Ink set for forming radio wave absorber, mixture for forming radio wave absorber, method for manufacturing radio wave absorber, and radio wave absorber

Abstract

Provided is an ink set for forming a radio wave absorber, the ink set including a first ink containing a main agent and a second ink containing a curing agent, wherein at least one of the first ink and the second ink contains a filler.

Description

Ink set for forming radio wave absorber, mixture for forming radio wave absorber, method for producing radio wave absorber, and radio wave absorber

[0001] The present invention relates to an ink set for forming a radio wave absorber, a mixture for forming a radio wave absorber, a method for producing a radio wave absorber, and a radio wave absorber. Specifically, the present invention relates to an ink set for forming a radio wave absorber, a mixture for forming a radio wave absorber, a method for producing a radio wave absorber, and a radio wave absorber that have excellent long-term storage stability and allow users to easily produce a radio wave absorber.

[0002] In modern society, radio waves are used in a variety of fields, including broadcasting, communications, medicine, chemical analysis, positioning, remote control, etc. For example, millimeter-wave radar, which uses radio waves in the frequency band of 30 GHz to 300 GHz, is one of the key technologies that supports autonomous driving of vehicles.

[0003] Millimeter-wave radar uses radio waves in the above frequency bands to measure the distance, speed, and angle to an object. Taking autonomous driving, one of the technologies in use, as an example, with the spread of ADAS (Advanced Driver Assistance Systems), millimeter-wave radars with a frequency of 76 GHz to 79 GHz, which can detect long distances, are being used as forward-monitoring radars. Millimeter-wave radars emit millimeter waves and receive the millimeter waves reflected by the object using a receiving antenna to detect the distance to the object, etc.

[0004] In millimeter-wave radar devices, a shielding member that blocks radio waves is provided between the antenna and the control circuit. This prevents a decrease in detection accuracy due to reception of millimeter waves reflected by objects other than the target (such as the road surface). For example, Patent Documents 1 and 2 disclose molded bodies and compositions containing resin and carbon fiber as shielding members.

[0005] JP 2019-161208 A JP 2020-111730 A

[0006] Radio wave absorbers are generally manufactured by mixing a base agent, a curing agent, and a filler. Once mixed, the mixture begins to harden, making it unsuitable for long-term storage. Furthermore, the filler in powder form is not easy to handle, and weighing it requires environmental measures such as static electricity and humidity control. This makes it difficult for users to easily manufacture radio wave absorbers.

[0007] An object of the present invention is to provide an ink set for forming a radio wave absorber, a mixture for forming a radio wave absorber, a method for producing a radio wave absorber, and a radio wave absorber which have excellent long-term storage properties and allow a user to easily produce a radio wave absorber.

[0008] As a result of extensive research, the present inventors have found that the use of a specific ink set provides excellent long-term storage stability and allows users to easily produce a radio wave absorber, and have thus completed the present invention. According to the present invention, the following ink sets for forming a radio wave absorber and the like can be provided. 1. An ink set for forming a radio wave absorber comprising a first ink containing a base agent and a second ink containing a curing agent, wherein a filler is contained in at least one of the first ink and the second ink. 2. The ink set for forming a radio wave absorber according to 1, wherein the filler is contained in only one of the first ink and the second ink. 3. The ink set for forming a radio wave absorber according to 1 or 2, wherein the filler is contained only in the first ink. 4. The ink set for forming a radio wave absorber according to 1, wherein the filler is contained in both the first ink and the second ink. 5. 5. The ink set for forming a radio wave absorber according to any one of 1 to 4, wherein the condition of 0≦B / (A+B)≦0.75 is satisfied when the mass of the filler contained in the first ink is A mass % and the mass of the filler contained in the second ink is B mass % relative to 100% by mass of the total mass of the first ink and the second ink. 6. The ink set for forming a radio wave absorber according to any one of 1 to 5, wherein the condition of A+B≦20 mass % is satisfied when the mass of the filler contained in the first ink is A mass % and the mass of the filler contained in the second ink is B mass % relative to 100% by mass of the total mass of the first ink and the second ink. 7. The ink set for forming a radio wave absorber according to any one of 1 to 6, wherein the mass of the filler contained in the first ink is 0 to 20 mass % relative to 100% by mass of the total mass of the first ink and the second ink. 8. 8. The ink set for forming a radio wave absorber according to any one of 1 to 7, wherein the mass of the filler contained in the second ink is 0 to 20 mass% relative to 100 mass% of the total mass of the first ink and the second ink. 9. The ink set for forming a radio wave absorber according to any one of 1 to 8, wherein the mass of the filler is 0 to 25 mass% relative to 100 mass% of the first ink. 10. The ink set for forming a radio wave absorber according to any one of 1 to 9, wherein the mass of the filler is 0 to 70 mass% relative to 100 mass% of the second ink.11. The ink set for forming a radio wave absorber according to any one of 1 to 10, wherein the base agent comprises polydimethylsiloxane. 12. The ink set for forming a radio wave absorber according to any one of 1 to 11, wherein the filler comprises one or more species selected from the group consisting of carbon particles and carbon fibers. 13. The ink set for forming a radio wave absorber according to any one of 1 to 12, wherein the filler comprises carbon particles and carbon fibers. 14. The ink set for forming a radio wave absorber according to any one of 1 to 13, wherein the viscosity of the base agent at 25°C is 10,000 cP or less. 15. A mixture for forming a radio wave absorber, which is a mixture of the first ink and the second ink of the ink set for forming a radio wave absorber according to any one of 1 to 14. 16. A method for producing a radio wave absorber, which comprises mixing the first ink and the second ink of the ink set for forming a radio wave absorber according to any one of 1 to 14. 17. The method for producing a radio wave absorber according to 16, wherein the standard deviation of the film thickness of the obtained radio wave absorber is 15 μm or less. 18. 19. A radio wave absorber produced using the ink set for forming a radio wave absorber according to any one of 1 to 14 or the mixture according to 15. 19. The radio wave absorber according to 18, which has a film thickness standard deviation of 15 μm or less.

[0009] According to the present invention, it is possible to provide an ink set for forming a radio wave absorber, a mixture for forming a radio wave absorber, a method for producing a radio wave absorber, and a radio wave absorber which have excellent long-term storage properties and allow a user to easily produce a radio wave absorber.

[0010] The ink set for forming a radio wave absorber, the mixture for forming a radio wave absorber, the method for producing a radio wave absorber, and the radio wave absorber of the present invention will be described in detail below. In this specification, "x to y" represents a numerical range of "not less than x and not more than y." The upper and lower limit values ​​described for numerical ranges can be combined arbitrarily. Furthermore, among the individual embodiments of the aspects of the present invention described below, it is possible to combine two or more embodiments that are not mutually contradictory, and an embodiment combining two or more embodiments is also an embodiment of the aspects of the present invention.

[0011] 1. Ink set for forming a radio wave absorber An ink set for forming a radio wave absorber according to one aspect of the present invention is an ink set for forming a radio wave absorber, comprising a first ink containing a base agent and a second ink containing a curing agent, wherein at least one of the first ink and the second ink contains a filler.

[0012] The ink set for forming a wave absorber according to this embodiment (sometimes simply referred to as an "ink set") is used to form a wave absorber by mixing a first ink and a second ink and curing the resulting mixture. The ink set according to this embodiment has excellent long-term storage stability and allows users to easily produce a wave absorber. More specifically, according to this embodiment, the first ink and the second ink are provided as separate entities, preventing curing and providing excellent long-term storage stability even when the filler is included. Conventionally, when producing a wave absorber, the amount of filler to be contained in the wave absorber is measured. However, filler in powder form is difficult to handle, and weighing requires environmental measures against static electricity and humidity. In contrast, according to this embodiment, the filler is contained in at least one of the first ink and the second ink constituting the ink set. This makes handling easy for users (the operation of weighing the filler in powder form and mixing it with the ink can be omitted), allowing users to easily produce a wave absorber. Furthermore, because the amount of filler can be accurately adjusted, the wave absorber can be imparted with intended performance (e.g., performance set by the manufacturer, etc.) with high precision. Although the details will be described later, by having the manufacturer or the like instruct the user on the blending ratio (or blending amounts) of the first ink and the second ink, the user can easily manufacture a radio wave absorber having the intended performance (performance set by the manufacturer or the like).

[0013] In one embodiment, the filler is contained in only one of the first ink and the second ink, which eliminates the need for manufacturers to weigh and mix the filler for each of the first ink and the second ink, thereby improving productivity of the ink set.

[0014] In one embodiment, the filler is contained only in the first ink. In this case, since the second ink does not contain a filler, deterioration of the performance of the curing agent due to the filler or impurities contained in the filler can be suppressed. Furthermore, this effect becomes more pronounced the longer the storage period. As a result, when the first ink and the second ink are mixed, the curing agent can be made to act favorably on the base agent, resulting in a good cured state of the radio wave absorber.

[0015] In one embodiment, a filler is contained in both the first ink and the second ink. Although the viscosity of the ink increases when a filler is blended, by including a filler in both the first ink and the second ink, it is possible to prevent the viscosity of only one of the inks from increasing. This improves the mixability of the first ink and the second ink, and the uniformity of the film thickness of the obtained radio wave absorber can be increased and the standard deviation can be reduced.

[0016] In one embodiment, when the total mass of the first ink and the second ink is 100% by mass, the mass of the filler contained in the first ink is A% by mass, and the mass of the filler contained in the second ink is B% by mass, the condition 0≦B / (A+B)≦0.75 is satisfied. This makes it possible to improve film formability when forming a radio wave absorber, and to reduce the standard deviation of the film thickness of the radio wave absorber. In one embodiment, the value of B / (A+B) is 0 or more, 0.01 or more, 0.02 or more, 0.05 or more, 0.07 or more, or 0.10 or more, and is also 0.95 or less, 0.90 or less, 0.85 or less, 0.80 or less, 0.75 or less, 0.74 or less, 0.73 or less, 0.72 or less, 0.71 or less, 0.70 or less, 0.69 or less, 0.68 or less, 0.67 or less, 0.66 or less, 0.65 or less, 0.64 or less, 0.63 or less, 0.62 or less, 0.61 or less, 0.60 or less, 0.59 or less, 0.58 or less, 0.57 or less, 0.56 or less, 0.55 or less, 0.54 or less, 0.53 or less, 0.52 or less, 0.51 or less, 0.50 or less, 0.49 or less, 0.48 or less, 0.47 or less, 0.46 or less, 0.45 or less, 0.44 or less, 0.43 or less, 0.42 or less, 0.41 or less, 0.40 or less, 0.39 or less, 0.38 or less, 0.37 or less, 0.36 or less, 0.35 or less, 0.34 or less, 0.33 or less, 0.32 or less, 0.31 or less, 0.30 or less, 0.29 or less, 0.28 or less, 0.27 or less, 0.26 or less, 0.25 or less, 0.24 or less, 0.23 or less, 0.22 or less, 0.21 or less, 0.20 or less, or 0.15 or less. A small value of B / (A+B) makes it easier to obtain a radio wave absorber having a small film thickness standard deviation. The value of B / (A+B) is preferably 0.75 or less, more preferably 0.70 or less, and particularly preferably 0.50 or less. In one embodiment, the value of B / (A+B) is 0 to 0.75, 0.01 to 0.73, 0.01 to 0.70, 0.01 to 0.65, 0.02 to 0.60, 0.05 to 0.50, 0.07 to 0.45, or 0.10 to 0.40.

[0017] In one embodiment, when the total mass of the first ink and the second ink is 100% by mass, the mass of the filler contained in the first ink is A% by mass, and the mass of the filler contained in the second ink is B% by mass, the condition A + B ≦ 20% by mass is satisfied. This can improve film-forming properties when forming a radio wave absorber, reduce the standard deviation of the film thickness of the radio wave absorber, and improve the cured state. In one embodiment, A + B is 20% by mass or less, 15% by mass or less, or 10% by mass or less, or 1% by mass or more, 3% by mass or more, or 5% by mass or more. In one embodiment, A + B is 1 to 20% by mass, 3 to 15% by mass, or 5 to 10% by mass. The value of A + B can be appropriately adjusted (preferably within the range of A + B ≦ 20% by mass). While the value of A + B can affect the characteristics of the radio wave absorber, according to this embodiment, the value of A + B can be accurately adjusted, thereby imparting desired characteristics to the radio wave absorber with high precision. It is particularly preferable that both the conditions 0≦B / (A+B)≦0.75 and A+B≦20% by mass are satisfied.

[0018] In one embodiment, the mass A (% by mass) of the filler contained in the first ink is 0% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, or 4% by mass or more, and is 20% by mass or less, 18% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, 9% by mass or less, 8% by mass or less, or 7% by mass or less, relative to the total mass (100% by mass) of the first ink and the second ink. This provides the effect of imparting the intended performance to the radio wave absorber with higher precision. In one embodiment, the mass A (% by mass) of the filler contained in the first ink is 0 to 20% by mass, 0 to 18% by mass, 1 to 15% by mass, 1 to 12% by mass, 2 to 10% by mass, 2 to 9% by mass, 3 to 8% by mass, or 4 to 7% by mass, relative to the total mass (100% by mass) of the first ink and the second ink.

[0019] In one embodiment, the mass B of the filler contained in the second ink, relative to the total mass of the first ink and the second ink (100% by mass), is 0% by mass or more or 0.5% by mass or more, and is 20% by mass or less, 19% by mass or less, 18% by mass or less, 17% by mass or less, 16% by mass or less, 15% by mass or less, 14% by mass or less, 13% by mass or less, 12% by mass or less, 11% by mass or less, 10% by mass or less, 9% by mass or less, 8% by mass or less, 7% by mass or less, 6% by mass or less, 5% by mass or less, 4% by mass or less, 3% by mass or less, 2% by mass or less, or 1% by mass or less. This provides the effect of imparting the intended performance to the radio wave absorber with higher precision. In one embodiment, the mass B (mass %) of the filler contained in the second ink, relative to the total mass of the first ink and the second ink (100 mass %), is 0 to 20 mass %, 0 to 19 mass %, 0 to 18 mass %, 0 to 17 mass %, 0 to 16 mass %, 0 to 15 mass %, 0 to 14 mass %, 0 to 13 mass %, 0 to 12 mass %, 0 to 11 mass %, 0.5 to 10 mass %, 0 to 9 mass %, 0 to 8 mass %, 0 to 7 mass %, 0.5 to 6 mass %, 0.5 to 5 mass %, 0.5 to 4 mass %, 0.5 to 3 mass %, 0.5 to 2 mass %, or 0.5 to 1 mass %.

[0020] In one embodiment, the mass of the filler, relative to 100% by mass of the first ink, is 0% by mass or more, 1% by mass or more, 2% by mass or more, or 3% by mass or more, and is 25% by mass or less, 23% by mass or less, 20% by mass or less, 18% by mass or less, 15% by mass or less, 12% by mass or less, 10% by mass or less, 8% by mass or less, or 5% by mass or less. This provides the effect of imparting the intended performance to the radio wave absorber with higher precision. In one embodiment, the mass of the filler, relative to 100% by mass of the first ink, is 0 to 25% by mass, 0 to 23% by mass, 0 to 20% by mass, 1 to 18% by mass, 1 to 15% by mass, 2 to 12% by mass, 2 to 10% by mass, 3 to 8% by mass, or 3 to 5% by mass.

[0021] In one embodiment, the mass of the filler relative to 100% by mass of the second ink is 0% by mass or more, 1% by mass or more, 2% by mass or more, 3% by mass or more, 4% by mass or more, or 5% by mass or more, and is 70% by mass or less, 65% by mass or less, 60% by mass or less, 55% by mass or less, 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, 20% by mass or less, 15% by mass or less, or 10% by mass or less. This provides the effect of imparting the intended performance to the radio wave absorber with higher precision. In one embodiment, the mass of the filler is 0 to 70 mass%, 0 to 65 mass%, 0 to 60 mass%, 1 to 55 mass%, 1 to 50 mass%, 2 to 45 mass%, 2 to 40 mass%, 3 to 35 mass%, 3 to 30 mass%, 4 to 25 mass%, 4 to 20 mass%, 5 to 15 mass%, or 5 to 10 mass%, relative to 100 mass% of the mass of the second ink.

[0022] In one embodiment, the amount of filler contained in each of the first ink and the second ink is adjusted so that the difference in viscosity between the first ink and the second ink is small, more preferably so that the viscosities are equivalent. It is more preferable to perform such adjustment within a range that satisfies at least one of the above-mentioned conditions 0≦B / (A+B)≦0.75 and A+B≦20 mass %, and preferably both of these conditions. This improves the mixability of the first ink and the second ink, and makes it possible to further reduce the standard deviation of the film thickness of the resulting radio wave absorber.

[0023] In one embodiment, the mass ratio between the first ink and the second ink (mass of the first ink / mass of the second ink) is 0.5 or more, 0.8 or more, or 1.0 or more, and is 20 or less, 15 or less, or 10 or less. This has the effect of enabling the formation of a more satisfactorily cured cured film. In one embodiment, the mass ratio between the first ink and the second ink (mass of the first ink / mass of the second ink) is 0.5 to 20, 0.8 to 15, or 1.0 to 10.

[0024] In one embodiment, the mass ratio of the main agent contained in the first ink to the curing agent contained in the second ink (mass of the main agent contained in the first ink / mass of the curing agent contained in the second ink) is 0.8 or more, 0.9 or more, or 1.0 or more, and is 18 or less, 15 or less, or 10 or less. This has the effect of enabling the formation of a more satisfactorily cured cured film. In one embodiment, the mass ratio of the main agent contained in the first ink to the curing agent contained in the second ink (mass of the main agent contained in the first ink / mass of the curing agent contained in the second ink) is 0.8 to 18, 0.9 to 15, or 1.0 to 10.

[0025] (Base Material) In this specification, the "base material" contained in the first ink includes all components other than the filler that may be contained in the first ink. The base material may include a resin. Examples of resins include thermoplastic resins and thermosetting resins. Thermosetting resins are preferred because their dielectric constants can be easily adjusted. Specific examples include silicone resins, epoxy resins, phenolic resins, polyurethane resins, thermosetting polyimides, unsaturated polyester resins, and alkyd resins. These resins may be used alone or in combination of two or more. Among these resins, silicone resins are preferred. As the silicone resin, siloxane (a resin having a siloxane bond, also known as polysiloxane) is preferred, with organopolysiloxane being more preferred, and polydimethylsiloxane being particularly preferred. When the base material includes polydimethylsiloxane, the effect of obtaining a radio wave absorber with high flexibility and durability is achieved. The mass of the resin relative to 100% by mass of the base resin is not particularly limited, but is preferably 60 to 100% by mass, more preferably 70 to 100% by mass, and even more preferably 80 to 100% by mass. This provides the effect of suppressing variations in the dielectric constant. The base resin may also contain an amount of resin such that the viscosity of the base resin at 25°C is as follows:

[0026] In one embodiment, the viscosity of the base resin at 25°C is 10,000 cP or less. This has the effect of facilitating appropriate mixing of the filler. In one embodiment, the viscosity of the base resin at 25°C is 10,000 cP or less, 9,800 cP or less, or 9,500 cP or less, or 100 cP or more, or 500 cP or more. In one embodiment, the viscosity of the base resin at 25°C is 100 to 10,000 cP, 100 to 9,800 cP, or 500 to 9,500 cP. The viscosity of the base resin at 25°C is a value measured using a general Brookfield viscometer.

[0027] The base material may contain a resin and a solvent. The solvent is not particularly limited, and examples thereof include xylene, ethylbenzene, etc. The mass of the solvent is not particularly limited, and is, for example, less than 1 mass%, relative to 100 mass% of the base material.

[0028] (Curing Agent) In this specification, the "curing agent" contained in the second ink includes all components other than the filler that may be contained in the second ink. The curing agent may include a component capable of curing the resin contained in the first ink. For example, when polydimethylsiloxane is used as the resin contained in the first ink, a hydrosilylation reaction catalyst or the like may be used as the "component capable of curing the resin contained in the first ink." The mass of the "component capable of curing the resin contained in the first ink" is not particularly limited, but is preferably 70 to 100% by mass, more preferably 80 to 100% by mass, and even more preferably 90 to 100% by mass, per 100% by mass of the curing agent. This effectively suppresses curing problems. The curing agent may include a "component capable of curing the resin contained in the first ink" and a solvent. The solvent is not particularly limited, and examples include xylene and ethylbenzene. The mass of the solvent is not particularly limited, and is, for example, less than 1% by mass, per 100% by mass of the curing agent.

[0029] (Filler) The filler contained in at least one of the first ink and the second ink may be an electromagnetic wave loss material. Examples of the electromagnetic wave loss material include a magnetic material and a conductive material. Examples of the conductive material include carbon particles, carbon fibers, metal particles, and hollow particles.

[0030] Examples of carbon particles include acetylene black, furnace black, channel black, ketjen black, oil furnace carbon, etc. Among these, ketjen black and carbon particles having conductivity equal to or higher than that of ketjen black are preferred, as they can provide the effect of controlling the dielectric constant with the addition of a small amount.

[0031] Examples of carbon fibers include pitch-based carbon fibers and PAN-based carbon fibers. One type of carbon fiber may be used alone, or two or more types may be used in combination. The average length of the carbon fibers is preferably 100 μm to 4000 μm. Within this range, high absorption properties can be obtained with a small amount of carbon fiber. The average length of the carbon fibers may be 150 μm or more, or may be 200 μm or more. Here, the average length refers to the average value of the lengths of 25 randomly selected carbon fibers measured with a scanning electron microscope (SEM). The average length refers to the average length of the carbon fibers (raw material) before ink preparation. It is preferable that the average length of the carbon fibers in the ink or radio wave absorber also be within the above range.

[0032] The metal particles are not particularly limited as long as they are particles made of a conductive metal. Iron is preferred as the metal. Examples of iron powder particles include spherical iron powder particles, flat iron powder particles, and soft magnetic iron alloy particles.

[0033] Examples of hollow particles include ceramic balloons, glass balloons, and shirasu balloons. In one embodiment, the average diameter (d50: median diameter) of the hollow particles is 1 / 10 or more and 1 / 2 or less, or 1 / 3 or less, of the average length described for carbon fiber. In one embodiment, the average diameter (d50: median diameter) of the hollow particles is 1 / 10 to 1 / 2 or 1 / 10 to 1 / 3 of the average length described for carbon fiber. The average diameter of the hollow particles is a value based on JIS Z 8819-1:1999.

[0034] In one embodiment, the filler contained in the first ink includes one or more types selected from the group consisting of carbon particles and carbon fibers. In one embodiment, the filler contained in the first ink includes only carbon particles. In one embodiment, the filler contained in the first ink includes only carbon fibers. In one embodiment, the filler contained in the first ink includes carbon particles and carbon fibers. In one embodiment, the filler contained in the second ink includes one or more types selected from the group consisting of carbon particles and carbon fibers. In one embodiment, the filler contained in the second ink includes only carbon particles. In one embodiment, the filler contained in the second ink includes only carbon fibers. In one embodiment, the filler contained in the second ink includes carbon particles and carbon fibers. When carbon particles and carbon fibers are used in combination in each ink, the mass ratio of the carbon particles to the carbon fibers (carbon particles:carbon fibers) is not particularly limited, and may be, for example, 1:99 to 99:1 or 10:90 to 90:10.

[0035] (Other Components) The first ink may contain components other than the resin and solvent as the main component, as long as the problem can be solved. The second ink may contain components other than the "component capable of curing the resin contained in the first ink" and the solvent as a curing agent, as long as the problem can be solved. The other components may include known resin additives and unavoidable impurities. Known resin additives include stabilizers against heat, light, ultraviolet rays, etc., lubricants, nucleating agents, plasticizers, antistatic agents, release agents, flame retardants, softeners, dispersants, antioxidants, colorants, etc. The total content of other components (or the total content of the known resin additives) in 100% by mass of the first ink may be 30% by mass or less, 20% by mass or less, 10% by mass or less, 8% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less. Furthermore, based on 100% by mass of the base agent of the first ink, the total content of other components (or the total content of the known resin additives) may be 40% by mass or less, 30% by mass or less, or 20% by mass or less. Based on 100% by mass of the second ink, the total content of other components (or the total content of the known resin additives) may be 10% by mass or less, 8% by mass or less, 5% by mass or less, 3% by mass or less, 2% by mass or less, 1% by mass or less, 0.8% by mass or less, 0.5% by mass or less, 0.3% by mass or less, or 0.1% by mass or less. Based on 100% by mass of the curing agent of the second ink, the total content of other components (or the total content of the known resin additives) may be 30% by mass or less, 20% by mass or less, or 10% by mass or less.

[0036] (Method of manufacturing ink set) The method of manufacturing the ink set is not particularly limited. In one embodiment, when the first ink contains a filler, the method of manufacturing the ink set includes mixing the base agent and the filler. In one embodiment, when the second ink contains a filler, the method of manufacturing the ink set includes mixing the curing agent and the filler. The method of mixing the base agent and the filler, and the method of mixing the curing agent and the filler are not particularly limited, and a mixer, for example, is suitably used. Examples of mixers include a rotation-revolution mixer, a disperser mixer, and a planetary mixer.

[0037] (Form of Ink Set) The form of the ink set is not particularly limited, as long as the first ink and the second ink are provided as separate entities. In one embodiment, the first ink is contained in a container, preferably a container that can seal the contents (first ink) (e.g., a container with a lid). In one embodiment, the second ink is contained in a container, preferably a container that can seal the contents (second ink) (e.g., a container with a lid).

[0038] In one embodiment, the ink set is provided as a set consisting of a first container containing a first ink and a second container containing a second ink. In embodiment α, the amount of the first ink in the first container and the amount of the second ink in the second container preferably satisfy at least one of the above-mentioned conditions 0≦B / (A+B)≦0.75 and A+B≦20% by mass, and preferably both. In this case, the ink set may further include a display urging the user to mix the entire amount of the first ink in the first container with the entire amount of the second ink in the second container before use. Alternatively, if the amounts of the first ink in the first container and the second ink in the second container are set arbitrarily, the inks may be dispensed from the respective containers so as to satisfy at least one of the above-mentioned conditions 0≦B / (A+B)≦0.75 and A+B≦20% by mass, and preferably both. The first ink and the second ink thus dispensed (the first ink and the second ink to be mixed at the time of use) also constitute the ink set according to this aspect (naturally, the explanation given for the ink set according to this aspect also applies to the dispensed first ink and the second ink). In this case, the ink set may further include an indication for urging the user to mix a predetermined amount of the first ink in the first container with a predetermined amount of the second ink in the second container before use. Here, it is preferable that the "predetermined amount" of each ink is set so as to satisfy at least one, and preferably both, of the above-mentioned conditions 0≦B / (A+B)≦0.75 and A+B≦20% by mass. In this way, for example, by a manufacturer or the like instructing (displaying) the blending ratio (or blending amounts) of the first ink and the second ink to the user, the user can easily manufacture a radio wave absorber having the intended performance (performance set by the manufacturer or the like). In the above explanation, the form of the indication is not particularly limited, and it may be displayed as a printed matter or may be displayed on the user's terminal via the Internet or the like. In one embodiment, a first container containing the first ink and a second container containing the second ink are housed in a single package. In the above description, the material of the containers is not particularly limited, and examples thereof include resin, glass, etc.The material of the packaging body is not particularly limited, and examples thereof include resin, paper (including cardboard, etc.), and the like.

[0039] The ink set of this embodiment is suitable for long-term storage and may be provided to users via transportation by vehicle, aircraft, or the like. In one embodiment, when the first ink contains a filler, one or more days, three or more days, seven or more days, or thirty or more days have passed since the base resin and the filler were mixed. The upper limit of the elapsed time is not particularly limited, and may be, for example, five years or less, three years or less, or one year or less. In one embodiment, when the first ink contains a filler, one to five years, three to five years, seven days to three years, or 30 days to one year have passed since the base resin and the filler were mixed. In one embodiment, when the second ink contains a filler, one to five days, three to five years, seven days to three years, or 30 days to one year have passed since the curing agent and the filler were mixed. The upper limit of the elapsed time is not particularly limited, and may be, for example, five years or less, three years or less, or one year or less. In one embodiment, when the second ink contains a filler, 1 day to 5 years, 3 days to 5 years, 7 days to 3 years, or 30 days to 1 year have passed since the curing agent and the filler were mixed, where 1 year is defined as 365 days.

[0040] 2. Mixture for Forming a Wave Absorber A mixture for forming a wave absorber according to one embodiment of the present invention (hereinafter also simply referred to as "mixture") is a mixture of the first ink and the second ink of the ink set for forming a wave absorber according to one embodiment of the present invention. A wave absorber can be formed by curing the mixture of this embodiment. According to this embodiment, since the ink set has excellent long-term storage stability, a user can prepare a mixture when needed, for example, using a stocked ink set, and can easily produce a wave absorber. Note that in the method for producing the mixture, the method for mixing the first ink and the second ink is not particularly limited, and a mixer, for example, is suitably used. Examples of mixers include a rotation-revolution mixer, a disperser mixer, and a planetary mixer.

[0041] 3. Method for Producing a Wave Absorber A method for producing a wave absorber according to one aspect of the present invention includes mixing the first ink and the second ink of the wave absorber-forming ink set according to one aspect of the present invention. In other words, the method for producing a wave absorber according to this aspect includes mixing the first ink and the second ink of the wave absorber-forming ink set, which includes the first ink containing a base agent and the second ink containing a curing agent, and at least one of the first ink and the second ink contains a filler. Note that in this aspect, the explanations given for the wave absorber-forming ink set according to one aspect of the present invention and the wave absorber-forming mixture according to one aspect of the present invention are incorporated by reference with respect to the first ink, the second ink, and their mixture. A wave absorber can be formed by curing the mixture (the mixture of the first ink and the second ink) obtained by this aspect. According to this aspect, the ink set has excellent long-term storage stability, so that a user can easily produce a wave absorber when needed, for example, by using a stocked ink set.

[0042] In one embodiment, a method for producing a radio wave absorber includes mixing the first ink and the second ink so as to satisfy the condition 0≦B / (A+B)≦0.75, where the mass of the filler contained in the first ink is A% by mass and the mass of the filler contained in the second ink is B% by mass, with the total mass of the first ink and the second ink being 100% by mass. In one embodiment, a method for producing a radio wave absorber includes mixing the first ink and the second ink so as to satisfy the condition A+B≦20% by mass, where the mass of the filler contained in the first ink is A% by mass and the mass of the filler contained in the second ink is B% by mass, with the total mass of the first ink and the second ink being 100% by mass. In one embodiment, a method for producing a radio wave absorber includes mixing the first ink and the second ink so as to satisfy both the condition 0≦B / (A+B)≦0.75 and the condition A+B≦20% by mass, where the total mass of the first ink and the second ink is 100% by mass, and the mass of the filler contained in the first ink is A% by mass and the mass of the filler contained in the second ink is B% by mass.

[0043] An example of a method for producing a radio wave absorber is a method in which the above-mentioned mixture (usually a mixed liquid) is formed into a film (by casting, by applicator, or the like) to a desired thickness, and then the film is cured. If the mixture contains bubbles, the mixture may be left to stand to degas. Alternatively, the mixture may be heated during curing.

[0044] In one embodiment, the film thickness standard deviation of the obtained radio wave absorber is 30 μm or less, 25 μm or less, 20 μm or less, 15 μm or less, 14 μm or less, 13 μm or less, 12 μm or less, 11 μm or less, or 10 μm or less. The lower limit is not particularly limited, and is, for example, 0.1 μm or more, 0.5 μm or more, 1 μm or more, 2 μm or more, or 3 μm or more. In one embodiment, the film thickness standard deviation of the obtained radio wave absorber is 0.1 to 30 μm, 0.1 to 25 μm, 0.1 to 20 μm, 0.1 to 15 μm, 0.5 to 14 μm, 1 to 13 μm, 2 to 12 μm, 2 to 11 μm, or 3 to 10 μm. A radio wave absorber having a film thickness standard deviation of 15 μm or less is suitable as a radio wave absorbing and shielding member, for example, in various communication fields. Furthermore, a radio wave absorber having a film thickness standard deviation of 10 μm or less is suitable as a radio wave absorbing and shielding member used in, for example, millimeter wave radar devices used in ships, aircraft, vehicles, etc., and electric and electronic devices, etc. Of course, the uses of the radio wave absorber are not limited to these. The film thickness standard deviation of the radio wave absorber is a value measured by the method described in the examples.

[0045] 4. Wave absorber A wave absorber according to one aspect of the present invention is produced using the ink set for forming a wave absorber according to one aspect of the present invention or the mixture for forming a wave absorber according to one aspect of the present invention. Because the ink set has excellent long-term storage properties, the wave absorber of this aspect can be easily produced by a user whenever required, for example, by using an ink set that has been stocked.

[0046] In this aspect, the description given for the radio wave absorber obtained by the method for producing a radio wave absorber according to one aspect of the present invention is used as appropriate for the configuration of the radio wave absorber (such as the standard deviation of film thickness).

[0047] 5. Radio wave absorbing structure A radio wave absorbing structure according to one aspect of the present invention includes a radio wave absorber according to one aspect of the present invention and a radio wave reflector laminated on one surface of the radio wave absorber. The radio wave reflector is not particularly limited as long as it has the property of reflecting radio waves without transmitting them, such as a metal plate, metal foil, or metal film. A resin layer such as a general adhesive layer may be formed between the radio wave absorber and the radio wave reflector. The radio wave absorbing structure can be manufactured, for example, by a method of directly depositing a radio wave absorber on the radio wave reflector, or a method of attaching the radio wave reflector to the radio wave absorber.

[0048] In one embodiment, the radio wave absorber and the radio wave absorbing structure have high radio wave absorbing performance over the entire frequency range of 20 GHz to 110 GHz, specifically, the amount of radio wave absorption over the entire frequency range of 20 GHz to 110 GHz is 80% or more, 85% or more, or 90% or more.

[0049] Examples of the present invention will be described below, but the present invention is not limited to these examples.

[0050] The materials used in the examples are as follows. <Main component> Silicone resin (polydimethylsiloxane, manufactured by Dow-Toray Industries, Inc., Silpot 184 (registered trademark), viscosity at 25°C: 9500 cP) <Curing agent> Curing agent (184C) included in Silpot 184 (registered trademark), manufactured by Dow-Toray Industries, Inc. <Filler> Carbon particles (acetylene black, manufactured by Denka Co., Ltd., Denka Black (pressed 100%)) Carbon fiber (milled fiber, manufactured by Nippon Graphite Fiber Co., Ltd., XN-100-25M, average length 250 μm)

[0051] Example 1 1. Preparation of First Ink Silicone resin (main component) and carbon particles (filler) were mixed to obtain the first ink. Here, mixing was performed using a planetary centrifugal mixer (Thinky Corporation, Awatori Rentaro ARE-310) and stirring was performed at 2000 rpm for 2 minutes.

[0052] 2. Preparation of second ink The curing agent was used as it was as the second ink.

[0053] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a liquid mixture. Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. In Table 1, "A [mass %]" represents the mass of the filler contained in the first ink relative to the total mass of the first ink and the second ink (100 mass %). Furthermore, "B [mass %]" represents the mass of the filler contained in the second ink relative to the total mass of the first ink and the second ink (100 mass %). The resulting mixture was allowed to stand for 10 minutes to degas. The mixture was then poured into a 10 cm square aluminum container, which was then heated on a hot plate at 100°C for 40 minutes to cure the mixture. The cured product (cast film) was then peeled off from the aluminum container to obtain a wave absorber.

[0054] 4. Evaluation Method (1) Cured State The cured state of the radio wave absorber was evaluated in accordance with JIS K 5600-1: 1999. Specifically, when the center of the coated surface (surface) of the radio wave absorber was pinched firmly between the thumb and index finger, no indentation due to fingerprints was left on the coated surface, no movement of the coating film (radio wave absorber) was felt, and no scratches were left on the coated surface even when the center of the coated surface was rapidly and repeatedly rubbed with the fingertips (dry-hard), the state was evaluated as "S".

[0055] (2) Film-forming ability and film thickness standard deviation The film thickness (sample film thickness) of the radio wave absorber was measured at five measurement points using a general digital linear gauge, and the standard deviation (film thickness standard deviation) was calculated. Based on the value of this film thickness standard deviation, the film-forming ability was evaluated according to the following evaluation criteria: S: Less than 10 μm A: 10 μm or more and less than 15 μm B: 15 μm or more and less than 30 μm Note that S to B are practically preferable. Specifically, the smaller the film thickness standard deviation, the easier it is for the radio wave absorber to be given the intended amount of radio wave absorption. This is because a shift in the absorption center is suppressed.

[0056] The results are shown in Table 1.

[0057] Example 2 1. Preparation of First Ink Silicone resin (base material) and carbon particles (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0058] 2. Preparation of second ink The curing agent and carbon particles (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0059] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0060] Example 3 1. Preparation of First Ink Silicone resin (base material) and carbon particles (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0061] 2. Preparation of second ink The curing agent and carbon particles (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0062] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0063] Example 4 1. Preparation of First Ink Silicone resin (base), carbon particles (filler), and carbon fibers (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0064] 2. Preparation of second ink: The curing agent, carbon particles (filler), and carbon fibers (filler) were mixed to obtain the second ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0065] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0066] Example 5 1. Preparation of First Ink Silicone resin (base material) and carbon fiber (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0067] 2. Preparation of second ink The curing agent and carbon fiber (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0068] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0069] Example 6 1. Preparation of First Ink Silicone resin (base), carbon particles (filler), and carbon fibers (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0070] 2. Preparation of second ink: The curing agent, carbon particles (filler), and carbon fibers (filler) were mixed together to obtain the second ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0071] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0072] Example 7 1. Preparation of First Ink Silicone resin (base material) and carbon particles (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0073] 2. Preparation of second ink The curing agent and carbon particles (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0074] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0075] Example 8 1. Preparation of First Ink Silicone resin (base material) and carbon particles (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0076] 2. Preparation of second ink The curing agent and carbon particles (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0077] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0078] Example 9 1. Preparation of First Ink Silicone resin (base material) and carbon particles (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0079] 2. Preparation of second ink The curing agent and carbon particles (filler) were mixed to obtain the second ink. Here, the mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0080] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0081] Example 10 1. Preparation of First Ink Silicone resin (base), carbon particles (filler), and carbon fibers (filler) were mixed to obtain a first ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0082] 2. Preparation of second ink: The curing agent, carbon particles (filler), and carbon fibers (filler) were mixed together to obtain the second ink. The mixture was stirred at 2000 rpm for 2 minutes using a planetary mixer.

[0083] 3. Formation of Wave Absorber The first ink and the second ink were mixed under the conditions shown in Table 1 to obtain a mixture (liquid). Here, a planetary centrifugal mixer was used for mixing, and the mixture was stirred at 2000 rpm for 2 minutes. As in Example 1, the obtained mixture was degassed and cured to obtain a wave absorber. The wave absorber was evaluated in the same manner as in Example 1.

[0084] The results are shown in Table 1.

[0085]

[0086] In all of the examples, the filler was contained in at least one of the first ink and the second ink constituting the ink set, resulting in excellent long-term storage stability, ease of handling, and the wave absorber could be easily prepared without weighing the filler itself. Furthermore, by satisfying the condition 0≦B / (A+B)≦0.75, and more preferably 0≦B / (A+B)≦0.70, it was found that the film-forming properties when forming the wave absorber could be improved and the standard deviation of the wave absorber's film thickness could be reduced. Furthermore, by satisfying the condition A+B≦20% by mass, it was found that the film-forming properties when forming the wave absorber could be improved, the standard deviation of the wave absorber's film thickness could be reduced, and the cured state could also be improved. In these examples, good results were confirmed for A in the range of 4% by mass or more and 7% by mass or less. Furthermore, good results were confirmed for B in the range of 0% by mass or more and 12% by mass or less. Furthermore, the amounts of filler contained in the first ink and the second ink could be adjusted so that the difference in viscosity between the first ink and the second ink was small, preferably so that the viscosities were equivalent. Furthermore, such adjustment could be performed within a range that satisfied at least one of the above-mentioned conditions of 0≦B / (A+B)≦0.75 and A+B≦20 mass %, thereby improving the mixability of the first ink and the second ink and further reducing the standard deviation of the film thickness of the obtained wave absorber.

[0087] The radio wave absorber of the present invention can be used as a member that absorbs radio waves in the millimeter wave region in vehicles, civil engineering structures, buildings, port facilities, ship facilities, bridges, power facilities, communication facilities, mechanical facilities, etc. Specifically, it is suitable as a radio wave absorbing and shielding member used in millimeter wave radar devices, electric and electronic devices, etc. used in ships, aircraft, vehicles, etc. Furthermore, it is suitable as a member that absorbs and shields unwanted radio waves in transportation infrastructure environments such as road guardrails, tunnel inner walls, and smart cities.

[0088] Although several embodiments and / or examples of the present invention have been described in detail above, those skilled in the art will readily be able to make numerous modifications to these exemplary embodiments and / or examples without substantially departing from the novel teachings and advantages of the present invention. Accordingly, these numerous modifications are within the scope of the present invention. The contents of all documents cited in this specification and of the applications from which this application claims priority under the Paris Convention are incorporated by reference in their entirety.

Claims

1. An ink set for forming a radio wave absorber, comprising: a first ink containing a base agent; and a second ink containing a curing agent, wherein at least one of the first ink and the second ink contains a filler.

2. The ink set for forming a radio wave absorber according to claim 1, wherein the filler is contained in only one of the first ink and the second ink.

3. The ink set for forming a radio wave absorber according to claim 1 or 2, wherein the filler is contained only in the first ink.

4. The ink set for forming a radio wave absorber according to claim 1, wherein the filler is contained in both the first ink and the second ink.

5. An ink set for forming a radio wave absorber according to any one of claims 1 to 4, wherein, when the total mass of the first ink and the second ink is 100% by mass, the mass of the filler contained in the first ink is A% by mass, and the mass of the filler contained in the second ink is B% by mass, the condition 0≦B / (A+B)≦0.75 is satisfied.

6. An ink set for forming a radio wave absorber according to any one of claims 1 to 5, wherein, when the total mass of the first ink and the second ink is 100% by mass, the mass of the filler contained in the first ink is A% by mass, and the mass of the filler contained in the second ink is B% by mass, the condition A + B ≦ 20% by mass is satisfied.

7. An ink set for forming a radio wave absorber according to any one of claims 1 to 6, wherein the mass of the filler contained in said first ink is 0 to 20 mass % with respect to 100 mass % of the total mass of said first ink and said second ink.

8. An ink set for forming a radio wave absorber according to any one of claims 1 to 7, wherein the mass of the filler contained in said second ink is 0 to 20 mass % with respect to 100 mass % of the total mass of said first ink and said second ink.

9. The ink set for forming a radio wave absorber according to any one of claims 1 to 8, wherein the mass of the filler is 0 to 25 mass % relative to 100 mass % of the mass of the first ink.

10. An ink set for forming a radio wave absorber according to any one of claims 1 to 9, wherein the mass of the filler is 0 to 70 mass % relative to 100 mass % of the mass of the second ink.

11. The ink set for forming a radio wave absorber according to any one of claims 1 to 10, wherein the main agent contains polydimethylsiloxane.

12. The ink set for forming a radio wave absorber according to any one of claims 1 to 11, wherein the filler comprises at least one type selected from the group consisting of carbon particles and carbon fibers.

13. The ink set for forming a radio wave absorber according to any one of claims 1 to 12, wherein the filler contains carbon particles and carbon fibers.

14. The ink set for forming a radio wave absorber according to any one of claims 1 to 13, wherein the viscosity of the base agent at 25°C is 10,000 cP or less.

15. A mixture for forming a radio wave absorber, which is a mixture of the first ink and the second ink of the ink set for forming a radio wave absorber according to any one of claims 1 to 14.

16. A method for producing a radio wave absorber, comprising mixing the first ink and the second ink of the ink set for forming a radio wave absorber according to any one of claims 1 to 14.

17. The method for producing a radio wave absorber according to claim 16, wherein the standard deviation of the film thickness of the obtained radio wave absorber is 15 μm or less.

18. A radio wave absorber produced using the ink set for forming a radio wave absorber according to any one of claims 1 to 14 or the mixture for forming a radio wave absorber according to claim 15.

19. The radio wave absorber according to claim 18, having a film thickness standard deviation of 15 μm or less.

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