JPS59117005A - Electromagnetic shielding material - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a novel electromagnetic shielding material.

Recently, with the spread of various electronic devices, electromagnetic noise caused by these devices is becoming a serious social problem. For this reason, there has been an increasing need for electromagnetic shielding materials to prevent disturbances caused by such noise.

As this ←M electromagnetic shielding material, materials sprayed with metal on a suitable base material and materials coated with conductive paint are known, but these are expensive and have poor durability, so they are not practical. This cannot necessarily be said to be satisfactory. In order to overcome these problems, it has been proposed to mix plastics with conductive fillers such as metal fibers or metal powders, but if the amount of metal fillers that are effective for electromagnetic shielding is mixed, the moldability will be reduced. This results in a decrease in mechanical strength and limits the use of the material.

The present inventors have overcome the drawbacks of such conventional electromagnetic shielding materials, and have demonstrated excellent electromagnetic shielding effects.
As a result of intensive research to develop a material with high strength and good formability, we found that when a plastic contains a metal coated on the surface of an inorganic filler using a chemical plating method. We have discovered the unexpected fact that a material with excellent electromagnetic shielding properties can be obtained, and its strength is significantly increased, and based on this knowledge, we have developed the present invention.

That is, the present invention provides an electromagnetic shielding material made of plastic and an inorganic optical brightener having a metal film firmly adhered by chemical plating on its surface.

Unlike metal fibers and metal powder, the filler used in the present invention is a stable inorganic substance inside and has metal only on the surface, so it is chemically stable and when mixed into plastic, It has the advantage that high conductivity can be provided with a small metal content without impairing formability, and that a high reinforcing effect can be obtained by using a plate-like filler such as mica.

As the inorganic powder used as a substrate for the filler, inorganic substances conventionally used as extenders, colorants, and reinforcing agents for plastics, rubber, etc. can be used. Examples of such substances include, for example, muscovite mica,
In addition to platy mica minerals such as phlogopite, synthetic fluorine-based mica, potassium titanate whiskers, acicular minerals such as wollastonite, asbestos, and sepiolite, silica, alumina, glass flakes, glass fiber,
Examples include carbon fiber and silicon fiber, but plate-shaped mica minerals are particularly preferred from the viewpoint of reinforcing effect. In the present invention, the formation of a metal film on inorganic powder is carried out by chemical plating, so the inorganic powder used needs to be stable against chemical plating solutions. The shape of the inorganic powder is not limited, and can be in various shapes such as a plate, needles or fibers, and granules.

In the present invention, such inorganic powder is subjected to chemical plating treatment to form a metal film on its surface. In this case, various conventionally known chemical plating solutions may be employed as the chemical plating solution. I can do it. In addition, various metals can be mentioned as metals added to the plating solution to form a surface film on the inorganic powder, for example,
Ni, Co, Ag, Au, Cu, Pd, Pt
, Rh', Ru, Fe, etc.

The metal film formed on the surface of the inorganic powder may be made of a single metal or an alloy such as Ni-Co or N1-W.

N1--Fe, Co-W, Co-Fe, Ni-Cu
When forming an alloy film, a plurality of metal salts may be added to the plating solution as desired.

In order to form a strongly adherent metal film on inorganic powder according to the present invention, it is necessary to first perform a degreasing process and then perform a specific base treatment, similar to the conventional plating process. . The surface treatment in this case is performed to easily deposit the metal film layer on the inorganic powder, and depending on the type of film metal to be formed on the surface, (1) 1 to 30 g of stannous chloride; A method of immersion treatment using an aqueous solution containing /fl and hydrochloric acid 1 to 30 + n Q / Q, and then immersion treatment using an aqueous solution containing palladium chloride 0.1 to Ig / Q and hydrochloric acid 1 to 10 m Q / Q, ( 2) Palladium chloride 0.1~Ig/Q and hydrochloric acid 1~30mQ/
A method of immersion treatment using an aqueous solution containing Q, (3) palladium chloride 0.2-3 g/Q, stannous chloride 10-4
A method of immersion treatment using an aqueous solution containing 0 g/Q and hydrochloric acid ioo to 200 m Q/Q and then treatment with a 5 to 10% hydrochloric acid aqueous solution is adopted.

After the above-mentioned surface treatment is completed, the inorganic powder is subjected to chemical plating treatment. In this case, chemical plating treatment can be performed according to a conventionally known method, and generally, metal salts, reducing agents, and complexing agents are used. A plating solution containing agents, buffers, stabilizers, etc. is used. In this case, the reducing agent used is sodium hypophosphite, sodium borohydride, aminoborane, formalin, etc., and the complexing agent or buffer agent used is formic acid, acetic acid, succinic acid, citric acid, tartaric acid, malic acid, etc. , glycine, ethylenediamine, EDTA, 1-liethanolamine, etc. are employed.

Typical compositions of chemical plating solutions include, for example, metal! 1
0~200g/Q, next 'fi'J:/WL,N
O, 3-50g/Q.

For example, a pH buffer containing 5 to 300 g/Q of glycine may be added, and preferably 5 to 200 g/Q of glycine as an auxiliary additive to such a plating solution.
Q can be added. In addition, as other plating liquids, metal salts 10-200g/Q, carboxylates 10-200g/Q
100g/Q, alkali hydroxide 10-60g/ρ, alkali carbonate 5-50g/Ω, formalin 10-200m
It consists of Ω/Ω, and typical metals that can be plated include copper and silver.

It is preferable that the chemical plating treatment is usually carried out at a temperature of 20 to 95° C. while stirring, for example, air bubbling, so that a uniform film is formed on the powder surface. In this way, plating is continued until a metallization ratio of at least 90% by weight is finally obtained.

In the present invention, the inorganic powder having the metal film on the surface obtained as described above is applied to the plastic for 10 to 10 minutes.
It is added in a proportion of 70% by weight to form a desired electromagnetic shielding material.

The plastic used in the present invention may be either a thermoplastic plastic or a thermosetting plastic, such as polyethylene, polypropylene, polystyrene, polyvinyl chloride, polymethyl methacrylate, polyethylene terephthalate, polybutylene terephthalate, polycarbonate, polyacetal resin, and polyurethane resin. , nylon 6° ethylene-vinyl acetate copolymer, ethylene-acrylic acid copolymer, ABS resin, epoxy resin, unsaturated polyester resin, phenol resin, etc. are used.

The electromagnetic shielding material of the present invention can be applied in a conventionally used shape, and in order to form a molded article for manufacturing a product, a mixture of plastic and a filler can be formed by vacuum forming, extrusion molding, injection molding, etc. Molding.

Methods such as calendar molding and compression molding are used, and
To make a coating composition for film formation, fillers can be added to and mixed with a plastic emulsion or a plastic solvent solution.Furthermore, when used as a rubber composition, it can be added to the ordinary rubber composition. On the other hand, the above filler may be added.

The electromagnetic shielding material of the present invention has excellent electromagnetic shielding properties and high strength, and is particularly useful as equipment for various electronic devices, communication devices, medical devices, measuring instruments, and the like.

Next, the present invention will be explained in more detail with reference to Examples. The metallization rate of the filler in each example was defined as follows.

Reference Example Mica and glass flakes with an average particle size of 60 mesh were immersed in an acidic aqueous solution of palladium chloride in hydrochloric acid to perform a surface treatment. Next, this ground-treated mica powder was put into a plating solution having the following composition, and treated at a temperature of 60 to 90° C. for 10 to 30 minutes while air stirring was performed.

Plating solution composition: Nickel sulfate・・・・・・・・・・・・・・・3
0g/Q Sodium hypophosphite・・・・・・・・・・
10. / Q Sodium citrate・・・・・・・・・・・・
・・10g/QpH・・・・・・・・・・・・・・・・
...S...4 to 6 The obtained matted product was dried to obtain a product.

This product has 8 nickel films on its surface, and when the powder was tested for conductivity using a tester, it was found to have good conductivity.

Fillers having the combinations shown in Table 1 were obtained in the same manner as above by changing the types of inorganic powder and metal compounds in the plating solution.

Example 1 After kneading polypropylene with nickel-plated progopyte mica (average particle size: 60 mesh) using a Brabender plasto mill, the material was hot-pressed to a thickness of 2n+m, and the surface resistance and volume resistivity were measured. The results are shown in Table 2.

For comparison, this table also shows examples using fillers without metal coatings.

For test pieces Nos. 1 to 5 in Table 2, the volume fraction of mica in polypropylene is approximately 12 to 15% when the volume of the nickel film on the mica surface is ignored;
Nos. 6 to 7 are molding materials obtained by filling mica to a volume fraction of about 30%. Plating film (specific gravity:
As the thickness of 7.95) increases, the electrical resistance decreases exponentially. In compression molded test pieces, when filled with plate-like or fibrous fillers, anisotropy is observed in the volume resistivity. As seen in test piece No. 5, the effect of overcoloring by forming a nickel oxide film is produced, but the resistance value becomes large. However, as shown in Table 3 below, the electromagnetic shielding property was io, 5 dB, indicating an effect. Test piece N
o 4 was treated with γ-aminopropyltriethoxysilane to improve adhesion in polypropylene and molded with 0.51% retention on the surface, but it had slightly less resistance than test piece No. 3. becomes larger, which is consistent with the decrease in shielding performance shown in Table 3 below.

When a hydrophilic plastic is used as a matrix, there is generally no need for surface treatment and there is no need to worry about a decrease in conductivity. What is the specific gravity of Phlogopite mica? 80 to 2.90, and conductivity can be obtained just by coating the surface with nickel, so
The effectiveness was achieved using a molding material with a lower specific gravity than when filling with nickel metal foil.

Example 2 Conducted. Measurements were made using a rectangular waveguide for the 4 GHz band (model name: W
RJ-4) cross-sectional size: 58, I x 29
, 1 mm) and inserted into a waveguide. The transmittance was measured by keeping the output of the oscillator constant and taking the ratio of the readings on the wattmeter after inserting the sample and before inserting the sample.

Transmission loss (dB) is a value obtained by multiplying the common logarithm of the reciprocal of transmittance by 10.

In the device used this time, the maximum power that reaches the wattmeter before sample insertion is 1.5m1d, and the minimum power that can be read with a -1 wattmeter is 0.1μ, so the minimum measurable transmittance is 0. .007%, maximum transmission loss is approximately /l0d
It is B.

Regarding the reflectance, the ratio S (voltage standing wave ratio) between the maximum value and the minimum value of a standing wave caused by interference between an incident wave and a reflected wave was measured. The reflectance γ was determined from the equation of the relationship between S and the power reflectance γ. However, in the case of a sample with high conductivity, the value of S becomes large, and the measurement accuracy deteriorates because it is more easily influenced by the characteristics of the detector of the standing wave measuring device. Therefore, in this measurement, in order to avoid this, we measured the distance ΔQ between two points where the standing wave power is doubled (4 - times in voltage) on both sides of the minimum point Q min, and calculated S using the following formula. was calculated.

Table 3 shows the measurement results of λg=tube wavelength (9.81 cm at 4.0 OGHz) or more. The test piece NOs shown here correspond to the test piece NOs shown in Table 2 of Example 1.

Table 3 Transmission loss of polypropylene matrix is 0, 10
dB, and mica alone without a plating film of No. 1 has no effect, but No. 3. In the No. 7 test piece, more than 30 dB is achieved. At this time, the weight proportion of nickel in the nickel-plated mica is approximately 50%. The oxidation treatment (No. 5) and the silane coupling treatment (No. 4) of the nickel film deteriorate the shielding properties.

In the molding material filled with No. 10 aluminum fiber, No. 3 aluminum flake, and No. 3 nickel-plated mica, the volume fraction occupied by the filler in No. 10 and No. 11 is 1 in No. 10 and No. 11.
9.9% and No. 3 is 19.1%, No. 3
Although the amount is somewhat lower, it has better shielding properties than aluminum-filled molding materials.

Example 3 High-voltage discharge (25 V to noise source) in an electromagnetic shield room
, 200mA) spark plug, frequency 0~
The shielding effectiveness was measured in the I GHz range.

The distance between the half-wave dipole antenna and the object to be measured is 500m.
m and the received signal was analyzed using a spectrum analyzer. Frequency analysis range 0-200 MHz is 50
For MHz and 0-IGHz, the antennas were tuned to 220 MHz. The test piece was placed in a copper box (soo
N500 x 500mm) front opening (113X
113mm).

Table 4 shows the attenuation (dB). The test piece numbers correspond to those in Table 2. However, the average thickness is 1.16 mm. In addition, an aluminum plate was used as a comparison sample.

Table 4 Molding materials filled with nickel-plated mica flakes exhibit unique damping characteristics compared to aluminum metal plates. Table 4 shows the degree of attenuation at the peak of typical attenuation characteristics. Although the weight percentage of nickel in the nickel-plated mica of Nos. 3 and 7 is about 50%, a considerable shielding effect is observed.

Example 4 A DC motor housed in an iron plate case was rotated by a 3V dry cell battery in an electromagnetic shield room, generating noise radio waves from the brush, and leaking radio waves through a test piece attached to an opening (155 x 60 mm) at 150 volts. The signal was received by a half-wavelength dipole antenna located at a distance of mm, and measured by a spectrum analyzer in the same manner as in Example 1.

Table 5 shows the attenuation (dB). The test piece is No. 0 in Table 2.
It is equivalent to 3.

Table 5 The aluminum plate shows stable attenuation of around 35 dB over the entire measurement wavelength range (θ to I Gl(z)), but the molded product containing nickel-plated mica shows almost the same attenuation as Example 3. Table 5 shows the degree of attenuation at its peak.Depending on the frequency, there are places where only about 5 dB of attenuation can be obtained, but at high frequencies (500 MHz), the average attenuation is 1 dB.
Attenuation of about 5 dB can be obtained.

Example 5 The tensile strength of the electromagnetic shielding material of the present invention was determined. Approximately 1
．． A dumbbell-shaped tensile test piece was cut from a 2 mm thick compression molded plate. Table 6 shows the average values of the seven test pieces.

The tensile speed was 5 mm/min. Test piece Not corresponds to Table 2.

Table 6 Even if the mica surface is coated with a nickel film, the material strength does not decrease. No. surface treated with silane coupling material
The strength of No. 4 is 1.1 times higher than that of No. 3 which is not treated, but the electromagnetic shielding property is low. Nos. 3 and 4 have almost the same volume filling ratio as No. 10 using aluminum fiber, but the material filled with nickel-plated mica shows superior values in both strength and elastic modulus.

Example 5 Mica coated with nickel (metalization rate 53%) was added to polypropylene at a ratio of 55% by weight and mixed for 6 minutes at 230° C. in a Gravender Plastomill to obtain a filler volume fraction of 25%. % electromagnetic shielding material was prepared. This material was then compression molded at 220° C. for 5 minutes to form a 2 mm thick sheet. The volume resistivity of this material is 5
．． It was 1×10 −1 Ω·cm.

Table 7 shows the electric field shielding characteristics and magnetic field shielding characteristics of the samples thus obtained.

Table 7 Example 6 Nickel-coated mica with a metallization rate of 45% was mixed with a volume fraction of 1
An electromagnetic shielding material was prepared in the same manner as in Example 5 by blending various thermoplastics in proportions of 5%, 20% and 25%. Table 8 shows the results of measuring the volume resistivity and electromagnetic wave transmission loss (4 GHz) of these materials.

Table 8 Example 7 An electromagnetic shielding material was prepared in the same manner as in Example 6 using thermosetting plastics such as epoxy resin, unsaturated polyester resin, and phenol resin as the plastics.

Table 9 shows the results of measuring the volume resistivity and electromagnetic wave transmission loss (4HGz) of these materials.

Table 9

Claims (4)

[Claims] (1) An electromagnetic shielding material made of inorganic powder and plastic that has a metal film firmly adhered by chemical plating on its surface. (2) The electromagnetic shielding material according to claim 1, wherein the inorganic powder is mica. (3) The electromagnetic shielding material according to claim 1 or 2, wherein the metal film is nickel. (4) The electromagnetic shielding material according to claim 1, which contains at least 10% by weight of inorganic powder.