JP5534664B2 - Surface-treated metal material excellent in electromagnetic wave shielding property and casing for electronic equipment using the same - Google Patents

Description

  The present invention relates to a metal material that can be suitably used for a housing of an electronic device and has an excellent electromagnetic wave shielding property at a joint, and an electronic device housing manufactured using at least a part of the metal material. In particular, the present invention relates to a metal material and a housing that can effectively suppress malfunction of an electronic device due to radiation noise.

  Electromagnetic waves have been used for broadcasting, radar, ship communication, microwave ovens, etc. for some time, but in recent years, their use has expanded dramatically due to remarkable developments in information and communication technology. Among them, the use of the GHz band that enables transmission of large-capacity information has increased rapidly, and cellular phones (1.5 GHz), ETC (5.8 GHz), satellite broadcasting (12 GHz), wireless LAN (2.45 to 60.0 GHz) ), A rear-end collision prevention radar (76 GHz) and the like have come to be used.

  On the other hand, in addition to conventional cable wiring, in general homes, the arrival of a ubiquitous society in which personal computers, televisions, and various information appliances are networked by wireless communication using microwaves and millimeter waves and are always connected to computers.

  In this way, a large number of electromagnetic wave generation sources surround us, and coupled with the reduction in size, speed, and thinning of communication devices, the radiation of unwanted electromagnetic waves and the resulting risk of malfunction are considered to have increased significantly. It is done.

  There is an electromagnetic wave shielding technique using a metal material as means for suppressing unnecessary electromagnetic wave radiation (Emission) and making it difficult to malfunction even when receiving unnecessary electromagnetic wave radiation (Immunity).

  Non-patent document 1 describes that a metal material is suitable as an electromagnetic shielding material. The electromagnetic wave shield described in the present invention is an “electromagnetic shield” referred to in Non-Patent Document 1, and should be distinguished from an “electrostatic shield” and a “magnetic shield”. That is, an effect of preventing electromagnetic waves having a frequency of about 1 MHz or more from leaking through the material. In this sense, the metal material has an electromagnetic wave shielding effect that is significantly superior to, for example, plastic.

  By enclosing the generation source of unnecessary electromagnetic waves with a metal material, the emission is suppressed, and by enclosing the electronic circuit with a metal material, it becomes an immunity means for protecting the circuit from unnecessary radiation from the outside. Therefore, if an electronic device casing without gaps or joints can be made of a metal material, a good electromagnetic wave shield can be obtained, and electromagnetic wave leakage hardly poses a problem.

  However, the electronic device casing has some joints by screwing, spot welding, helix folding, or the like. Further, the surface of the metal material may be coated with a film containing an organic resin for the purpose of imparting corrosion resistance and fingerprint resistance. In such a case, electromagnetic waves may leak from the joint, and the electromagnetic shielding properties of the housing are determined by the amount of leakage from the joint. Therefore, even a metal material requires a technique for improving the electromagnetic wave shielding property.

The prior art which aimed at the electromagnetic wave shielding property improvement of a metal material is illustrated. In Patent Document 1, the centerline average roughness _Ra is large in a surface-treated steel sheet in which an organic and / or inorganic film not containing chromium is formed on the surface of a zinc-based or aluminum-based plated steel sheet. That is, a method for providing a surface-treated steel sheet having excellent electromagnetic wave shielding properties and corrosion resistance by forming a film on a plated steel sheet with unevenness to make the distribution of the film thickness non-uniform is disclosed. It is stated that the conductivity of the film is determined at the part where the film thickness of the convex part is thin, so that the above configuration is excellent in electromagnetic shielding properties and that good corrosion resistance can be obtained even if the film is non-uniform. ing.

  In Patent Document 2, a steel plate having a roughened surface and a steel plate having a surface layer formed with a plating having a film thickness of 2 μm or less mainly composed of a metal selected from Ni, Cu, Al, Zn, and Sn, It is disclosed that it has excellent electromagnetic shielding properties. Electromagnetic waves are reflected by the unevenness on the surface of the steel sheet, and the electromagnetic waves are attenuated by increasing the path length due to the unevenness, and the electromagnetic waves are also attenuated by the reflection of electromagnetic waves at the plating / steel sheet interface by forming a plating layer. It is disclosed.

  Patent Document 3 discloses a conductive surface-treated steel sheet in which a discontinuous film made of a resin is formed on a plated steel sheet surface via a chromate film.

  Patent Document 4 discloses an electromagnetic wave shielding material in which a conductive coating layer made of Ag, Cu, Au, Al or the like and a magnetically permeable coating layer made of Ni, Fe or the like are alternately laminated on the surface of a steel plate. Since electromagnetic waves are composed of an electric field component and a magnetic field component, the technical idea is to shield the electric field component with a conductive coating layer and the magnetic field component with a magnetically permeable coating layer. A similar technique can also be found in Patent Document 5.

  The prior art of the electromagnetic wave shield other than a metal material is illustrated. Patent Document 6 discloses an electromagnetic wave shielding film and an electromagnetic wave shielding paint made of flaky conductive powder and a binder resin. It is stated that the conductive powder is preferably silver, copper, nickel, cobalt or silicon steel having an aspect ratio of 10 to 250, and the film thickness of the electromagnetic wave shielding film should be 10 to 100 μm.

  Patent Document 7 discloses an electromagnetic wave shielding material that includes an absorbing material that absorbs electromagnetic waves, and in which an electromagnetic wave reflecting material is disposed in the gap. It is stated that the electromagnetic wave absorbing material is composed of graphite or carbon black, a cross-linked polymer, a linear polymer and an alkane-based linear low molecule, and the electromagnetic wave reflecting material is a metal powder such as Ni.

  Patent Document 8 and Patent Document 9 disclose electromagnetic wave shielding materials in which coiled carbon fibers are enclosed in microcapsules and dispersed in a matrix. It is stated that various coiled carbon fibers such as C, SiC and TiC can be used as the coiled carbon fiber, and the fiber diameter is preferably 0.05 to 5 μm.

  Patent Document 10 discloses an electromagnetic wave shielding paint in which nickel fine powder and aluminum fine powder are dispersed in a modified silicone resin. It is stated that the electromagnetic shielding effect SE is recognized by the Advantest method (near field).

Patent Document 11 discloses a magnetic shield sheet in which a magnetic layer having an insulating property is provided on a conductive layer made of an iron-based metal sheet or iron-based metal powder and a binder. It is stated that the magnetic shield effect in the KEC method or the Advantest method is 15 dB or more at 0.5 to 10 MHz.
JP 2004-156081 A JP 2002-232184 A JP 63-114635 A JP 2002-35385A JP 2004-169091 A JP 2000-357893 A JP 2002-246785 A JP 2000-31688 A JP 2000-124658 A JP 2004-168986 A JP 2005-142551 A Yasutaka Shimizu “Latest Absorption and Blocking of Electromagnetic Waves” p205-223 Nikkei Technical Books Co., Ltd. Toshio Kudo, EMCJ 89-96 (1990) p. 51-54 Toshio Kudo, Mitsubishi Electric Industrial Times, No. 79 (1990) p. 21-27

However, all of these conventional techniques have problems.
Patent document 1 is the technical content which improves electromagnetic wave shielding property by providing an unevenness | corrugation to the metal material surface.

  However, according to the study by the inventors, when a plated steel sheet having such a structure is manufactured by a continuous electroplating apparatus, the plated crystal is attached to a metallic energizing roll at a portion where the convex film should be thin. There is a concern that flattening may occur due to crushing, and that it is difficult to ensure sufficient thinness of the film.

  Further, in Patent Document 1, there is no particular mention about the arrangement of the convex portions, but if there is a portion where the interval between the convex portions is large, there is a concern that the electromagnetic wave shielding property is lowered.

  Patent Document 2 does not have a chemical conversion treatment film layer and has poor corrosion resistance and fingerprint resistance.

  In Patent Document 3, the corrosion resistance and fingerprint resistance in a portion where there is no resin coating is poor.

  Patent Documents 4 and 5 are obtained by alternately laminating conductive films / magnetic permeable films. Once each thickness is determined, a frequency that can be effectively shielded is also determined, which is determined by international standards. A single metal material cannot handle a wide frequency range. In the first place, in a plane wave, electromagnetic waves are shielded by shielding either an electric field or a magnetic field, so there is no necessity of alternately laminating a conductive film and a magnetically permeable film.

  The electromagnetic wave shielding films of Patent Documents 6 and 7 both contain a conductive substance such as metal powder and carbon black in the binder resin, but the electromagnetic shielding film is thick as 10 to 100 μm. There is a concern that the cost will be high.

  Each of the electromagnetic wave shielding films of Patent Documents 6, 7, 8, 9, and 10 uses a paint containing a conductive substance such as metal powder or carbon black in a binder resin. Considering the case where this is applied to a metal material, there is a concern that it may be difficult to apply the binder resin uniformly while preventing the separation due to aggregation, sedimentation, and lifting of the metal powder or carbon black when the binder resin is applied to the surface. The

  Since Patent Documents 8 and 9 use a coiled carbon fiber, there is a concern that the cost is industrially high.

  Patent Document 11 confirms the magnetic shield effect at 0.5 to 10 MHz, and these methods are not always effective for suppressing leakage of electric field waves up to 30 to 1000 MHz required by the international standard (CISPR). Absent.

  SUMMARY OF THE INVENTION Accordingly, an object of the present invention is to solve the above-described problems in the prior art and to provide a metal material and a casing excellent in electromagnetic wave shielding properties capable of effectively suppressing malfunction of an electronic device due to radiation noise.

  In order to solve the above-mentioned problems, the present inventors diligently studied the electromagnetic wave shielding characteristics with respect to the electromagnetic wave shielding characteristics from the housing joint.

  As a result, if the energizable portion on the surface of the metal material that constitutes the casing is arranged satisfying the conditions indicated by the present invention at the joint portion of the casing, electromagnetic waves also form the casing at the casing joint portion. As a result, it was found that leakage to the outside of the casing is suppressed by transmitting the inside of the metal material to be excellent, and as a result, the electromagnetic shielding property is excellent, and the present invention has been completed.

The gist of the present invention is the following (1) to (4).
(1) A metal material having at least one surface coated with an insulating film having a thickness of 0.2 μm or more and 8 μm or less made of an organic material, an inorganic material, or both, and the coated surface coated with the insulating film is made of metal. The metal particles are particles having an average particle diameter of 0.1 μm or more and 8 μm or less deposited by electrolytic plating on the metal material, and the metal particles are arbitrarily disposed on the coating surface. When one point is selected, the maximum value of the perimeter (CT) of the shortest triangle that is in contact with the three energizable portions at the three vertices is 5 μm or more and 700 μm in an arbitrary triangle including the point inside A surface-treated metal material excellent in electromagnetic wave shielding properties, characterized by the following:

  (2) In a cross section cut by a line segment having a length of 1 mm arbitrarily selected on the surface of the surface-treated metal material, energization existing on a straight line and a cross-sectional curve obtained by averaging the envelope undulation curve of the surface portion is possible. The surface-treated metal material having excellent electromagnetic shielding properties as described in (1) above, wherein the standard deviation (SH) of the distance to the part is 2.5 μm or less.

(3) the tin metal particles deposited by electrolytic plating, chromium, characterized by more Rukoto either zinc, (1) or electromagnetic shielding properties in excellent metal material according to (2).

  (4) In the joint portion of the housing for electronic equipment, at least one of the members involved in the joining has a surface excellent in electromagnetic shielding properties according to any one of the above (1) to (3) A casing for electronic equipment having an excellent electromagnetic shielding property, characterized by being a treated metal material.

  An electromagnetic wave generated in an electronic device covered with a metal or alloy casing transmits the surface inside the casing. The depth of surface transmission depends on the skin depth due to the skin effect of the metal.

  The skin depth differs depending on the frequency of electromagnetic waves and the type of metal. For example, when the frequency is 30 MHz, the skin depth of iron is about 6 μm and copper is about 12 μm. The frequency of 30 MHz is the minimum frequency specified by the CISPR standard, which is an international standard that regulates noise generated by electronic equipment, but the skin depth of the metal is smaller at higher frequencies.

  Therefore, if it is a metal material having a thickness of 0.1 mm or more that is usually used as an electronic device casing, there is no practical consideration of leakage due to transmission of electromagnetic waves of 30 MHz or more. The main consideration is leakage of electromagnetic waves from the opening or joint of the housing.

  The present invention provides a metal material having excellent electromagnetic shielding properties and corrosion resistance for preventing electromagnetic wave leakage from a joint, and is used in an electronic device casing, whereby 30 to 1000 MHz required by international standards (CISPR). In addition to radiated noise, it can effectively shield radiated noise up to 10 GHz, which is expected to be generated in the future as the operating frequency is increased, thereby suppressing malfunction of electronic devices. is there.

  As a result, it is possible to omit or simplify the conventional electromagnetic shielding measures for joints, that is, heavy use of gaskets, spot welding, screwing, etc., and provide an electronic device casing that is excellent in productivity and economy. be able to.

The present invention is described in detail below. Said (1) is related with the structure for a surface-treated metal material to show the favorable electromagnetic wave shielding property.
The metal that can be applied in the present invention is not particularly limited as long as it has a shape, dimensions, strength, and workability suitable for a casing of an electronic device or a member in the casing. Steel, aluminum, It is not limited to metals such as magnesium, copper, zinc, nickel, titanium, and alloys thereof, but any metal material that can be roughly considered, such as those obtained by plating these metals with dissimilar metals, or by stacking dissimilar metals. Anything is fine.

  The insulating film used in the present invention is suitable from among films containing one or more organic substances such as organic resins or inorganic substances such as metal oxides from the viewpoint of corrosion resistance, fingerprint resistance, scratch resistance, workability, etc. There is no particular limitation.

  For example, any of water-soluble organic resins, emulsion-type organic resins, and solvent-based organic resins can be used. Specific examples include olefin resins, acrylic resins, ionomer resins, epoxy resins, urethane resins, polyester resins, phenol resins, vinyl acetate resins, and fluorine-based resins such as polytetrafluoroethylene and polyvinylidene fluoride. Examples thereof include resin, polystyrene, polyether sulfone, polyphenylene ether, polyphenyl sulfide, polyamideimide, cycloolefin polymer, and liquid crystal polymer.

  These may be used singly or as a mixture of two or more, or a copolymer (for example, ethylene- (meth) acrylic acid copolymer, (meth) acrylic acid- (meth) acrylic). Acid ester copolymer, etc.), modified with each other (for example, epoxy-modified urethane resin, acrylic-modified ionomer resin, etc.), or modified with another organic substance (for example, amine-modified epoxy resin, etc.) Also good.

  Moreover, as an inorganic substance, you may use what dehydrated-condensed metal alkoxides, such as silanol, and what precipitated metatitanic acid and the metal phosphate on the lower-layer metal surface. In order to improve the characteristics of organic and inorganic hybrid films such as silane coupling agents and organic resin films, inorganic compounds such as oxides, salts and complexes of Si, V, Cr and P, and organic compounds such as tannic acid You may use what was disperse | distributed.

  Although the suitable range of the average thickness of an insulating film is based also on the kind of metal of a foundation | substrate, and the component which comprises an insulating film, 0.2-8 micrometers is preferable. If it exceeds 8 μm, it will be difficult to secure the energizable portion, and the electromagnetic shielding properties will deteriorate. If it is less than 0.2 μm, the performance to be secured by an insulating film such as corrosion resistance, fingerprint resistance, scratch resistance, and workability may deteriorate.

  In order to satisfy the above performance balance more preferably, the coating thickness is more preferably in the range of 0.5 to 1.5 μm.

When the improvement of the electromagnetic shielding property by the surface-treated metal material is examined, the shielding efficiency (SE), which is an index of the electromagnetic shielding property, is expressed as in the formula (I) (Non-Patent Document 2), so that electronic equipment It can be said that, at the joint between the surface-treated metal materials in the housing, the electromagnetic wave shielding property is better as the transfer impedance (Z _tr ) on the surface of the surface-treated metal material constituting the housing is smaller.

SE = k · Z _w / Z _tr ··········.
SE: electromagnetic shielding efficiency, k: proportional constant,
_Zw : spatial impedance, _Ztr : transfer impedance

  The inventors diligently studied a method for reducing the transfer impedance on the surface of the surface-treated metal material. As a result, in the surface-treated metal material, the lower layer metal is exposed in the form of minute dots from the upper film, and electrical contact is made through this point from one metal material constituting the joint to the other metal material. By doing so, the electromagnetic wave shielding property was ensured. A minute dot-like portion in which the lower layer metal is exposed from the upper layer film is referred to as an energizable portion.

  The shape of the energizable portion is not limited, but is preferably large enough to be included in a circle having a diameter of 10 μm. This is because if the diameter is larger than 10 μm, there is no surface film, and the film functions such as corrosion resistance deteriorate. Moreover, it is desirable that the energizable portions are dispersed as uniformly as possible on the surface of the surface-treated metal material.

  Here, in the joint part of a housing | casing, the metal surface between adjacent electricity supply parts is a path | route which electromagnetic waves leak, and transmission of a surface treatment metal material surface is so wide that this path | route is wide. It has been found that the impedance increases.

  Furthermore, the amount of leakage of this electromagnetic wave has a large influence on the amount of leakage from the joint because the wider path has more electromagnetic leakage when a wide path and a narrow path are mixed. There was found. Therefore, among the intervals between adjacent energizable portions, if the interval is smaller than a predetermined interval, the width of the leakage path of the electromagnetic wave having a large influence is small, so that the metal in the joint portion It was found that the transmission impedance on the surface of the material was small and the electromagnetic wave shielding property was good.

  Therefore, among the adjacent energizable parts as described above, especially for those having a large interval, as a means for defining the size of the interval, the point for any one point on the surface of the surface-treated metal material, In any triangle that contains a triangle, there is a large correlation with the circumference (CT) of the triangles (2 and 3 in FIG. 1) that contact each of the three energizable parts (1 in FIG. 1) at their three vertices. I found.

  CT thus obtained is a good indicator of W because geometrically 2W <CT ≦ 3W, where W is the width of the electromagnetic wave leakage path that governs electromagnetic wave shielding.

  As an example of a method for measuring CT, for example, FIG. 1 shows a measurement example using an image obtained by visualizing the energizable portion on the surface of the surface-treated metal material. Among arbitrary triangles (2, 3 in FIG. 1) in contact with the energizable portion (1 in FIG. 1), the length of the triangle (3 in FIG. 1) with the longest circumference (CT) is measured. In this example, the image is measured by visual observation, but of course, image processing using a computer may be performed.

  It is a method to identify the energizable part on the surface of the surface-treated metal material, but it is also possible to identify the energizable part by measuring the resistance value while moving the measurement position finely with a manual prober with a small probe needle tip diameter. it can. As an example of a measurement apparatus that can be used for this purpose, there is a manual prober (model 705B, probe needle tip diameter 2.5 μm) manufactured by Nippon Microtronics. In this case, a threshold value of the measured resistance value is set (for example, 10Ω), and if it is equal to or less than the threshold value, it may be defined as an energizable part.

  As another method for identifying the energizable part, measure the surface of the surface-treated metal material with a microscope having a three-dimensional shape measurement function, perform a calculation process based on the uneven shape and the thickness of the upper film coating, The part where the metal or alloy is exposed can be estimated and specified.

  An example of a measuring apparatus that can be used for this purpose is a Keyence nanoscale hybrid microscope (model VN-8000).

  In this case, the upper layer film adhesion thickness is determined by observing the cross section of the test material with a scanning electron microscope (SEM) or an optical microscope at an appropriate magnification. Collect a minimum of 10 samples from a sufficiently distant position of the metal material, and after embedding and polishing, measure the film thickness by cross-sectional observation at 3 to 5 locations that are not unique to each sample, and obtain a total of 30-50 measurements A method of setting the average value to the film thickness may be used.

  From the experimental results shown in Table 1, the maximum CT value on the surface of the surface-treated metal material is preferably 700 μm or less. As a result of the examination, it was found that the smaller this maximum CT is, the better the electromagnetic wave shielding property at the case joint portion using the metal material. On the other hand, if the maximum CT is larger than 700 μm, the electromagnetic shield with a frequency of 30 to 1000 MHz specified by the CISPR standard has a wide path for leaking from the housing joint to the outer surface, so that the electromagnetic shielding property is inferior. I understood.

  Further, as a feature of electromagnetic wave leakage from the housing joint, it is known that the higher the frequency of the electromagnetic wave, the easier it is to leak, but even in this case, a good electromagnetic wave shielding property can be maintained if CT is short.

The lower limit of the maximum CT is 5 μm or more. Generally, if the maximum CT is shortened, the lower layer metal is exposed, and the coating functions such as corrosion resistance, design properties, fingerprint resistance, and scratch resistance imparted by the insulating coating are lowered. If the maximum CT <5 μm, the continuity of the insulating film is not ensured, and the corrosion resistance, fingerprint resistance, etc. of the film hardly function, so this is a practical lower limit of the maximum CT.

  Said (2) is related with the height of the convex part used as the conduction | electrical_connection part for a surface treatment metal material to show favorable electromagnetic wave shielding property. The energizable part of the surface-treated metal material corresponds to the convex part of the underlying metal, and it is advantageous for the electromagnetic wave shielding property at the joint part of the electronic device casing that the convex part has less variation in height.

  In other words, the surface-treated metal materials are in contact with each other at the joint, but here, when the variation in the height of the convex portion that is the energizable portion is large, only the particularly high convex portion functions as the energizable portion. Therefore, the width of the substantial electromagnetic wave leakage path is increased, and the electromagnetic wave shielding property is lowered.

  As the height of the convex portions is more uniform, more convex portions function as energizable portions, so CT is shortened and good electromagnetic wave shielding properties can be secured.

An index representing the uniformity of the height of the convex portion is defined by using an envelope undulation curve and a cross-sectional curve defined in JIS B0631. That is, a straight line (5 in FIG. 2) obtained by averaging the envelope undulation curve (4 in FIG. 2) of the corresponding surface with respect to a line segment having a length of 1 mm designated at an arbitrary position on the surface-treated metal material surface is assumed. When the distance between the straight line and the peak on the cross-sectional curve higher than the straight line is H ₁ , H ₂ ,..., H _n (6 in FIG. 2), the standard deviation given by equation (2) is Let SH be an index that represents the uniformity of the height of the protrusion (see FIG. 2).

Standard deviation SH = √ (1 / n · Σ (H _i −H _ave ) ² ) (2)
(I = 1, 2,..., N)
(H _ave is the average value of H)

  SH is preferably 2.5 μm or less. When SH exceeds 2.5 μm, the probability that the convex portion functions as the energizable portion decreases, and the electromagnetic shielding property of the joint portion decreases. If SH is 1.5 μm or less, it is more preferable because the convex portion functions efficiently as the energizable portion.

  This is a method for obtaining an envelope undulation curve and a cross-section curve, but using a surface profile output using a stylus-type roughness meter, observing a cross-section of a surface-treated plate under a microscope, and using a microscope having a three-dimensional shape measurement function as an electromagnetic wave shield What is necessary is just to obtain | require a surface profile using any method, such as measuring the shape of the surface treatment metal material surface excellent in property, and outputting a cross-sectional profile, and also calculating | requiring an envelope waviness curve and a cross-sectional curve with a computer.

Said ( 1 ) is further related with the surface shape of the surface treatment metal material excellent in electromagnetic wave shielding property.

  As a means of shortening the maximum CT described above, if metal particles are intermittently arranged on the surface of a metal material and an insulating film is coated thereon, individual particles are exposed from the upper layer film, Is the energizable part. The material of the metal particles is not particularly limited.

The maximum CT can be shortened as the density of the metal particles is higher and the distance between the particles is smaller. As a method of placing such a metallic particles, select a method of depositing particulate metal crystals by electroless plating on a metal plate.

The size of such particles is the average particle diameter of 0.1μm or more 8μm or less. If it is less than 0.1 μm, the particles are covered with an insulating film, so that it is difficult to function as an energizable portion, and it is difficult to confirm whether particles having a particle size of less than 0.1 μm are deposited.

  Large particles exceeding 8 μm may have problems such as excessive metal exposure and poor corrosion resistance, poor adhesion to the lower layer, particles easily falling off, and the appearance of the particles being significantly deteriorated due to the influence of the particles.

  More preferably, when the particle size is 0.3 μm or more and 4 μm or less, the balance between the function as the energizable portion and the corrosion resistance, the adhesion to the lower layer, the appearance, etc. is good.

  Further, if a soft metal such as zinc is used as a lower layer metal material and the above-mentioned particles are arranged on a flat surface pressed by a metal roll, the standard deviation SH described in the above (2) is reduced. It is possible to efficiently provide the energizable part, which is advantageous for electromagnetic wave shielding.

  Said (4) is a housing | casing for electronic devices which uses the surface treatment metal material excellent in the electromagnetic wave shielding property of said (1)-(3) for the junction part at least. Examples of the electronic device casing include digital home appliances such as desktop PCs and digital TVs, copying machines, car navigation devices such as car navigation, car AV, engine room electronic devices, and in-vehicle radar housings. Can be mentioned. Of course, you may use the metal material of this invention for the junction part of housing | casing for mobile products, such as a notebook PC and a mobile telephone.

  The present invention is preferably applied to a case in which a metal material has a case where a joint portion of a housing is screw-fastened, spot-welded, helically folded, or the like. When the joint is melted and joined with no gap as in seam welding, the electromagnetic wave shielding property is ensured, so there is no problem even if the present invention is not applied.

  Hereinafter, examples of the present invention will be described. However, the conditions of the examples are one example of conditions adopted for confirming the feasibility and effects of the present invention, and the present invention is limited to this one example of conditions. Is not to be done. The present invention can adopt various conditions as long as the object of the present invention is achieved without departing from the gist of the present invention.

Example 1
(1) Metal plate The following three types of metal plates were used.
Steel sheet: Cold rolled mild steel sheet with a thickness of 0.8 mm SUS (Stainless steel sheet): SUS304 with a thickness of 1.2 mm
Al (aluminum plate): JIS 3004 with a plate thickness of 0.8 mm

(2) Metal plate provided with a plating layer On the above (1), means for providing a plating layer was selected from the following three types.
EG / Zn (electrogalvanizing): A metal plate was electrolytically plated using a plating bath in which sulfuric acid was added to an aqueous zinc sulfate solution.
EG / Zn-Ni (electro zinc nickel plating): A metal plate was electrolytically plated using a plating bath in which sulfuric acid was added to a mixed aqueous solution of zinc sulfate and nickel sulfate.
HD / Zn (hot dip galvanizing): After immersing a metal plate in a hot dip zinc bath containing 0.20% Al, the amount of adhesion was adjusted with an air wiper, and then cooled and plated.

(3) Surface shape adjustment of metal plate The surface of the above (1) and (2) is flattened by the method of i) or ii) below or not flattened, and further on the surface, the following iii), iv) or Metal particles were arranged by the method v).

i) A metal plate is rolled using a rolling roll having a surface roughness of arithmetic average roughness R _a = 0.4 μm or less according to JIS B0601, and the surface is flattened under a condition of a plate thickness reduction rate of 1.5%.

ii) When electroplating the surface of the metal plate, the plating thicknesses are made to increase sequentially by sequentially passing through 10 plating tanks arranged in the continuous plating line. The surface of the plating is flattened by bringing a metal roll whose surface roughness is arithmetic average roughness R _a = 1.0 μm according to JIS B0601 into contact with each other.

iii) Granular tin was deposited on the surface of the electroplated metal material under the following conditions.
As a solution composition, tin ion 10 g / l, phenol sulfonic acid 50 g / l, surfactant 0.5 g / l, bath temperature 45 ° C., current density 0.5 to 10 kA / m ² , tin adhesion amount 0.5 to 5 g / l The particle diameter to be precipitated was adjusted by changing in the range of m ² .

iv) Granular chromium was deposited on the surface of the electroplated metal material under the following conditions.
As a solution composition, CrO ₃ 50 g / l, H ₂ SO ₄ 0.5 g / l, Na ₂ SiF ₆ 0.5 g / l, bath temperature 50 ° C., current density 0.5 to 10 kA / m ² , chromium adhesion amount 0. The particle diameter to be precipitated was adjusted by changing in the range of 5 to 5 g / m ² .

v) Granular zinc was deposited on the surface of the electroplated metal material under the following conditions.
The solution composition is ZnSO ₄ 375 g / l, sodium sulfate 70 g / l, bath temperature 60 ° C., current density 0.5 to 10 kA / m ² , and zinc deposition amount 0.5 to 5 g / m ^2. The particle size was adjusted.

(4) Insulating film The insulating film was selected from the following five types, U, A, M, PE, and Si, which are emulsion, solvent, and water.
U: Emulsion urethane resin (Dainippon Ink, Hydran HW)
A: Emulsion acrylic resin (Mitsui Chemicals, Almatex)
M: Solvent-based melamine resin (Nippon Paint, Olga Select 100)
PE: Solvent-based polyester resin
(Nippon Paint, UNIPON 400)
To these four kinds of organic resins, 10 mass% of the following colloidal silica was added as a rust preventive pigment.
Colloidal silica (Nissan Chemical, Snowtex series)
The type of colloidal silica was selected according to the type of resin. An average particle size of 20 nm was selected.
Si: 3-aminopropyltriethoxysilane, 3-glycidoxypropyltrimethoxysilane, vanadium oxysulfate,
Titanium hydrofluoric acid, phosphoric acid,
What was mixed at a mass ratio of 9: 0.9: 0.07: 0.05: 0.07 The upper film was applied and dried as follows. That is, the film components were mixed, applied to a metal plate with a roll coater, and dried in a direct fire type drying furnace. The drying conditions (temperature, time) were adjusted appropriately according to the type and film thickness of the film components.

Measurement of Maximum CT CT was measured visually using an image obtained by visualizing the energizable portion of the surface-treated metal material surface as a test material by any of the methods described below. As the maximum CT, CT measurement was performed on an arbitrarily selected 1 mm square area, and the maximum value of the obtained CT was used.

  Although it is the method of specifying the electricity supply possible part in the surface of a surface treatment metal material, either of the following methods (a) and (b) was used depending on the case.

  (A) Using a manual prober (model 705B, probe needle diameter of 2.5 μm) manufactured by Japan Microtronics, energization is performed by measuring the resistance value while moving the measurement position at 5 μm intervals with a manual prober with a small probe needle tip diameter. The possible part was identified. The arrangement of the energizable parts was imaged. CT was measured based on this image.

  (B) The surface of the surface-treated metal material is measured using a Keyence nanoscale hybrid microscope (model VN-8000), which is a microscope having a three-dimensional shape measurement function, and an image showing the uneven shape is obtained. From the result of observing the cross section of the sample with a scanning electron microscope (SEM) at a magnification of 1000 times, the insulating film adhesion thickness was obtained.

  A calculation process was performed based on the surface shape and the insulating film adhesion thickness to estimate and identify a portion where the underlying metal or alloy was exposed, and the arrangement of the energizable portion was imaged. CT was measured based on this image.

(6) Measurement of SH SH was measured using a laser microscope OLS1000 manufactured by Olympus Corporation. Using the surface shape measuring function of OLS1000, a cross-sectional curve of the surface of the test material was obtained, and the cross-sectional curve was subjected to image processing by a computer to obtain an envelope undulation curve. Regarded apex of the convex portion of the profile curve and energizable unit, the distance H ₁ between their electrically energizable portion and envelope waviness _curve, H 2, _..., a H _n determined visually SH based on equation 2 above Calculated.

(7) Measurement of transmission impedance The transmission impedance was measured using ZTR39D made by Mitsubishi Electric Industries as a measurement jig. A detailed description of this jig is found in Non-Patent Document 3. The test material is punched into a disk shape having an inner diameter of 11 mm and an outer diameter of 63 mm, and is mounted on a jig. A cross-sectional view of the jig after mounting is shown in FIG.

  ZTR39D originally has a structure in which a disk-shaped sample is sandwiched between upper and lower outer conductors and a central inner conductor. In this study, the transfer impedance of a film containing organic resin is measured more accurately. Therefore, a ring-shaped conductor (made of gold-plated copper) (10 in FIG. 3) having an inner diameter of 20 mm and an outer diameter of 60 mm (10 in FIG. 3) was prepared and placed on the upper surface of the test material (14 in FIG. 3). And the conductor contact area was widened.

  Further, a Teflon plate (11 in FIG. 3) having a thickness of 3 mm was disposed on the back surface of the test material to prevent conduction from the back surface. In order to improve the reproducibility of the measurement, the test material was squeezed only by its own weight of the upper outer conductor without screwing the upper and lower outer conductors (16 in FIG. 3).

At this time, the average surface pressure on the surface of the test material was 0.06 MPa. The jig was connected to a spectrum analyzer (manufactured by Advantest, R3361A) with a coaxial cable, the frequency of the input side voltage was swept from 1 MHz to 1000 MHz, and the power on the output side was measured. Based on the output power P ₁ measured with the jig set without mounting the test material, the transfer impedance Z at each frequency is calculated from the power P ₂ when the test material is present using the formula (II). _tr was calculated.

Z _tr = 100 × (P ₂ / P ₁ )... Formula (II)

The measurement was performed 5 times per sample, and the average of the three data excluding the highest and lowest was obtained. Using the measured value at a frequency of 100 MHz as a representative value, the difference between the average value of each and the transfer impedance of the standard sample (gold-plated copper plate) was evaluated as follows.
Score 1: Difference in transfer impedance with standard sample at frequency 100 MHz is 0.3Ω or less Score 2: Difference in transfer impedance with standard sample at frequency 100 MHz is more than 0.3Ω, 1.0Ω or less Score 3: Frequency 100 MHz The difference in transfer impedance from the standard sample at 1.0 Ω is more than 1.0Ω, 3.0Ω or less Score 4: The difference in transfer impedance from the standard sample at the frequency of 100 MHz is more than 3.0Ω

(8) Evaluation of electromagnetic wave shielding property An aluminum plate having a thickness of 3 mm was welded to prepare a casing having a side of 550 mm, and an opening of 137 mm × 137 mm was provided only on the upper surface. This was installed in a radio semi-anechoic chamber, and a Schafner comb generator was fixed inside the housing as an electromagnetic wave reference transmission source, and then a pulse wave was transmitted at a frequency of 10 MHz to 1000 MHz at intervals of 10 MHz.

  A soft gasket (SGK5-1 manufactured by Morimiya Electric Co., Ltd.) having a width of 5 mm was placed around the opening. A test metal plate of 150 mm × 150 mm was placed thereon. By placing a receiving antenna at a point 3m away from the case in the horizontal direction and connecting it to a spectrum analyzer, the signal strength of the leaked electromagnetic wave from the case is measured, and the electric field strength of 1 μV / m is 0 dB (reference value). ) As dB.

The measurement was performed three times, and the obtained results were averaged and compared with a VCCI standard value (standard of information technology apparatus class B: 40 dB or less for 30 MHz to 230 MHz, 47 dB or less for 230 MHz to 1000 MHz).
Score 1: conforms to the VCCI standard value at 30 to 1000 MHz Score 2: a measurement value that does not conform to the VCCI standard value is recognized at 30 to 1000 MHz (9) Evaluation of corrosion resistance The test material is 150 mm (L) × 70 mm (W) Cut out and subjected to a salt spray test specified in JIS Z2371 for 20 hours. The area ratio of corrosion products on the evaluation surface of the test material was visually observed and evaluated as follows.
Rating 1: Corrosion area ratio less than 0.5% Rating 2: Corrosion area ratio 0.5% or more and less than 3% Rating 3: Corrosion area ratio 3% or more, or red rust is generated in the case of plated steel sheet Example of the present invention Is shown in Table 1.

  The example of the present invention is a representative example of the prior art and has a large maximum CT. 12 and No3, No.3 where no energizable part can be found on the coating surface. Compared to 6, good corrosion resistance with a corrosion resistance rating of 1 or 2 and good electromagnetic shielding properties with an electromagnetic shielding score of 1 are compatible.

  Further, as shown in Table 1, within the preferred range of the present invention, further excellent electromagnetic shielding properties can be obtained.

(Example 2)
Example No. in Table 1 9, 15, 18, 23, 29 and Comparative Example No. 3 metal plates were used for the desktop PC housing. Measure radiated noise at a frequency of 30 MHz to 1000 MHz at a point 3 m away in a radio semi-anechoic room, and a VCCI standard value (information technology equipment class B standard: 40 MHz or less for 30 MHz to 230 MHz, 47 dB or less for 230 MHz to 1000 MHz) and Compared.

  As a result, Example No. Desktop PCs using metal plates of 9, 15, 18, 23 and 29 satisfy the standards, while From No. 3, radiation noise exceeding the standard value was detected.

A diagram schematically showing the method of defining CT A diagram showing how to measure SH A diagram schematically showing the cross section of the transfer impedance measurement jig

Explanation of symbols

1 Energizable part 2 Arbitrary triangle in contact with energized part 3 Triangle with longest CT (CT measurement object)
4 Cross section curve of metal material surface 5 Straight line obtained by averaging envelope undulation curve of surface cross section curve 6 Distance to point on cross section curve higher than straight line obtained by averaging envelope undulation curve 7 Transfer impedance measuring jig 8 Resistance 9 Inner conductor (top)
10 Ring-shaped conductor 11 Teflon for insulation 12 Inner conductor (lower part)
13 Outer conductor (bottom)
14 Co-test metal plate 15 Hard gasket 16 Outer conductor (upper part)

Claims (4)

A metal material having at least one surface coated with an insulating film made of an organic material, an inorganic material, or both having a thickness of 0.2 μm or more and 8 μm or less, and metal particles are intermittently formed on the coated surface coated with the insulating film. The metal particles are particles having an average particle size of 0.1 μm or more and 8 μm or less deposited by electrolytic plating on the metal material, and any one point on the coated surface. When selected, the maximum value of the circumference (CT) of the shortest triangle that is in contact with the three energizable portions at the three vertices is 5 μm or more and 700 μm or less in any triangle that includes the point. A surface-treated metal material having excellent electromagnetic shielding properties.   In a cross section cut by a line segment having a length of 1 mm arbitrarily selected on the surface of the surface-treated metal material, a straight line obtained by averaging the envelope waviness curve of the surface portion and a current-carryable portion existing on the cross-section curve The surface-treated metal material having excellent electromagnetic shielding properties according to claim 1, wherein a standard deviation (SH) of the distance is 2.5 µm or less.   The metal material excellent in electromagnetic wave shielding property according to claim 1 or 2, wherein the metal crystal particles precipitated by the electrolytic plating are made of any one of tin, chromium, and zinc.   In the junction part of the housing | casing for electronic devices, the surface treatment metal material excellent in the electromagnetic wave shielding property in any one of Claims 1-3 in the at least junction part of at least one member participating in joining. A housing for electronic equipment with excellent electromagnetic shielding properties.

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