JP6429139B2 - Wood-based magnetic molding material - Google Patents

Description

  In recent years, with the rapid spread of small information terminals such as smartphones, wireless LAN access points are prominent in public spaces, making it difficult to connect to the Internet due to radio wave congestion between the disturbed access points. .

  For such a problem, conventionally, by installing a building material having a radio wave absorption function using a ceramic material such as a calcium silicate plate or a mortar plate, radio wave propagation from the outside is prevented at a desired location, It has been proposed to construct an optimal wireless coverage area (Non-Patent Document 1).

  On the other hand, as a recent need for building materials, a gentle material feeling and natural feeling of wood materials are required. For this reason, there is a demand for the development of a radio wave absorber for interiors that has a wooden texture that does not feel strange with the surroundings. As an example of the development of a high-value-added wood material that can be used for such a radio wave absorber for interior use, magnetic wood in which magnetism is imparted to wood has been proposed (Patent Document 1). This is a composite material to which a GHz charging wave absorption effect due to magnetic loss is added in addition to the magnetic adsorption effect of the magnetic material.

Kenichi Kimura et al., IEICE Transactions B Vol.J88-B, No.6, p.1130-1138 (2005)

Japanese Patent No. 3135829

  However, it has been pointed out that problems with electromagnetic wave absorbers using magnetic wood include a decrease in magnetism and deterioration in radio wave absorption characteristics due to an increase in moisture content in a high humidity environment. It is not always easy to suppress the decrease in magnetism and the deterioration of radio wave absorption characteristics under humidity conditions.

  In addition, many conventional wave absorbers using magnetic wood target only a single frequency band, such as the 2.4 GHz band or the 5 GHz band used in wireless LAN.

  Therefore, the present invention provides a wood-based magnetic molding material having radio wave absorption characteristics for radio waves in a wide frequency band without lowering magnetism or radio wave absorption characteristics even under high humidity conditions. It is an issue.

  The present invention is characterized by the following in order to solve the above problems.

That is, the present invention is a wood-based magnetic molding material, which does not contain wood powder, and uses a molding material of a kneaded material containing resin, magnetic powder, a compatibilizing agent and a lubricant as an inner surface layer, on the surface of the inner surface layer. , wood flour, resin, magnetic powder are laminated as a molding material is a surface layer of the kneaded material containing the compatibilizer and lubricant, the kneading of the material before blending amount of the wood powder is molded in the surface layer 10% by mass to 60% by mass of the total weight of the product, 20% (vol%) to 60% (vol%) of the total volume of the resin, and the blended amount of the magnetic powder of the total weight of the kneaded product 5 mass% to 70 mass%, the addition amount of the compatibilizing agent is 0.5 mass% to 1.0 mass% with respect to the total weight of the kneaded product, and the addition amount of the lubricant is the total amount of the kneaded product. 0.5% by mass to 1.0% by mass with respect to the weight, the thickness after lamination is 4 to 15 mm, and 1 GHz to 8 G It has a radio wave absorption performance of 40 dB or more in the Hz band.
In the wood-based magnetic molding material of the present invention, it is preferably considered that the wood-based magnetic molding material has an EMC of 6% or less at a relative humidity of 90%.

  The compatibilizing agent is preferably maleic anhydride-modified polypropylene.

  The lubricant preferably contains low molecular weight polyethylene and calcium stearate.

  The resin is preferably either a recycled polypropylene resin or a phenol resin.

  According to the present invention, it is possible to provide a wood-based magnetic molding material having radio wave absorption characteristics for radio waves in a wide frequency band without deterioration of magnetism and radio wave absorption characteristics even under high humidity conditions. It becomes possible.

It is the graph which showed the result of the Brinell hardness test of the wood type magnetic molding material from which the compounding quantity of magnetic powder differs. It is the graph which showed the fracture coefficient (MOR) in the bending strength test of the wood type magnetic molding material from which the compounding quantity of magnetic powder differs. It is the graph which showed the bending Young's modulus (MOE) in the bending strength test of the wood type magnetic molding material from which the compounding quantity of magnetic powder differs. It is the graph which showed the proportional limit stress in the bending strength test of the wood type magnetic molding material from which the compounding quantity of magnetic powder differs. It is the graph which showed the parallel moisture content (EMC) in the moisture absorption-and-desorption process of the wood type magnetic molding material from which the compounding quantity of magnetic powder differs. This is a color map of maximum return loss for each layer thickness in a two-layer woody magnetic molding. 6 is a graph showing changes in frequency characteristics of return loss with respect to each layer thickness in a woody magnetic molding material having a two-layer structure.

  The woody magnetic molding material of the present invention is a molded body containing wood powder, resin, magnetic powder, a compatibilizing agent and a lubricant. In general, a molded body containing wood powder and resin is called wood plastic composites (WPC). WPC has advantages such as higher durability and weather resistance, less shrinkage due to drying, and higher moldability than wood.

  In the woody magnetic molding material of the present invention, in addition to wood powder and resin, magnetic powder, a compatibilizer and a lubricant are blended at a predetermined ratio, and kneaded with a stirrer or the like to prepare a kneaded product.

  The blending amount of the wood flour is preferably in the range of 10% by mass to 60% by mass of the total weight of the kneaded material of each material before molding. As the amount of wood powder increases, the wood texture of the resulting wood-based magnetic molding material improves, and it is lighter than conventional radio wave absorbers, but exhibits sufficient radio wave absorption capability. Is possible.

  Examples of the wood flour include those derived from wood such as wig, spruce, lawan and the like. These wood flours can be used alone or in combination of two or more. Selection of wood powder can be suitably selected according to the construction place etc. of a wood type magnetic molding material.

  The blending amount of the magnetic powder is preferably within the range of 5% by mass to 70% by mass of the total weight of the kneaded material of each material before molding.

  Examples of the magnetic powder include Sendust, nickel, pure iron, molybdenum permalloy, ferrite, and Mn—Zn ferrite. These magnetic powders can be used alone or in combination of two or more. The selection of the magnetic powder can take into account the desired magnetism and radio wave absorption characteristics. In particular, it is preferable to use Mn—Zn ferrite. The magnetic powder may be obtained by subjecting the powder surface to an antioxidant treatment.

  The addition amount of the compatibilizer is preferably in the range of 0.5% by mass to 1.0% by mass with respect to the total weight of the kneaded material of each material before molding.

  Examples of the compatibilizer include styrene butadiene rubber, maleic anhydride-modified polyolefin, maleic anhydride-modified polypropylene, and the like. These compatibilizers can be used alone or in combination of two or more. In particular, it is preferable to use maleic anhydride-modified polypropylene.

  The addition amount of the lubricant is preferably in the range of 0.5% by mass to 1.0% by mass with respect to the total weight of the kneaded material of each material before molding.

  As the lubricant, for example, it is preferable to include low molecular weight polyethylene and calcium stearate. By adding a lubricant, the dispersibility and fluidity of the magnetic powder in the kneaded material of each material are improved, and the radio wave absorption ability of the obtained wood-based magnetic molding material can be improved.

  The blending amount of the resin is preferably in the range of 20% by mass to 60% by mass of the total volume of the kneaded material of each material before molding.

  The type of resin is not particularly limited as long as it is a liquid thermoplastic resin. Examples thereof include isocyanate resins composed of MDI (diphenylmethane diisocyanate), TDI (tolylene diisocyanate), MDI prepolymer, TDI prepolymer, and the like. Also, polypropylene resin, urea resin, melamine resin, urea-melamine cocondensation resin, phenol resin, resorcinol resin, epoxy resin, urethane resin, furfural resin and the like are exemplified. In particular, either a recycled polypropylene resin or a phenol resin is preferable. These resins can be used alone or in combination of two or more. The selection of the resin can take into account the water resistance of the wood-based magnetic molding material, the amount of formaldehyde that causes sick house syndrome, and the like. Moreover, a content, a sizing agent, etc. can be added to resin as needed. By kneading such a resin with a wood-based magnetic molding material, the strength of the wood-based magnetic molding material is improved, and through the improvement of water resistance, the magnetism and radio wave absorption ability are reduced even under high humidity conditions. Can be suppressed.

  These materials are blended at a predetermined ratio and kneaded with a stirrer or the like to prepare a kneaded product.

  The kneading of the wood powder, resin, magnetic powder, compatibilizer and lubricant is preferably performed while heating in the range of 100 ° C to 250 ° C. The kneading time is preferably in the range of 1 minute to 30 minutes. As a kneading method, a commercially available kneader or stirring device can be appropriately selected. In the examples described later, a lab plast mill is used.

  When producing a wooden magnetic molding material, a kneaded product of each material is poured into a mold or the like of a desired shape, and hot-pressed to cure the resin. In molding by hot pressing, for example, a continuous press device that conveys the laminate while applying pressure to the gap between a pair of heated steel belts, or a multi-stage press that presses the kneaded material between a plurality of heated hot plates A device or the like can be used. The molding conditions are not particularly limited, and examples thereof include a molding temperature range of 80 ° C. to 220 ° C. and a molding pressure of 0.5 MPa to 4 MPa. The molding time can be appropriately set in consideration of the plate thickness, molding temperature, and the like.

  Examples of the plate thickness of the wood-based magnetic molding material after curing include a range of 4 mm to 15 mm.

  The wood-based magnetic forming material can be formed by laminating two or more layers of wood-based magnetic forming materials having different plate thicknesses and magnetic powder contents.

  In the wood-based magnetic molding material of the present invention, the wood layer is preferably made of a wood-based magnetic molding material having a high content of wood powder, because the objective is to achieve both wood texture and radio wave absorption capability. It is preferable to use a wood-based magnetic molding material having a high content of magnetic powder.

  When producing a wood-based magnetic molding material having a multilayer structure of two or more layers, a kneaded product having different magnetic powder contents is laminated in two layers in the order of the kneaded product for the inner surface layer and the kneaded product for the surface layer. Then, the laminate is hot pressed to cure the resin agent. The conditions for the hot pressing can be appropriately set from the same temperature and pressure conditions as those for the wood-based magnetic molding material having a single layer structure. In addition, a non-woody magnetic body such as a resin molded body not containing wood powder may be used for the inner surface layer.

Examples of the thickness of the wood-based magnetic molded material after lamination include a range of 4 mm to 15 mm. In particular, the present invention requires a thickness of 30 mm in order for a radio wave absorber using a gypsum spacer, which is a conventional product, to exhibit radio wave absorptivity in the 2.4 GHz band. Demonstrate. For this reason, the woody magnetic molding material of the present invention can prevent the living space from becoming narrow when it is constructed as an interior material. Further, the laminated wood-based magnetic molding material can have a radio wave absorption performance of 40 dB or more within a 1 GHz to 8 GHz band.

  Hereinafter, examples will be shown and described in more detail.

  Of course, the present invention is not limited to the following examples.

<Manufacture of wood-based magnetic molding materials>
Wood powder, recycled polypropylene, and Mn—Zn ferrite magnetic powder (diameter: 45 to 75 μm) are mixed at a volume ratio shown in Table 1, and further a compatibilizer (0.5 mass% to 1.0 mass%), pigment (0 0.5 mass%) and a lubricant (0.5 mass%) were added, and 300 g of each of the three types of compounds was prepared by kneading for 5 minutes at a kneading temperature of 180 ° C. using a lab plast mill (manufactured by Toyo Seiki). . M0 contains 81 vol% (47.52 mass%) of wood powder, 19 vol% (44.45 mass%) of recycled polypropylene, and does not contain magnetic powder. M2 contains 76 vol% (37.44 mass%) of wood powder, 22 vol% (44.33 mass%) of recycled polypropylene, and 2 vol% (9.85 mass%) of magnetic powder. M5 contains 64 vol% (23.65 mass%) of wood powder, 30 vol% (44.33 mass%) of recycled polypropylene, and 5 vol% (23.65 mass%) of magnetic powder. These were hot-pressed to a thickness of 5 mm to form a flat plate type sample. A specimen cut out from a flat plate sample with a width of 20 mm and a length of 60 mm or more was used as a test piece for evaluating mechanical strength characteristics.

<Evaluation of mechanical strength characteristics>
As the mechanical strength characteristics of each sample, a surface hardness test and a bending strength test were performed. As a surface hardness test, a Brinell hardness test using a metal ball having an indenter diameter of 10 mm was performed. At that time, the press-fit depth was fixed to 1 / π (= 0.32) mm for each test piece, and the Brinell hardness was calculated from the load at that time. FIG. 1 shows the Brinell hardness of each sample. In the figure, error bars indicate variations when 9 points are measured for each test piece. It was recognized that the surface hardness became harder as the magnetic powder ratio was higher.

Next, the result of a bending strength test is shown. FIG. 2 shows the failure coefficient (MOR) of each sample. The MOR of the wood-based magnetic molding materials (M2, M5) was within ± 10% of M0 not containing magnetic powder, and no significant difference was observed. That is, the influence of the reduction of the wood powder ratio and the mixing of the magnetic powder did not appear in the MOR. 3 and 4 show the bending Young's modulus (MOE) and proportional limit stress. It became clear that if wood powder is reduced or not mixed, rigidity increases and deformation is difficult, but acceptable stress is slightly reduced.
<Measurement of Equilibrium moisture content (EMC) in moisture absorption / desorption process>
Using the cedar chip as a control, each sample was subjected to EMC measurement. The air-dried sample after production was crushed to about a grain of rice and about 3 g was put in a weighing bottle as one test body, and 6 test bodies were prepared for each sample. These were distributed to six desiccators containing saturated salts that were conditioned to 85, 75, 62, 53, 43, and 33% relative humidity for humidity control. The desiccator was installed at a constant temperature of 20 ° C. In order to dehumidify all the specimens from 95% relative humidity to each humidity, the equilibrium weight was measured after conditioning for about 4 weeks. Further, all the test specimens were completely dried at 105 ° C., and the humidity during the moisture absorption process was calculated by adjusting the relative humidity of the above six conditions again for about 4 weeks.

The measurement result of EMC in the moisture absorption / desorption process is shown in FIG. As with cedar chips, adsorption / desorption hysteresis was also observed in the wood-based magnetic molding material. Here, in the wood-based magnetic molding material, the increase in the amount of moisture sorption when moving from the middle humidity range to the high humidity range (approximately 80% RH or more) was smaller than that of the cedar chip. The reason for this is considered to have received a thermal history of about 180 ° C. during the production of the wood-based magnetic molding material, which caused a decrease in hygroscopicity. Further, when the ratio of the equilibrium sorption amount (average value in both adsorption and desorption processes) to the cedar chip was determined, both M0 and M2 were about 34%, and M5 was 18%. This ratio is a slightly lower value when viewed from the compound law in consideration of the wood flour content, and it is considered that the influence of the heat history was applied. With this effect as well, even in M0, which has the highest EMC, a result was obtained in which the EMC remained at 6% at 90% relative humidity. This is about half the water content of ceramic materials such as mortar, which is a conventional product, and it is expected that the radio wave absorption characteristics do not change even under high humidity conditions.
<Evaluation of radio wave absorption characteristics>
The radio wave absorption characteristics when the two-layer structure was used were tested. Here, M5 having a wood texture is used as a surface layer, the lower layer does not contain wood flour, recycled resin is 60 vol% (31.58 mass%), and magnetic powder is 40 vol% (62.46 mass%) as a resin. The structure which plays a role as a radio wave absorption layer by M40 contained was examined. The return loss RL of the magnetic material is obtained as RL = −20 log ₁₀ Γ (dB) using the reflection coefficient Γ calculated from the input impedance of the radio wave absorber. FIG. 6 shows a color map of the maximum return loss RL _MAX with respect to the layer 1 thickness d ₁ and the layer 2 thickness d ₂ . In the figure, contour lines with RL _MAX of 10, 20, and 30 dB are also shown by solid lines. In the figure, when attention is focused on a region where the sum of d ₁ and d ₂ is about 10 mm or less, it can be seen that there is a region in which RL _MAX exceeds 40 dB in a semicircular arc shape. This means that the film thickness is matched and almost non-reflective (Γ≈0) by combination of appropriate film thicknesses of both layers. Here, as shown in FIG. 7, FIG. 7 shows the frequency characteristics of the return loss for the region 2 that satisfies the above-described non-reflection. In the case of the two-layer structure of M5 and M40, it became clear that the matching frequency can be controlled from 1.7 to 8 GHz by adjusting the thickness of each layer. This frequency range is a range including 2.45 GHz band and 5 GHz band which are wireless LAN standards. For this reason, the kneading type magnetic WPC is effective as an absorber material for radio waves for high-speed communication such as wireless LANs, etc. by using a two-layer structure that has a wood texture on the surface layer and mainly absorbs radio waves in the inner layer. It became clear that.

Claims (5)

The molding material of kneaded material containing no wood powder, resin, magnetic powder, compatibilizer and lubricant is used as the inner surface layer, and wood powder, resin, magnetic powder, compatibilizer and lubricant are applied to the surface of this inner surface layer. The molded material of the kneaded material to be contained is laminated as a surface layer, and the amount of the wood flour in the surface layer is 10% by mass to 60% by mass of the total weight of the kneaded material of each material before molding, the resin Is 20% (vol%) to 60% (vol%) of the total volume, the blending amount of the magnetic powder is 5% to 70% by weight of the total weight of the kneaded product, and the amount of the compatibilizer is added. Is 0.5% by mass to 1.0% by mass with respect to the total weight of the kneaded product, and the addition amount of the lubricant is 0.5% by mass to 1.0% by mass with respect to the total weight of the kneaded product. , and the a plate thickness after lamination 4 to 15 mm, having a 40 dB or more electromagnetic absorption performance in 1GHz~8GHz band Wooden magnetic molding material characterized by.   The wood-based magnetic molding material according to claim 1, wherein the wood-based magnetic molding material according to claim 1 has an EMC of 6% or less at a relative humidity of 90%.   The wood-based magnetic molding material according to claim 1 or 2, wherein the compatibilizing material is maleic anhydride knitted polypropylene.   The woody magnetic molding material according to any one of claims 1 to 3, wherein the lubricant includes low molecular weight polyethylene and calcium stearate.   The woody magnetic molding material according to any one of claims 1 to 4, wherein the resin is a recycled polypropylene resin or a phenol resin.