JP5065768B2 - Manufacturing method of radio wave absorber - Google Patents

Description

  The present invention relates to a method of manufacturing a radio wave absorber in which a mixture of non-conductive particles and conductive particles is molded into a predetermined shape to obtain a radio wave absorber, and in particular, dispersion of non-conductive particles and conductive particles. It relates to measures to suppress defects.

For example, as described in Patent Document 1, as a method of manufacturing a radio wave absorber, non-conductive particles and conductive particles obtained by imparting conductivity to the non-conductive particles are uniformly mixed. It is known to form a mixture into a predetermined shape by a mold or the like.
Japanese Unexamined Patent Publication No. 4-56298 (page 2)

  However, in the above conventional case, even if uniform at the time of mixing, vibrations are applied after mixing or the dispersibility between the non-conductive particles and the conductive particles tends to decrease with filling into the mold, As a result, there is a problem that the radio wave absorption performance is adversely affected.

  The present invention has been made in view of such points, and its main purpose is to produce a radio wave absorber when a mixture of non-conductive particles and conductive particles is molded into a predetermined shape. An object of the present invention is to make it possible to suppress a decrease in dispersibility between conductive particles and conductive particles, and to avoid deterioration of radio wave absorption performance due to such a decrease in dispersibility.

In order to achieve the above object, in the present invention, the non-conductive particles and the conductive particles vary in particle size, and the average density difference between the non-conductive particles and the conductive particles in the average density of the non-conductive particles. By keeping the ratio within a certain range and taking an antistatic measure, the dispersibility of the non-conductive particles and the conductive particles is hardly lowered.

  Specifically, in the present invention, a non-conductive particle and a conductive particle are mixed, and a mixture of the non-conductive particle and the conductive particle is molded into a predetermined shape to obtain a radio wave absorber. The manufacturing method is assumed.

And as said nonelectroconductive particle and electroconductive particle, each particle size Dn and Dc are within the range of +/- 15 % of the average particle diameter Dna of the said nonelectroconductive particle (Dna * [100% -15%], respectively). proportion of ≦ Dn, Dc ≦ Dna × [100% + 15%]) der is, and the average density difference between the non-conductive average density Mna accounted nonconductive particles and conductive particles of the particles (Mna-Mca) Mdr (= {[Mna−Mca] / Mna} × 100%) is within a range of ± 20% (100% −20% ≦ Mdr ≦ 100% + 20%).

Instead of the non-conductive particles, in the range of ± 15% of the average particle diameter Dca of the conductive particles (Dca × [100% - 15%] ≦ Dn, Dc ≦ Dca × [100% + 15%]) You may make it use what is. Here, the conductive particles are those obtained by imparting conductivity to non-conductive particles . Specifically, a conductive layer is formed on the surface of particles having the same non-conductivity as the non-conductive particles .

Further, after the non-conductive particles and the conductive particles are mixed, before the mixture of the non-conductive particles and the conductive particles is formed into a predetermined shape, an antistatic agent is sprayed on the mixture.

Further, instead of the antistatic agent spraying or in combination with the antistatic agent spraying, the nonconductive particles and the conductive particles are mixed, and then a mixture of the nonconductive particles and the conductive particles. The mixture can be accommodated in a container having an antistatic layer on the inner wall until it is molded into a predetermined shape.

Further, as the non-conductive particles made of foamed particles having a non-conductive, and the average density Mna is ^{0.01~0.2mg / mm 3 (0.01mg / mm} 3 ≦ Mna ≦ 0.2mg / mm 3) while used as is, as the conductive particles, made of foam particles having conductivity, and an average density Mca is also ^{0.01~0.2mg / mm 3 (0.01mg / mm} 3 ≦ Mca ≦ 0.2mg / Mm ³ ) can be used, and as the non-conductive particles and the conductive particles, the average particle diameters Dna and Dca are in the range of 1 to 4 mm, respectively (1 mm ≦ Dna, Dca ≦ 4 mm), or Those within a range of 2 to 3 mm (2 mm ≦ Dna, Dca ≦ 3 mm) can also be used.

According to the present invention, when producing a radio wave absorber by molding a mixture of non-conductive particles and conductive particles into a predetermined shape, each particle size is as described above as the non-conductive particles and the conductive particles. range der of ± 15% of the average particle size of the non-conductive particles is, and the range rate is ± 20% of the average density difference between the non-conductive particles and conductive particles occupying in the average density of the non-conductive particles After the non-conductive particles and the conductive particles are mixed using the inner layer, the mixture is placed on the inner wall surface until the mixture of the non-conductive particles and the conductive particles is formed into a predetermined shape. After the non-conductive particles and the conductive particles are mixed, and before the mixture of the non-conductive particles and the conductive particles is formed into a predetermined shape, an antistatic agent is sprayed on the mixture. So that dispersion of non-conductive particles and conductive particles It is possible to suppress deterioration of, with, it is possible to avoid the deterioration of the radio wave absorption performance due to the reduction of such dispersible.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings.

  FIG. 1 is a block diagram showing a manufacturing process of the radio wave absorber in the present embodiment. FIG. 2 is a perspective view schematically showing a radio wave absorber obtained by the manufacturing process. This radio wave absorber is used as a radio wave absorber for an anechoic chamber, for example.

  This electromagnetic wave absorber is a mixture of white beads (non-conductive particles) that are non-conductive foam particles and black beads (conductive particles) that are conductive foam particles, and the mixture is put into a mold from a hopper. It is obtained by being supplied and molded into a predetermined shape by the mold.

  In step # 1 in the manufacturing process of the radio wave absorber, first, white beads are manufactured. In this case, the white beads as an intermediate material for obtaining the black beads and the white beads mixed with the black beads may be made of the same material or different materials. However, when both are fused by heating, it is generally preferable that they are made of the same material.

  Next, in step # 2, a process for imparting conductivity to the white beads (conductive process) is performed to obtain black beads. Specifically, a conductive liquid containing conductive powder is added to white beads, stirred, and dried to form a conductive layer made of conductive powder on the surface of the white beads. . In addition, as said electrically conductive liquid, what added the adhesive agent, the flame retardant, etc. may be added, and also it adds organic polymer latex to said electrically conductive layer, stirs, and dries it. Thus, a coating layer that prevents the conductive powder in the conductive layer from peeling off may be provided.

  In step # 3, the white beads obtained in step # 1 and the black beads obtained in step # 2 are mixed at a predetermined mixing ratio (for example, white bead weight: black bead weight = 1: 0.5). To do. At that time, the white beads and the black beads are sufficiently dispersed to a necessary extent.

  In step # 4, the above mixture is supplied from the hopper through the hose into the mold, heated with water vapor to fuse the white beads and black beads, and then cooled to form a predetermined shape.

  Through the above steps # 1 to # 4, for example, a radio wave absorber (see FIG. 2) in which a plurality of quadrangular pyramids are erected on the substrate is obtained. Note that the radio wave absorber is not limited to the one having a quadrangular pyramid shape standing upright, and one having another shape such as a cone or a truncated cone may be standing upright. However, depending on the required radio wave absorption characteristics, a flat plate shape may be used.

  In this embodiment, as the white beads, the particle diameter Dn [unit: mm] is within ± 15% of the average particle diameter Dna of the white beads (Dna × [100% −15%] ≦ Dn ≦ Dna × [100% + 15%]) was used so that the variation in the particle diameter Dn was reduced. The black beads also have a particle size Dc [unit: mm] within a range of ± 15% of the average particle size Dna of white beads (Dna × [100% −15%] ≦ Dc ≦ Dna × [100% + 15). %]).

Further, in the present embodiment, as white beads, the average density Mna [Unit: mg / mm ^3] is ^{0.01~0.2mg / mm 3 (0.01mg / mm} 3 ≦ Mna ≦ 0.2mg / mm 3) while used as is, as the black beads, so the use of an average density Mca is also ^{0.01~0.2mg / mm 3 (0.01mg / mm} 3 ≦ Mca ≦ 0.2mg / mm 3) I made it. At that time, the ratio Mdr (= {[Mna−Mca] / Mna} × 100%) of the average density difference (Mna−Mca) between the white beads and the black beads to the average density Mna of the white beads is ± 20%. (100% -20% ≦ Mdr ≦ 100% + 20%). That is, the degree of the average density difference (Mna−Mca) between the white beads and the black beads was made small.

  Further, in the present embodiment, as shown in FIG. 3, a container 10 in which an antistatic layer 30 made of, for example, a rubber material is provided on the inner wall surface of the container body 20 is used. The mixture with black beads was accommodated and supplied to the hopper.

  In addition, when supplying the mixture in the hopper into the mold, an antistatic agent (for example, those classified into surfactant type, silicone type, organoboron type) is added to the mixture immediately before the mold. The ones appropriately selected or those appropriately mixed) were supplied. The antistatic agent may be water.

  Here, for the white beads obtained in the first step and the black beads obtained in the second step, a plurality of types of white beads having different average particle diameters Dna and average densities Mna, respectively, and a conductive layer on the surface of each white bead A test in which a plurality of types of black beads having different average densities Mca are combined and their dispersibility is determined will be described. There were four combinations. In this test, black beads having a conductive layer formed on the surface of white beads were used.

  First, 100 white beads were taken out for each combination, and the particle diameter Dn and weight of each white bead were measured, and the average particle diameter Dna and average density Mna were calculated. Next, for the black beads obtained by subjecting the above white beads to charging, 100 black beads were taken out for each combination, and the average density Mca was calculated by measuring the particle diameter Dc and the weight of each black bead. .

  First, for each combination, the maximum value Dnmax and the minimum value Dnmin of the particle diameter Dn are extracted, and the ratio DmaxR (unit:%) of the maximum value Dnmax to the average particle diameter Dna and the ratio DminR [ Unit:%] was calculated by the following formulas 1) and 2), respectively.

DmaxR = [(maximum value Dnmax−average value Dna) / average value Dna] × 100 1)
DminR = [(minimum value Dnmin−average value Dna) / average value Dna] × 100 2.
In this test, the conductive layer of black beads has a film thickness on the order of several μm and the influence on the particle size is negligible. Therefore, with the particle size Dn of white beads, which is the previous stage of black beads, Therefore, the particle size Da of the black beads was replaced.

  Next, for each combination, the ratio MdR (unit:%) of the average density difference (Mna−Mca) between the white beads and the black beads in the average density Mna of the white beads was calculated by the following equation 3).

MdR = [(Mna−Mca) / Mna] × 100 3)
As a result, the maximum value Dnmax, the minimum value Dnmin, and the average particle diameter Dna of the particle size Dn of the white beads are Dnmax = 3.80 mm, Dnmin = 2.78 mm, and Dna = 3.23 mm in the case of the combination 1. In the case of the combination 2, Dnmax = 3.04 mm, Dnmin = 2.43 mm, and Dna = 2.72 mm. In the case of the combination 3, Dnmax = 3.00 mm, Dnmin = 1.33 mm, and Dna = 2.28 mm. In the case of the combination 4, Dnmax = 2.90 mm, Dnmin = 1.10 mm, Dna = It was 2.05 mm.

  The ratio DmaxR of the maximum value Dnmax to the average particle diameter Dna and the ratio DminR of the minimum value Dnmin are DmaxR = + 15% and DminR = -14% in the case of the combination 1, and in the case of the combination 2, DmaxR = + 12% and DminR = -11%. In the case of combination 3, DmaxR = + 32% and DminR = −42%, and in the case of combination 4, DmaxR = + 41% and DminR = −46%.

The average density Mna, Mca of the white beads and black beads and the ratio of the average density difference between the white beads and black beads in the average density Mna of white beads MdR [unit:%] (= {[Mca-Mna] / Mna} × 100), in the case of combination 1, Mna = 0.17 g / cm ³ , Mca = 0.19 g / cm ³ , MdR = 11.8%, and in the case of combination 2 the a ^{Mna = 0.035g / cm 3, Mca} = 0.042g / cm 3, MdR = 20%. In the case of the combination ^{3, Mna = 0.096g / cm 3,} Mca = 0.132g / cm 3, an MDR = 37.5%, in the case of combined 4, Mna = 0.123 g / cm ³ , Mca = 0.178 g / cm ³ , MdR = 44.7%.

  Next, for each combination, white beads and black beads are mixed in a beaker with a weight ratio of 1: 0.5 (white bead weight: black bead weight). Stir well and disperse so that the appearance is the same in the combination. Then, for each combination, shake the beaker by hand to give vibration for 1 minute. The distributed state is judged.

  The results of the above combinations 1 to 4 are shown together with each data in the following table. In addition, each evaluation is "◎ (the level at which the initial dispersibility is substantially maintained)", "○ (the level at which the initial dispersibility is reduced but there is no problem in performance)", "△" Although the dispersibility is considerably lowered, it can be put to practical use) and “× (the level at which the initial dispersibility is greatly reduced and cannot be used)”.

  As can be seen from the above table, the combination 2 was evaluated as “◎” and the combination 1 was also evaluated as “◯”, whereas the evaluations of the combinations 3 and 4 were both “x”. there were. From these, it can be seen that, in combination 1 and combination 2, the degree of variation in particle diameters Dn and Dc is both within ± 15% of average particle diameters Dna and Dca, and white occupies the average density of white beads. Although the average density difference ratio Md between the beads and the black beads is both ± 20%, the average particle diameters Dna and Dca of the white beads and the black beads are in the range of 2 to 3 mm in the case of the combination 2. On the other hand, in the case of the combination 1, it is considered that it is out of the range of 2 to 3 mm.

  On the other hand, in the combination 3 and the combination 4, the average particle diameters Dna and Dca of the white beads and the black beads are both in the range of 2 to 3 mm. In the combination 3, the white beads and the average density Mna of the white beads Although the ratio MdR of the average density difference (Mna-Mca) between the black beads is within the range of ± 40%, the degree of variation in the particle diameters Dn and Dc is in any case ±± of the average particle diameters Dna and Dca. It is considered that the evaluation was “x” because this point greatly deviated from the range of 15% and even out of the range of ± 40%.

  Therefore, according to the present embodiment, the white beads and the black beads obtained by imparting conductivity to the white beads are mixed, and the mixture of the white beads and the black beads is formed into a predetermined shape to form the radio wave absorber. In production, white beads and black beads having particle diameters Dn and Dc within the range of ± 15% of the average particle diameter Dna of white beads are used. A decrease in dispersibility between the black beads can be suppressed, and thus deterioration of radio wave absorption performance due to such a decrease in dispersibility can be avoided.

At that time, the average particle diameters Dna and Dca of the white beads and the black beads are kept within a range of 2 to 3 mm, and the ratio of the average density difference between the white beads and the black beads in the average density Mna of the white beads. While controlling MdR to within ± 20% and using an average density Mna and Mca of 0.01 to 0.2 mg / mm ³ , and further mixing white beads and black beads, the white beads In addition to using a container 10 having an antistatic layer 30 on the inner wall as the container 10 used for storing the black bead mixture until it is molded into a predetermined shape, the container 10 is transferred from the hopper to the mold. Since the antistatic agent is sprayed between them, it is possible to prevent a decrease in dispersibility due to the white beads and black beads being charged and attached to the cavity surface in the mold.

  In the above embodiment, the white beads and the black beads are those in which the ratio of the average density difference (Mna−Mca) between the white beads and the black beads to the average density Mna of the white beads is within a range of ± 20%. However, instead of the range of ± 20%, a range of ± 40% may be used.

  Further, in the above embodiment, as the white beads and the black beads, those having the particle diameters Dn and Dc within the range of ± 15% of the average particle diameter Dna of the white beads are used. In this case, the average particle diameter Dna of white beads may be within a range of ± 40%. Furthermore, instead of the average particle diameter Dna of white beads, ± 15% or ±± of the average particle diameter Dca of black beads may be used. What is in the range of 40% can also be used.

  In the above embodiment, the non-conductive particles and the conductive particles are each non-conductive foam particles (white beads) and those obtained by conducting a conductive treatment on the surface of the foam particles (black beads). In the present invention, in addition to such foamed particles, the present invention can also be applied to the case of using particles made of glass or resin.

FIG. 1 is a perspective view schematically showing a radio wave absorber according to an embodiment of the present invention. FIG. 2 is a block diagram showing a manufacturing process of the radio wave absorber. FIG. 3 is a cross-sectional view schematically showing the configuration of a container used to contain a mixture of white beads and black beads.

10 Container 30 Antistatic layer

Claims (6)

A method of manufacturing a radio wave absorber, in which non-conductive particles and conductive particles are mixed, and a mixture of the non-conductive particles and the conductive particles is molded into a predetermined shape to obtain a radio wave absorber,
As the conductive particles, those having a conductive layer formed on the surface of the same non-conductive particles as the non-conductive particles,
As the non-conductive particles and conductive particles, respectively, Ri any range der of ± 15% of one of the average particle size of each particle size is the non-conductive particles or conductive particles, and the non The ratio of the average density difference between the non-conductive particles and the conductive particles in the average density of the conductive particles is within a range of ± 20%,
After mixing the non-conductive particles and the conductive particles, the mixture is accommodated in a container having an antistatic layer on the inner wall until the mixture of the non-conductive particles and the conductive particles is formed into a predetermined shape. A method of manufacturing a radio wave absorber characterized by comprising: A method of manufacturing a radio wave absorber, in which non-conductive particles and conductive particles are mixed, and a mixture of the non-conductive particles and the conductive particles is molded into a predetermined shape to obtain a radio wave absorber,
As the conductive particles, those having a conductive layer formed on the surface of the same non-conductive particles as the non-conductive particles,
Each of the non-conductive particles and the conductive particles has a particle size within ± 15% of the average particle size of either the non-conductive particles or the conductive particles, and the non-conductive particles. The ratio of the average density difference between the non-conductive particles and the conductive particles in the average density of the conductive particles is within the range of ± 20%,
After mixing the non-conductive particles and the conductive particles, before forming the mixture of the non-conductive particles and the conductive particles into a predetermined shape, an antistatic agent is sprayed on the mixture. Manufacturing method of absorber. In the manufacturing method of the electromagnetic wave absorber according to claim 1 or 2 ,
As the non-conductive particles, those comprising non-conductive foamed particles and having an average density of 0.01 to 0.2 mg / mm ³ are used.
A method for producing a radio wave absorber, wherein the conductive particles are made of foamed particles having conductivity and have an average density of 0.01 to 0.2 mg / mm ³ . In the manufacturing method of the electromagnetic wave absorber of any one of Claims 1-3 ,
A method for producing a radio wave absorber, wherein the non-conductive particles and the conductive particles each have an average particle diameter in the range of 1 to 4 mm. In the manufacturing method of the electromagnetic wave absorber according to any one of claims 1 to 4 ,
Above for the non-conductive particles and conductive particles, respectively, the manufacturing method of the wave absorber having an average particle diameter which comprises using those in the range of 2 to 3 mm. In the manufacturing method of the electromagnetic wave absorber according to claim 2 ,
After mixing the non-conductive particles and the conductive particles, the mixture is accommodated in a container having an antistatic layer on the inner wall until the mixture of the non-conductive particles and the conductive particles is formed into a predetermined shape. A method of manufacturing a radio wave absorber characterized by comprising:

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