nitroso compounds, it is preferable to use N,N'-dinitrosopentamethylenetetramine (DPT).

[0036] The amount of foaming agent used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of foaming agent in the resin foam manufacturing composition is, for example, 1.0 part by mass or more, preferably 3.0 parts by mass or more, and more preferably 5.0 parts by mass or more, per 100 parts by mass of resin component. By setting the lower limit of the amount of foaming agent used within this range, foaming properties can be improved, contributing to a further improvement in the electromagnetic wave absorption performance of the manufactured electromagnetic wave absorber.

[0037] In this technology, the upper limit of the amount of foaming agent in the resin foam manufacturing composition is, for example, 25 parts by mass or less, preferably 20 parts by mass or less, and more preferably 15 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of foaming agent used within this range, molding defects due to excessive foaming can be suppressed, and cost reduction can also be achieved.

[0038] (4) Crosslinking agent A crosslinking agent can be used in the composition for manufacturing resin foam. As long as the action and effects of this technology are not impaired, one or more crosslinking agents suitable for use in resin foam can be freely selected and used.

[0039] The crosslinking agent that can be used in this technology is a sulfur-based crosslinking agent for sulfur crosslinking. Examples of sulfur-based crosslinking agents that can be used in this technology include sulfur such as powdered sulfur, oil-treated powdered sulfur, precipitated sulfur, colloidal sulfur, and dispersible sulfur, as well as organic sulfur-containing compounds such as tetramethylthiuram disulfide and N,N-dithiobismorpholine, which can release active sulfur under crosslinking conditions to crosslink rubber. Among these, sulfur is preferred as the sulfur-based crosslinking agent in this technology.

[0040] The amount of crosslinking agent used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of crosslinking agent in the resin foam manufacturing composition is, for example, 0.5 parts by mass or more, preferably 1.0 part by mass or more, and more preferably 1.5 parts by mass or more, per 100 parts by mass of resin component. By setting the lower limit of the amount of crosslinking agent used within this range, the viscosity of the composition can be improved, thereby improving foamability. Furthermore, the mechanical properties such as durability of the manufactured foam can be improved.

[0041] In this technology, the upper limit of the amount of crosslinking agent in the resin foam manufacturing composition is, for example, 10 parts by mass or less, preferably 7 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of crosslinking agent used within this range, it is possible to prevent cracking and other defects from occurring during foaming and to improve moldability.

[0042] (5) Foaming agent A foaming aid can be used in the composition for manufacturing resin foams. As for the foaming aids that can be used in this technology, one or more foaming aids that can be used in resin foams can be freely selected and used, as long as they do not impair the action or effect of this technology.

[0043] Examples of foaming agents that can be used in this technology include urea-based additives such as urea, metal oxides, and fatty acid metal salts. Examples of metal oxides include zinc oxide, zinc chloride, zinc acetate, zinc nitrate, lead oxide, dibasic lead phosphite, and tribasic lead sulfate. Examples of fatty acid metal salts include zinc stearate, lead stearate, magnesium stearate, and calcium stearate. Among these, it is preferable to use urea as a foaming agent in this technology.

[0044] The amount of foaming agent used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of foaming agent in the resin foam manufacturing composition is, for example, 0.5 parts by mass or more, preferably 1.0 part by mass or more, and more preferably 1.5 parts by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of foaming agent used within this range, the foaming properties can be improved by adjusting the foaming rate during manufacturing.

[0045] In this technology, the upper limit of the amount of foaming aid in the resin foam manufacturing composition is, for example, 10 parts by mass or less, preferably 7 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of foaming aid used within this range, it is possible to prevent cracking and other defects during foaming and improve moldability.

[0046] (6) Crosslinking promoter A crosslinking accelerator can be used in the composition for manufacturing resin foams. As long as the action and effects of this technology are not impaired, one or more crosslinking accelerators suitable for use in resin foams may be freely selected and used.

[0047] Examples of crosslinking accelerators that can be used in this technology include thiazoles (e.g., 2-mercaptobenzothiazole, dibenzothiadyl disulfide, etc.), thiurams (e.g., tetramethylthiuram disulfide, tetramethylthiuram monosulfide, etc.), dithiocarbamates (e.g., sodium dimethyldithiocarbamate, sodium diethyldithiocarbamate, zinc dimethyldithiocarbamate, zinc diethyldithiocarbamate, etc.), guanidines (e.g., diphenylguanidine, di-o-tolylguanidine, etc.), sulfenamides (e.g., Examples of crosslinking accelerators include benzothiazyl-2-diethylsulfenamide, N-cyclohexyl-2-benzothiadylsulfenamide, xanthogenic acids (e.g., sodium isopropylxanthogenic acid, zinc isopropylxanthogenic acid), ammonium aldehydes (e.g., ammonium acetaldehyde, hexamentylenetetramine), aldehyde amines (e.g., n-butyraldehyde aniline, monobutylamine), thioureas (e.g., diethylthiourea, trimethylthiourea), and dithiophosphide crosslinking accelerators. Among these, in this technology, thiazoles and thiurams are preferred as crosslinking accelerators from the viewpoint of adjusting the timing of foaming rate and vulcanization rate.

[0048] The amount of crosslinking accelerator used in the resin foam manufacturing composition can be freely set as long as it does not impair the action and effects of this technology. In this technology, the lower limit of the amount of crosslinking accelerator in the resin foam manufacturing composition is, for example, 0.1 parts by mass or more, preferably 0.5 parts by mass or more, and more preferably 1.0 part by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of crosslinking accelerator used within this range, the crosslinking rate can be increased, gas leakage can be suppressed, and foaming properties during manufacturing can be improved. Furthermore, the mechanical properties of the rubber foam can be improved.

[0049] In this technology, the upper limit of the amount of crosslinking accelerator in the resin foam manufacturing composition is, for example, 10 parts by mass or less, preferably 7 parts by mass or less, and more preferably 5 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of crosslinking accelerator used within this range, it is possible to prevent the crosslinking rate from becoming too high, which would result in unfoamed foam, and to improve moldability.

[0050] (7) Crosslinking aids A crosslinking accelerator can be used in the composition for manufacturing resin foams. As long as the action and effects of this technology are not impaired, one or more crosslinking accelerators suitable for use in resin foams may be freely selected and used.

[0051] Examples of crosslinking accelerators that can be used in this technology include metal oxides such as zinc oxide (activated zinc oxide) and magnesium oxide. Among these, zinc oxide is preferred as the crosslinking accelerator in this technology from the viewpoint of adjusting the timing of foaming rate and vulcanization rate.

[0052] The amount of crosslinking accelerator used in the resin foam manufacturing composition can be freely set as long as it does not impair the action and effects of this technology. In this technology, the lower limit of the amount of crosslinking accelerator in the resin foam manufacturing composition is, for example, 1.0 part by mass or more, preferably 1.5 parts by mass or more, and more preferably 2.0 parts by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of crosslinking accelerator used within this range, the crosslinking rate can be increased, gas leakage can be suppressed, and foaming properties during manufacturing can be improved. Furthermore, the mechanical properties of the rubber foam can be improved.

[0053] In this technology, the upper limit of the amount of crosslinking accelerator in the resin foam manufacturing composition is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, and more preferably 8 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of crosslinking accelerator used within this range, it is possible to prevent the crosslinking rate from becoming too high, which would result in unfoamed foam, and to improve moldability.

[0054] (8) Moisturizer A softening agent can be used in the composition for manufacturing resin foam. As for the softening agent that can be used in this technology, one or more softening agents that can be used in resin foam can be freely selected and used, as long as they do not impair the action or effect of this technology.

[0055] Examples of softening agents that can be used in this technology include process oil, paraffin wax, liquid paraffin, rosin, chroman resin, polybutene, asphalt, and plasticizers. Among these, process oil is preferred as the softening agent in this technology.

[0056] The amount of softener used in the resin foam manufacturing composition can be freely set as long as it does not impair the function and effects of this technology. In this technology, the lower limit of the amount of softener in the resin foam manufacturing composition is, for example, 10 parts by mass or more, preferably 15 parts by mass or more, and more preferably 20 parts by mass or more, per 100 parts by mass of resin component. By setting the lower limit of the amount of softener used within this range, it is possible to manufacture resin foams with lower hardness.

[0057] In this technology, the upper limit of the amount of softener in the resin foam manufacturing composition is, for example, 45 parts by mass or less, preferably 40 parts by mass or less, and more preferably 35 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of softener used within this range, the kneadability during manufacturing can be improved.

[0058] (9) Processing aids Processing aids can be used in the composition for manufacturing resin foams. As processing aids that can be used in this technology, one or more processing aids that can be used in resin foams can be freely selected and used, as long as they do not impair the action or effect of this technology.

[0059] Examples of processing aids that can be used in this technology include fatty acids such as stearic acid, fatty acid esters, fatty acid amides, aliphatic alcohols, and metal salts of fatty acids. Among these, it is preferable to use fatty acids such as stearic acid or fatty acid esters as processing aids in this technology.

[0060] The amount of processing aid used in the resin foam manufacturing composition can be freely set as long as it does not impair the action and effects of this technology. In this technology, the lower limit of the amount of processing aid in the resin foam manufacturing composition is, for example, 1.0 part by mass or more, preferably 2.0 parts by mass or more, and more preferably 3.0 parts by mass or more, per 100 parts by mass of the resin component. By setting the lower limit of the amount of processing aid used within this range, the kneading processability during manufacturing can be further improved.

[0061] In this technology, the upper limit of the amount of processing aid in the resin foam manufacturing composition is, for example, 15 parts by mass or less, preferably 10 parts by mass or less, and more preferably 7.0 parts by mass or less, per 100 parts by mass of the resin component. By setting the upper limit of the amount of processing aid used within this range, it is possible to prevent a decrease in the strength of the manufactured rubber foam.

[0062] (10) Other ingredients In the composition for manufacturing resin foam, one or more components that can be used in resin foam may be freely selected and used as other components, depending on the purpose, as long as they do not impair the function or effect of this technology.

[0063] Examples of components that can be used in the resin foam according to this technology include foam stabilizers, fillers, stabilizers, colorants, pigments, antioxidants, dispersants, UV absorbers, and flame retardants.

[0064] (11) Method for manufacturing resin foam The resin foam used in this technology can be manufactured by freely selecting a general resin foam manufacturing method. For example, the resin foam can be manufactured by performing a composition preparation step to prepare a resin foam manufacturing composition, a crosslinking foaming step to crosslink and foam the prepared resin foam manufacturing composition, a molding step, and so on.

[0065] [Composition preparation process] The composition preparation step is the process of kneading the raw materials for the resin foam manufacturing composition described above. Specifically, all or part of the raw materials for the resin foam manufacturing composition can be kneaded using a kneader, Banbury, roll, or other kneading machine.

[0066] The composition preparation process can also be carried out in multiple stages. Specifically, for example, the ingredients other than the crosslinking agent, crosslinking accelerator, foaming agent, foaming aid, etc., can be kneaded first, and then the crosslinking agent, crosslinking accelerator, crosslinking accelerator aid, foaming agent, foaming aid, etc., can be added to the resulting primary mixture and kneaded in a secondary manner.

[0067] [Cross-linked foaming process] The crosslinking and foaming process is a process of crosslinking and foaming the prepared resin foam manufacturing composition. Specifically, crosslinking and foaming can be carried out, for example, under heating and, if necessary, pressurization.

[0068] The crosslinking foaming process can also be carried out in multiple stages. Specifically, for example, after performing a first crosslinking foam under first heating (and pressurizing if necessary) conditions, the resulting primary crosslinked foam can be subjected to a second crosslinking foam under second heating (and pressurizing if necessary) conditions, thus allowing for crosslinking and foaming to be carried out in multiple stages.

[0069] [Molding process] The shaping process is a process of processing the resin foam that has undergone the cross-linking and foaming process described above by ear-cutting or slicing it into a desired form. The specific method of the shaping process is not particularly limited as long as the functions and effects of the present technology are not impaired, and shaping methods that can be used in the production of general resin foams can be freely combined and used.

[0070] (12) Physical properties of the resin foam [Density] The density of the resin foam used in the present technology can be freely set as long as the functions and effects of the present technology are not impaired. As the lower limit value of the density of the resin foam used in the present technology, for example, 0.05 g / cm 3 or more, preferably 0.08 g / cm 3 or more, more preferably 0.1 g / cm 3 or more. By setting the lower limit value of the density of the resin foam within this range, it is possible to prevent electromagnetic waves from passing through. As the upper limit value of the density of the resin foam used in the present technology, for example, 1.0 g / cm 3 or less, preferably 0.8 g / cm 3 or less, more preferably 0.5 g / cm 3 or less, still more preferably 0.3 g / cm 3 or less, particularly preferably 0.2 g / cm 3 or less. By setting the upper limit value of the density of the resin foam within this range, the electromagnetic wave absorption performance can be improved. In the present technology, the density is a value measured in accordance with the method based on JIS K6767:1999.

[0071] [Expansion ratio] The foaming ratio of the resin foam used in this technology can be freely set as long as it does not impair the function or effect of this technology. The lower limit of the foaming ratio of the resin foam used in this technology is, for example, greater than 1.0 times, preferably 1.1 times or more, more preferably 1.5 times or more, and even more preferably 2.0 times or more. By setting the lower limit of the foaming ratio of the resin foam within this range, the electromagnetic wave absorption performance can be improved. The upper limit of the foaming ratio of the resin foam used in this technology is, for example, 15 times or less, preferably 13 times or less, and more preferably 10 times or less. By setting the upper limit of the foaming ratio of the resin foam within this range, it is possible to prevent electromagnetic waves from being transmitted. In this technology, the foaming ratio of the resin foam is the value calculated by the method described in the examples below.

[0072] [Cell type] The cell morphology of the resin foam used in this technology is not particularly limited, as long as it does not impair the function or effect of this technology, but it is preferable that it has closed cells. Having closed cells can contribute to further improvement of the electromagnetic wave absorption performance of the electromagnetic wave absorber. The mechanism by which the electromagnetic wave absorber in this technology achieves high electromagnetic wave absorption performance has not been elucidated, but it is presumed that electromagnetic waves are attenuated while undergoing multiple scattering within the closed cells of the foam.

[0073] 2. Performance of electromagnetic wave absorbers The electromagnetic wave absorber related to this technology is characterized by having excellent electromagnetic wave absorption characteristics in the high-frequency band (approximately 65 to 95 GHz).

[0074] More specifically, the amount of electromagnetic wave absorption at 77 GHz, measured by the free-space method, is, for example, 2 dB or more, preferably 3 dB or more, and more preferably 4 dB or more. Having such electromagnetic wave absorption characteristics makes it possible to reduce electromagnetic interference in the high-frequency band.

[0075] Furthermore, this technology can also take the following forms. [1] Resin foam and, The resin foam contains carbon nanotubes with an aspect ratio of 6 or more and / or metal oxides containing a three-dimensional structure with an aspect ratio of 6 or more, An electromagnetic wave absorber having the following properties. [2] Density is 0.2 g / cm³ 3 The electromagnetic wave absorber described in [1] is as follows: [3] The electromagnetic wave absorber according to [1] or [2], wherein the metal oxide is zinc oxide. [4] An electromagnetic wave absorber according to any one of [1] to [3], comprising the carbon nanotube and the metal oxide in combination. [5] The electromagnetic wave absorber according to any one of [1] to [4], wherein the resin foam is a foam of ethylene-propylene-diene rubber (EPDM) and / or polyethylene (PE). [Examples]

[0076] The present technology will be described in more detail below based on the following examples. The examples described below are representative examples of the present technology and should not be interpreted as narrowing the scope of the present technology.

[0077] (1) Manufacturing of electromagnetic wave absorbers [Examples 1-3] The raw materials shown in Table 1 were mixed, roll-kneaded, and then heated under the conditions shown in Table 1 to perform primary cross-linking foaming and secondary cross-linking foaming to produce an electromagnetic wave absorber with a thickness of 2 mm.

[0078] [Comparative Examples 1 and 2] A 2mm thick electromagnetic wave absorber was manufactured by mixing the raw materials shown in Table 1, rolling the mixture, and then heating it under the conditions shown in Table 1 to perform primary crosslinking (comparative example 2 was crosslinked foaming).

[0079] (2) Measurement of physical properties The electromagnetic wave absorbers manufactured were evaluated for their various properties using the following methods.

[0080] [density] Density was measured in accordance with the method based on JIS K6767:1999.

[0081] [Expansion ratio] The expansion ratio was calculated using the formula: Expansion ratio (times) = Density before expansion / Density after expansion.

[0082] [Electromagnetic wave absorption amount] The amount of electromagnetic wave absorption at 77 GHz was measured using the free-space method.

[0083] (3) Results The results are shown in Table 1 below. [Table 1]

[0084] (4) Discussion As shown in Table 1, Examples 1-3, which used carbon nanotubes with an aspect ratio of 6 or higher and / or metal oxides containing a three-dimensional structure with an aspect ratio of 6 or higher, exhibited excellent electromagnetic wave absorption performance at 77 GHz.

Claims

1. Resin foam and, The resin foam contains carbon nanotubes with an aspect ratio of 6 or more and / or metal oxides containing a three-dimensional structure with an aspect ratio of 6 or more, An electromagnetic wave absorber having the following properties.

2. Density is 0.2 g / cm³ ３ The electromagnetic wave absorber according to claim 1, which is as follows:

3. The electromagnetic wave absorber according to claim 1, wherein the metal oxide is zinc oxide.

4. The electromagnetic wave absorber according to claim 1, wherein the carbon nanotube and the metal oxide are used in combination.

5. The electromagnetic wave absorber according to claim 1, wherein the resin foam is a foam of ethylene-propylene-diene rubber (EPDM) and / or polyethylene (PE).

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