JP4765936B2 - Painted steel plate with excellent heat dissipation - Google Patents

Description

  The present invention relates to a coated steel sheet suitable for a housing (referring to an outer box-like body) such as a home electric appliance that generates heat inside, a radiator plate, or the like.

  From the viewpoint of preventing global warming due to carbon dioxide, energy saving is being promoted for all types of equipment, whether industrial or life related. For example, in an air conditioner, energy saving is achieved by increasing the size of a radiator of an indoor unit or an outdoor unit or increasing the air volume.

  Even in refrigerators and personal computers, the amount of heat generated from compressors and CPUs (central processing units) tends to increase due to the recent increase in size of refrigerators and the increase in computing speed of personal computers. It is required to dissipate.

  In the case of a refrigerator, a radiator is used to dissipate the heat generated by the compressor, and forced convection by a fan such as an air conditioner is not performed. Conventionally, the radiator is in direct contact with the external air, and the heat generated by the compressor is directly dissipated from the radiator to the external air. However, from the viewpoint of design, most of the heatsinks are currently stored inside, and the heat generated inside is transferred from the heatsink in the order of compressor → heatsink → heatsink. Dissipated. Therefore, current refrigerators have a structure that is less likely to dissipate heat than conventional ones.

  Heat dissipation from the heat sink (ie heat transfer to the outside air) is due to convection and radiation. Of these, the effect of convection is small. This is natural convection heat transfer with a small air movement (flow) because the refrigerator is used indoors and the back surface to which the heat sink is usually attached is used close to the wall. . Therefore, in the dissipation of heat from the heat sink, the contribution of heat transfer by radiation is large. Therefore, if the heat dissipation of the heat sink is excellent, the heat exchange efficiency of the entire refrigerator is improved and the power consumption is reduced. In addition, the life of the electrical parts is extended.

  In the case of a personal computer (especially a desktop personal computer), the amount of heat generated from the CPU is greatly increased due to a remarkable increase in the computation speed in recent years, and the heat dissipation is a big problem. Usually, a fan is used to dissipate heat, but there is a problem that noise increases when the rotational speed is increased to increase the air volume. Also in this case, if the amount of heat transfer by radiation from the housing of the personal computer can be increased, the heat generated inside can be quickly dissipated outside without increasing the rotational speed of the fan.

  As a technique for improving the heat dissipation at about 150 ° C. or less, which is required for housings and heat sinks of home appliances, Patent Document 1 discloses a surface treatment material excellent in thermal radiation. This surface treatment material is a surface treatment material (preferably a metal plate) having a thermal emissivity α calculated by the following equation (1) of 60% or more.

Since the radiant heat from the housing such as the heat sink and the home appliance has a peak at a wavelength of 8 to 10 μm, the outer layer coating film among the coating films formed on the surface of the base material is one or more layers.
A pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm;
A pigment having a thermal emissivity of 60% or more at a wavelength of 12 μm;
Since these pigments complement the heat radiation characteristics, a higher heat radiation property can be obtained than when they are used alone. For example, a material containing carbon black having a high thermal emissivity at a wavelength of 6 μm and titania having a high thermal emissivity at a wavelength of 12 μm in a predetermined amount and / or a predetermined mass ratio It is suitable for a heat sink and the like, and is economically advantageous.

  In Patent Document 2, an outer layer coating and an inner layer coating are provided on the surface of the substrate, and the inner layer coating contains a predetermined amount of a pigment having a thermal emissivity α calculated by the above formula (1) of 70% or more. A surface treatment material (preferably a metal plate) containing the inner layer coating film having a thermal emissivity of 70% or more is disclosed.

  In addition, Patent Document 3 discloses a far-infrared coating composition that can be colored and a far-infrared heater as a technique related to the improvement of thermal radiation. In this technique, at least a far-infrared radiation pigment among a far-infrared radiation pigment, a color pigment, or a coating layer reinforcing agent is contained in a vehicle (color developing agent) containing silicon alkoxide, metal alkoxide, a mixture thereof, or a partial condensate. It relates to a far-infrared paint composition to be contained, and a far-infrared heater having a far-infrared radiation layer formed using this far-infrared paint composition, and as a far-infrared radiation pigment, graphite, oxide, boride, carbide, nitriding Compounds, fluorides, silicon compounds, phosphorus compounds, sulfur compounds or chlorides, each alone or as a mixture, or composite compounds.

Patent Document 4 describes a far-infrared radiation material composed of a plurality of far-infrared radiation pigments that efficiently radiate far-infrared rays in a wavelength range that is easily absorbed by moisture contained in biological tissues such as animals and plants and human bodies. Yes.
JP 2002-226783 A JP 2002-228085 A Japanese Patent Laid-Open No. 1-259073 Japanese Patent Publication No.7-115914

  As described above, conventionally, improvement of heat dissipation of materials has been performed mainly by increasing the thermal emissivity of a coating film (paint). However, no clear investigation has been made on the influence of the substrate.

  On the other hand, when a coated steel plate is applied to a casing of an electronic device, electromagnetic shielding properties are required as an important performance of the casing. Therefore, the electrical resistance value of the inner side of the housing, that is, the surface opposite to the coating film surface of the coated steel plate (that is, the back surface) is required to be small. In consideration of such a practical use method, a coating film having a high thermal emissivity cannot always be applied to the back surface, and sufficient heat dissipation may not be obtained.

  It is an object of the present invention to provide a coated steel sheet having excellent heat dissipation, excellent electrical conductivity and excellent electromagnetic shielding properties, and suitable for a housing, a radiating plate, etc. of home appliances that generate heat inside. It is said.

  Here, “thermal emissivity” and “thermal emissivity” mean “thermal emissivity” and “thermal emissivity” of the material surface (plated surface or coated surface), unless otherwise specified. The degree of the heat radiation effect from the high temperature side to the low temperature side when the plated steel plate or the coated steel plate as a whole or when the coated steel plate is assembled into a housing is called “heat dissipation”.

  The present inventors have investigated the heat dissipation characteristics of a metal plate as a coating base (base material), and compared with an aluminum plate and a pure galvanized steel plate (electrogalvanized steel plate (EG) and hot dip galvanized steel plate (GI)). The present inventors have found that the heat dissipation of the alloyed hot-dip galvanized steel sheet (GA) is good.

  Further, in the above practical use form (that is, a form used in a state where a coating film having a high thermal emissivity is formed on the outer surface of the casing), the galvannealed steel sheet (GA) is used. By setting the surface opposite to the coating film (that is, the inner surface of the housing) in the state of a metal plate or plating layer, or having a thin film rust-proofed, It has been found that it is possible to obtain sufficient heat dissipation and conductivity necessary to ensure electromagnetic shielding properties.

  Furthermore, while a coated steel sheet in which an alloyed hot-dip galvanized steel sheet (GA) is used as a coating base is excellent in heat dissipation, plating peeling called enamel hair tends to occur during shearing. In order to solve this problem, a detailed study was conducted on a plating composition capable of suppressing plating peeling while maintaining excellent heat dissipation, and the present invention was completed.

  The gist of the present invention resides in the following coated steel sheets (1) to (4) and electronic equipment (5) in which the coated steel sheets are used as constituent members.

  (1) A coated steel sheet having two or more layers formed on one surface, the coated base material is an alloyed hot-dip galvanized steel sheet (GA), and the thermal emissivity of the other surface is 40% or more. Painted steel sheet.

  In the coated steel sheet of (1), the total thickness of the two or more coating films is preferably 10 μm or more.

  (2) A coated steel sheet having two or more layers formed on one side, the coated base material being an alloyed hot-dip galvanized steel sheet (GA), and the outermost layer of the two or more layers. One or both of a pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm and a pigment having a thermal emissivity of 60% or more at a wavelength of 12 μm are contained in one or more layers other than the outer layer. Painted steel plate.

  (3) A coated steel sheet having two or more layers formed on one side, the coated base material being an alloyed hot-dip galvanized steel sheet (GA), and the outermost layer of the two or more layers. A coated steel sheet in which at least one of titania and carbon black or both pigments are contained in one or more coating layers other than the outer layer.

  In the coated steel sheet of (2) or (3), the total thickness of the two or more coating films is preferably 5 μm or more.

  Furthermore, in the coated steel sheet of (1) to (3), the thickness of the coating film other than the outermost layer on the surface on which the coating film is formed is 10 μm or less, and the thickness of the entire coating film is 50 μm or less. If it is, since generation | occurrence | production of peeling of a coating film, a crack, etc. can be suppressed, it is preferable.

  (4) A coated steel sheet having two or more layers formed on one side, the coated base material is an alloyed hot-dip galvanized steel sheet (GA), and the other side is coated with an inorganic coating or an inorganic-organic composite coating. Painted steel sheet.

Here, “inorganic coating”, which will be described in detail later, refers to chromate treatment, phosphate-based treatment, treatment containing silicon and silicate, etc., and “inorganic organic composite coating” refers to the inorganic coating described above. Refers to a treatment in which an organic resin such as a water-soluble phenol resin is blended.
Moreover, the coated steel plate (4) may satisfy at least one of the above (1) to (3). That is, the thermal emissivity of the other surface is preferably 40% or more. The “two or more coating films” are pigments having a thermal emissivity of 60% or more at a wavelength of 6 μm in one or more coating films other than the outermost layer of the two or more coating films. And either or both of pigments having a thermal emissivity of 60% or more at a wavelength of 12 μm may be contained. Further, at least one of titania and carbon black or both pigments may be contained in one or more coating films other than the outermost layer of the two or more coating films. Here, the total thickness of the two or more coating films can be 10 μm or more (in the case of (2) and (3) above, it can be 5 μm or more). Furthermore, among the two or more coating films, the thickness of the coating film other than the outermost layer can be 10 μm or less, and the thickness of the entire coating film can be 50 μm or less.

  (4) In the coated steel sheet, the layer formed by the inorganic coating or the inorganic-organic composite coating contains one or more elements selected from Si, P, V, Al, Mg, Mo, Zr and Ti. If so, Cr is not contained in the layer, which is preferable from the viewpoint of environmental protection.

  In the coated steel sheet of (4), a pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm and a pigment having a thermal emissivity of 60% or more at a wavelength of 12 μm are applied to the inorganic coating layer or the inorganic / organic composite coating layer. It is also preferable that either or both of these are contained.

In the coated steel sheet of (4), if the adhesion amount of the inorganic coating layer or the inorganic / organic composite coating layer is 10 mg / m ² or more and 1500 mg / m ² or less, good corrosion resistance and conductivity are compatible.

  Further, in the coated steel sheet of (4), it is preferable that the surface resistance value on the surface opposite to the surface on which the coating film is formed is 5Ω or less because conductivity is ensured in addition to corrosion resistance.

  In the coated steel sheet according to any one of (1) to (4), it is preferable that the thermal emissivity of the surface on which the coating film is formed is 80% or more.

In the coated steel sheet according to any one of (1) to (4), if the galvannealed steel sheet (GA) corresponds to any one or more of the following (a) to (c): It is possible to suppress the occurrence of enamel hair (plating peeling) during shearing.
(A) The product of the plating adhesion amount (g / m ² ) and the Fe concentration (% by mass) in the plating film is 450 or less.
(B) The Al concentration in the plating film is 0.25% by mass or more.
(C) Si content in base material steel is 0.02-0.2 mass%.

  (5) An electronic device in which the coated steel sheet according to any one of (1) to (4) is used, and the surface on which the coating film is formed is directed toward the outside of the device. .

  “Electronic equipment” as used herein refers to home appliances such as air conditioners, lighting fixtures, refrigerators, OA equipment such as personal computers and copiers, AV equipment such as TVs and videos, automobile electrical equipment, and other industrial and daily life. Refers to related electronic equipment.

  The coated steel sheet of the present invention has excellent heat dissipation and electromagnetic shielding properties, and is suitable as a material for housings, heat sinks, etc. of home appliances, personal computers, and other electronic devices that generate heat internally. .

It is a longitudinal cross-sectional view which shows typically the layer structural example of the coated steel plate of this invention. It is a figure which shows schematic structure of the principal part of the radioactive evaluation apparatus of a coated steel plate. It is a figure which shows schematic structure of the principal part of the conductivity evaluation apparatus of a coated steel plate.

Explanation of symbols

1: Base steel plate 2: Alloyed hot-dip galvanized layer 3: Chemical conversion film 4: Inner layer coating film 5: Outer layer coating film 6: Coating layer 7: Sample 8: Simulated casing 9: Constant temperature bath 10: Vent 11: Exhaust Hole 12: Heat source 13: Gasket 14: Sample 15: Soldering

  Hereinafter, the coated steel sheet of the present invention will be described in detail. Note that “%” for the Fe concentration, Al concentration, and component content of the base steel in the plating film means “mass%”.

  FIG. 1 is a longitudinal sectional view schematically showing a layer configuration example of the coated steel sheet of the present invention. As shown in FIG. 1, a base steel plate 1 is coated on both sides with an alloyed hot dip galvanized layer 2, and a chemical conversion film 3 is applied on the coated surface side, which is the front (front) surface. The inner layer coating film 4 is formed thereon, and the outer layer coating film 5 is further formed thereon. In this example, a coating layer 6 formed of an inorganic coating or an inorganic-organic composite coating is provided on the back side. Note that the coating layer 6 may be omitted or a pretreatment film such as a chemical conversion film by a coating base treatment. Below, the structure of each layer of the coated steel plate of this invention is demonstrated in order.

1. Painted base material In the coated steel sheet of the present invention, an alloyed hot-dip galvanized steel sheet (GA) is used as a coated base material (paint base).

  The heat dissipation of the alloyed hot-dip galvanized steel sheet (GA) is better than, for example, the case of using a normal electrogalvanized steel sheet (EG) or hot-dip galvanized steel sheet (GI). In the case of applying coated steel plate to the above-mentioned usage form (that is, using the coating layer facing the outside of the housing and the plating layer or the surface subjected to the antirust treatment of the thin film facing the inside) This is because it is particularly advantageous in heat dissipation.

  Specifically, as shown in the examples described later, the thermal emissivity is about 13% in the hot dip galvanized steel sheet (GI), and about 46% in the galvannealed steel sheet (GA). High value.

  Although this mechanism is not clear, for example, the hot galvanized film is mainly composed of a pure metal phase, whereas the alloyed hot dip galvanized film is mainly composed of an intermetallic compound. Inferred.

  In addition, electromagnetic shielding properties are required for electronic equipment casings. If a coated steel sheet using an alloyed hot-dip galvanized steel sheet (GA) as a coating substrate is applied to the electronic equipment casing, electrogalvanization is possible. This is more advantageous than the case where a steel plate (EG) or a hot-dip galvanized steel plate (GI) is used as the coating substrate.

  This is because the surface of the alloyed hot-dip galvanized steel sheet (GA) has unique micro unevenness, so that when it is coated on the back surface for rust prevention, it adheres as an average value in the surface. Even if the amount is large, since the coating layer enters the concave and convex portions, the actual film thickness of the coating layer that becomes an obstacle to conductivity becomes thinner than in the case of other plating types. That is, it is considered that when the coating layer thickness is thin, the convex portion is not completely covered, and the plating surface may be locally exposed.

However, a coated steel sheet using a galvannealed steel sheet (GA) as a coating base is likely to have enamel hair during cutting. This is plating peeling caused by low adhesion between the base steel plate and the galvannealed layer. When there is a strong demand for prevention of enamel hair, it is necessary to use an alloyed hot-dip galvanized steel sheet (GA) in which one or more of the following measures (i) to (iv) are taken. Good.
(i) Lower the Fe concentration in the plating film.
(ii) Reduce the amount of plating adhesion.

These measures (i) and (ii) are effective in suppressing enamel hair because they have the effect of suppressing stress acting on the interface between the plating layer and the steel sheet. However, if the Fe concentration is too low, the state of the plating film becomes close to that of the hot dip galvanized film, which is disadvantageous in terms of heat dissipation. Further, if the plating adhesion amount is too small, it is disadvantageous with respect to corrosion resistance. When taking the measures (i) and (ii) above to prevent enamel hair, as described above, as a measure of balance between enamel hair suppression and heat dissipation and corrosion resistance, the Fe concentration in the plating film is as follows. It is preferable that the product of (%) and plating adhesion amount (g / m ² ) be 450 or less. In addition, when the Fe concentration in the plating film and the plating adhesion amount are viewed individually, the preferable range of the Fe concentration is 7% or more and 10% or less, and the preferable range of the plating adhesion amount is 25 g / m ² or more and 45 g / m. About ² or less and an upper limit, More preferably, it is 35 g / m ² or less.

(iii) The Al concentration in the plating film is increased.
Since the higher the Al concentration in the plating film, the more effective the adhesion between the plating layer and the steel plate is. Therefore, the measure (iii) is more effective for enamel hair suppression. Preferably, the Al concentration in the plating film is 0.25% or more. However, if the Al concentration in the plating bath is increased excessively in an attempt to increase the Al concentration in the plating film, there is a concern that the alloying process speed will be reduced and the productivity will be affected. The following is preferable.

(iv) A small amount of Si is contained in the base steel.
By containing a small amount of Si in the base steel, the adhesion between the plating film and the steel sheet is improved, and the generation of enamel hair during shearing can be effectively suppressed. When the measure (iv) is taken to suppress enamel hair, the preferable range of the Si content is 0.02% or more. However, when there is too much Si content, problems, such as a steel plate becoming hard and difficult to process, will arise. Therefore, when the measure (iv) is adopted to prevent enamel hair, the content is made 0.02 to 0.2%. A more preferred upper limit is 0.1%. Therefore, for example, when workability is important, the Si content of the base steel should be reduced as much as possible, and measures (i) to (iii) should be taken as necessary.

  In addition, the preferable range about content of another steel component is as follows.

  C may be determined according to required mechanical characteristics. In general, if the content increases, the strength of the steel can be secured, but it has adverse effects such as age hardening. Therefore, the C content is preferably as small as possible and is preferably less than 0.01%. More preferably, it is 0.003% or less (corresponding to the C content of the ultra-low carbon steel).

  Mn is the main element used to secure the strength of steel in place of C, but it is better if the application to the housing of electronic equipment, which is the main use of the coated steel sheet of the present invention, is better. The Mn content is preferably 0.3% or less. It is preferable to adjust the amount of Mn added according to the required strength of the base steel plate.

  P is an element used for fine adjustment of the strength of the steel, but since segregation or the like often affects the surface properties of the steel sheet, it should be kept as low as possible, and its content should be 0.02% or less. Is preferred. More preferably, it is 0.01% or less.

  S forms inclusions with Mn and other elements, and often serves as a starting point for processing cracks during the forming process of a steel sheet. Therefore, the S content should be controlled as low as possible, preferably 0.01% or less, more preferably 0.005% or less.

  Further, for example, Ti, Nb, B or the like may be included for improving workability, and other elements may be included as necessary.

2. Coating surface (paint base treatment)

  In order to improve the long-term durability of coated steel sheets, such as corrosion resistance and coating film adhesion, chromate treatment and phosphate treatment, and recently proposed treatments that do not use chromate (for example, organic treatment) , Silica-based treatments, composite treatments thereof) and the like may be subjected to a coating ground treatment (pre-painting treatment), and that is preferable.

Adhesion amount of the coating pretreatment coating that case, if the chromate conversion coating, 5 to 200 mg / ^{m 2} reckoned as metal chromium, and more preferably from a 20 to 100 mg / ^{m 2.} Moreover, if it is a phosphate treatment film, it is good to set it as 0.2-5 g / m < ² >, More preferably 0.5-3 g / m < ² >. Moreover, in the case of the coating ground treatment which does not use chromate, the total adhesion amount is preferably 10 mg / m ² or more and 1000 mg / m ² or less. What is necessary is just to set according to the coating adhesiveness and corrosion resistance requested | required.

  [Coating]

  In the coated steel sheet of the present invention, two or more coating films are formed on one surface of the above-described coated base material (the surface subjected to the above-described coating ground treatment).

  As described above, the coated steel sheet of (1) is “a coated steel sheet having two or more layers formed on one side, and the coated base material is an alloyed hot-dip galvanized steel sheet (GA). The surface has a thermal emissivity of 40% or more. ”

  Among the two or more coating films, the thermal emissivity in one or more coating films other than the outermost coating film (that is, one or more coating films in the lower layer than the outermost coating film) High pigment (exactly, a pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm or a wavelength of 12 μm) is preferable because high heat dissipation can be obtained. When the coating film in the lower layer than the coating film of the outermost layer is a plurality of layers, the pigment having a high thermal emissivity may be contained in any layer.

  The coated steel sheet (2) or (3) is a steel sheet having such a structure (that is, a pigment having a high thermal emissivity is contained in one or more coating films other than the outermost coating film). Of these two or more coating films, the outermost coating film is referred to herein as “outer coating film”, and one or more coating films other than the outermost coating film are referred to as “inner coating film”. The case where two layers of coating films (an outer layer coating film and a single inner layer coating film) are formed will be described as an example.

(A) Inner layer coating film Generally, radiant heat from household appliances such as a heat sink of a refrigerator or a housing of a personal computer has a peak in a wavelength region of 8 to 10 μm. Therefore, if the inner coating film contains a pigment having high thermal emissivity in the vicinity of this peak, for example, both wavelength regions (wavelength 6 μm and wavelength 12 μm) sandwiching this peak, the thermal radiation of the coating film surface As a result, the heat dissipation of the coated steel sheet is improved.

The coated steel sheet of the above (2) is a steel sheet having such a structure, and “a coated steel sheet having two or more layers formed on one side, and the coated base material is an alloyed hot-dip galvanized steel sheet (GA). , and the and in the inner layer coating, either or both of the pigment thermal emissivity is 60% or more of the pigment and the wavelength of the thermal emissivity of 60% or more of at least wavelength 6μm is 12μm Inclusion Is a steel plate.

Here, “thermal emissivity at a wavelength of x μm” means β _x represented by the following equation (2).

  A pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm or a wavelength of 12 μm (these pigments are also referred to herein as “thermal radiation pigments”) is effective even if one of them is contained. However, if both are included, these pigments complement each other's thermal radiation characteristics, so that the effect of improving thermal radiation is greater than when they are contained alone. In addition, the thermal radiation pigment should just have thermal emissivity satisfy | fill said conditions, and there is no restriction | limiting in the kind itself. In addition, a pigment other than the heat-radiating pigment may be included.

  In this coated steel sheet, the coated base material is an alloyed hot-dip galvanized steel sheet (GA), and both the heat dissipation and electromagnetic wave shielding properties are good.

  The coated steel sheet of (3) is “a coated steel sheet having two or more coating films formed on one side, the coated base material is an alloyed hot-dip galvanized steel sheet (GA), and in the interior coating film Further, at least one of titania and carbon black or both of the pigments is contained in the steel sheet.

  This coated steel sheet is a case where the thermal radioactive pigment is titania and carbon black in the coated steel sheet of (2). Carbon black has a thermal emissivity almost similar to that of a black body in the wavelength range of 6 μm or less, and has a high thermal emissivity at a wavelength of 6 μm, and titania has a thermal emissivity almost similar to that of a black body at wavelengths of 12 μm or more. Therefore, it has a high thermal emissivity at a wavelength of 12 μm.

  Carbon black and titania are both versatile and cheaper and have a higher thermal emissivity than other highly heat-radiative pigments, so if you use carbon black and titania, heat dissipation is possible without increasing costs. An excellent coated steel sheet can be obtained. In this case also, pigments other than carbon black and titania may be included.

  If the ratio of the mass of carbon black to the mass of titania (hereinafter referred to as “carbon black / titania”) is 0.01 to 0.30 (1% to 30% in terms of percentage), excellent thermal radiation is obtained. Since the surface which has it can be easily obtained with a highly versatile pigment, it is preferable. When carbon black / titania is less than 1%, the thermal radiation characteristics are close to those when titania is contained alone, and the thermal radiation in the region where the wavelength is 6 μm or less is not sufficient. On the other hand, when carbon black / titania exceeds 30%, the heat radiation characteristics are close to those of carbon black alone, and the heat radiation in the region where the wavelength is 12 μm or more is inferior. In addition, even if the content of carbon black is as small as about 1% of the content of titania, such a heat radiation characteristic is exhibited because carbon black has a very excellent concealing property. This is thought to be due to concealing heat radiation.

  It is effective if the pigment (pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm or a wavelength of 12 μm, carbon black, titania) is contained even a little. However, in order to easily obtain a remarkable effect, the total content of these pigments is preferably 5% by mass or more based on the dry mass of the inner coating film. Moreover, it is preferable to set it as 70 mass% or less so that the workability of a coating film may not be impaired. More preferably, it is 8-60 mass%.

In the coated steel sheet containing carbon black and titania, the inner coating film may contain a pigment having a high thermal emissivity other than carbon black and titania. The thermal radiation pigment is not particularly limited, but is preferably a pigment that is safe, excellent in water resistance and weather resistance, and maintains the thermal radiation effect over a long period of time. Among them, alumina (Al ₂ O ₃ ), zirconia (ZrO ₂ ), silica (SiO ₂ ), zircon (ZrSiO ₄ ), magnesia (MgO), yttria (Y ₂ O ₃ ), cordierite (2MgO · 2Al ₂ O ₃ · 5SiO _{2), β-spodumene (Li 2 O · Al 2 O} 3 · 4SiO 2), mullite _{(Al 2 O 3 · 3SiO 2} ), aluminum titanate _{(Al 2 O 3 · TiO 2} ), tourmaline [WX ₃ B ₃ Al ₃ (AlSi ₂ O ₉ )] ₃ (O, OH, F) ₄ ] or the like is preferably used. When these pigments are contained, the total content of these pigments added to carbon black and titania is preferably 5% by mass or more based on the dry mass of the inner layer coating film.

  As a binder for holding the above-mentioned heat-radiating pigment and various pigments described later, that is, a binder used for a coating film formed on the substrate surface, it is difficult to cause yellowing, discoloration, gloss reduction, chalking, etc., and has been used for many years. Even so, it is preferable to use an organic resin that maintains the aesthetics and can maintain the concealing effect for a long period of time.

  Examples of such a resin include an acrylic resin, a polyester resin, a polyolefin resin, and a fluororesin. If necessary, a melamine-based, benzoguanamine-based, or isocyanate-based crosslinking agent may be included. Any one of these resins may be used, but two or more kinds may be mixed and used.

  The content of these resins is preferably 10 to 90% by mass with respect to the dry mass of the inner layer coating film. From the viewpoint of suppressing enamel hair, the inner layer coating film should have a lower glass transition temperature, and preferably, for example, 30 ° C. or lower.

  In addition to the above, the inner layer coating film may contain a thickening agent such as synthetic fine silica, organic bentonite, carboxymethyl cellulose, polyvinyl alcohol, or a dispersant such as polyacrylic acid or polyacrylate.

  Improved anti-corrosion pigments necessary for obtaining desired coating properties such as corrosion resistance, adhesion between the substrate surface and organic resin (eg, polyester resin, fluororesin, etc.) and the cohesive strength of the coating itself For example, extender pigments such as silica, alumina, calcium carbonate, barium sulfate, kaolin clay, talc, nepheline sinite, mica, and bubble-containing pigments may be included.

  The thickness of the inner layer coating film is preferably about 3 to 10 μm. This is because if it is too thin, the coating film adhesion and processability are poor, and if it is too thick, the above-mentioned enamel hair tends to occur.

  As mentioned above, although the case where the two-layer coating film (the outer-layer coating film and the one-layer inner-layer coating film) is formed on one surface of the coated substrate has been described as an example, the inner-layer coating film may be two or more layers. .

  The coated steel sheet of the present invention preferably has a thermal emissivity of 80% or more on the coating surface. The thermal emissivity is obtained from the above equation (1). In the present invention, the wavelength region is 2.5 μm to 25 μm.

  Since organic resins generally have absorption in the infrared region (in other words, the thermal emissivity is high in this region), the thermal radiation improves as the coating thickness increases. Specifically, the total thickness of the two or more coating films is preferably 10 μm or more (as described later, when the inner coating film contains carbon black and / or titania, 5 μm or more). In the coated steel sheet having such a coating film, in the examples described later, the thermal emissivity of the coating film surface was 80% or more and was excellent in heat dissipation.

(B) Outer layer coating The outermost layer coating contains various colored pigments in order to adjust the color. Furthermore, other pigments, thickeners, dispersants, and the like may be included. Aluminum flakes may be blended to form a metallic coating film, or a matting agent may be blended to form a matte coating film. Depending on the color tone of the surface, carbon black, titania and other heat-radiating pigments may be contained.

  The average particle size of the pigment is preferably 50 μm or less from the viewpoint of enhancing the stain resistance, weather resistance, and coloring stability of the coating film. More preferably, it is 20 micrometers or less, More preferably, it is 10 micrometers or less.

  As the binder resin, it is preferable to use an acrylic resin, a polyester resin, a polyolefin resin, a fluororesin, or the like that can maintain an aesthetic appearance. The content of these resins is preferably 10 to 90% by mass with respect to the dry mass of the coating film (outer layer coating film), like the inner layer coating film.

  The thickness of the outer coating film is preferably 5 μm or more. This is because it is effective in concealing the inner coating film and stabilizing the hue of the coated steel sheet. Another reason is that the thicker the coating film, the higher the thermal emissivity. More preferably, it is 7 μm or more.

  As described above, the total thickness of the coating film is preferably 10 μm or more. On the other hand, when the total thickness of the coating film exceeds 200 μm, peeling or cracking of the coating film may occur when processing the surface treatment material, and in some cases, multiple coating operations are required. It becomes economically disadvantageous. More preferably, the upper limit of the total thickness of the coating film is 50 μm.

  Therefore, in the coated steel sheet of (1) to (3), if the thickness of the inner layer coating film on the surface on which the coating film is formed is 10 μm or less and the total thickness of the coating film is 50 μm or less, The occurrence of peeling and cracking of the film can be suppressed, which is preferable.

3. The other surface where the coating film is not formed In the coated steel sheet of the present invention, the other surface where the coating film is not formed (hereinafter referred to as “back surface”) is defined by the coated steel sheet of (1), It has a function of “thermal emissivity of 40% or more”. When the coated steel sheet of (1) of the present invention is used as a casing of an electronic device, the back surface is used with the heating element on the side. At this time, it is advantageous that the back surface has a high thermal emissivity. In this steel plate, the plated surface may be exposed, or a state in which some rust prevention treatment is performed. As described above, the thermal emissivity is about 46% for the alloyed hot-dip galvanized steel sheet (GA) and about 13% for the hot-dip galvanized steel sheet (GI). For example, it can be said that the thermal emissivity of the surface is good, and it can be expected that the heat dissipation of the coated steel plate itself, or the heat dissipation when assembled to the housing or heat sink of electronic equipment, will be significantly improved. .

  The state in which the plated surface is exposed is superior in electromagnetic wave shielding properties because it has better conductivity. However, if the plated surface is left exposed, white rust or red rust may be generated on the surface in the process from manufacture to assembly, which may impair the appearance. Further, if there is any contamination (for example, attachment of human fingerprints) in the process up to assembly, the contamination remains on the plating surface. Therefore, it is better to have some rust prevention treatment.

  The coated steel sheet of (4) is “a coated steel sheet having two or more layers formed on one surface, the coated base material is an alloyed hot-dip galvanized steel sheet (GA), and the other surface (that is, , The back surface) is coated with an inorganic coating or an inorganic-organic composite coating.

  The back surface defined by the steel plate of (4) is provided with an inorganic coating or an inorganic-organic composite coating as a rust prevention treatment. In this case, it is optional whether or not it has the function of “thermal emissivity of 40% or more” defined by the coated steel sheet of (1), but the coated steel sheet is provided in the casing of an electronic device having an electromagnetic wave source inside. In consideration of the need for electromagnetic shielding properties, it is preferable to provide both functions by balancing the antirust function and the heat radiation.

  Here, the “inorganic coating” refers to a chromate treatment, a phosphate-based treatment such as zinc phosphate, and a treatment containing silicon and silicate formed by an alkali silicate or a sol-gel method. Say. In any case, a rust prevention function can be imparted to the back surface of the coated steel sheet.

  The “inorganic organic composite coating” is a process in which an organic resin such as a water-soluble resin (for example, a water-soluble phenol resin) or an emulsion (for example, an acrylic resin) is blended in the inorganic coating, and has a rust-proof function. Can be further improved. However, adding a large amount of organic resin improves corrosion resistance and the difficulty of remaining fingerprints (fingerprint resistance), but it is not preferable for electrical conductivity, so the mixing ratio is based on the total amount of inorganic / organic composite coating treatment. The content is preferably 50% by mass or less.

  In the coated steel sheet (4), the layer formed by the inorganic coating or the inorganic-organic composite coating is preferably a layer not containing Cr. Examples of such a layer include those containing one or more elements selected from Si, P, V, Al, Mg, Mo, Zr and Ti. A preferred treatment mode (treatment system) in which a coating layer containing these elements is formed is exemplified below.

[Processing system in which layer to be formed contains Si]
A liquid to which an alkali silicate (for example, Li silicate) or a silane coupling agent (for example, γ-glycidoxypropyltrimethoxysilane or 3-aminopropyltrimethoxysilane) is added is applied.

[Treatment system in which layer to be formed contains P]
A widely used treatment system such as zinc phosphate is used. In addition, a treatment system in which an aqueous solution such as primary aluminum phosphate or primary magnesium phosphate is directly applied to the plating surface can be used.

[Processing system in which layer to be formed contains V]
An aqueous solution containing ammonium vanadate, ammonium metavanadate, or the like, or a chemical solution containing nitric acid, phosphoric acid, or fluorine ions added thereto is applied and dried.

[Treatment system in which the layer to be formed contains Al]
A dispersion containing water-soluble aluminum hydroxide or feathery alumina sol (amorphous boehmite) is applied and dried. Alternatively, as described above, a liquid containing another anion salt (in this case, primary phosphate) such as primary aluminum phosphate may be used.

[Treatment system in which the layer to be formed contains Mg]
The liquid to which Mg alkoxide is added is applied to the plating surface. Or the said liquid is made to react with a plating surface. Moreover, you may use the liquid containing other anion salts (in this case, primary phosphate) like the said primary magnesium phosphate.

[Processing system in which the formed layer contains Mo]
Nitric acid, phosphoric acid, cation (Mg ²⁺ , Al ³⁺ ) or the like is added to the aqueous solution containing molybdate, and the reacted liquid is applied to the plating surface and dried.

[Treatment system in which the layer to be formed contains Zr]
A solution to which Zr alkoxide, basic Zr carbonate, Zr fluoride, Zr-containing organic chelate or the like is added is applied to the plating surface and dried.

[Treatment system in which the layer to be formed contains Ti]
Ti alkoxide or basic Ti carbonate, Ti fluoride, Ti-containing organic chelate, Ti-containing coupling agent (compound in which organic functional groups such as epoxy group, vinyl group, amino group, methacryloxy group are bonded to Ti alkoxide) The added liquid is applied to the plating surface and dried.

  In these treatment forms, as described above, an appropriate amount of organic resin may be blended in the treatment liquid.

  These preferable treatment systems may be used alone. However, for example, two or more liquids are used in combination, and the coating amount is reduced by further improving the corrosion resistance (thereby improving the conductivity), and the contradictory performance of conductivity and corrosion resistance is high. It is more preferable if both performances can be balanced and balanced.

  In order to increase the thermal emissivity of the back surface in the layer formed by the coating layer forming treatment, the thermal radiation pigment described above may be included, more specifically, either one or both of carbon black and titania. Good. At this time, if the particle size of the heat-radiating pigment is too large, the corrosion resistance is deteriorated, so that it is preferably about 0.5 μm or less.

  You may add the electroconductive powder for improving electroconductivity, for example, metal powder, such as Zn and Ni, and particles, such as graphite, to the layer formed by the said coating layer formation process. However, since corrosion resistance may be deteriorated, the content in the coating layer is preferably 10% by mass or less, more preferably 5% in combination with the above-mentioned heat-radiating pigment. In addition, when using these conductive powders, in consideration of dispersibility in the coating layer to be formed, an organic functional group (epoxy) is added to the surface of the alkoxide of Si, Ti, Al, Zr in advance. Group, vinyl group, amino group, methacryloxy group, etc.) are preferably reacted.

In the coated steel sheet of (4), if the adhesion amount of the inorganic coating layer or the inorganic / organic composite coating layer is 10 mg / m ² or more and 1500 mg / m ² or less, good corrosion resistance and conductivity are compatible.

  In addition, in the coated steel sheet of (4), if the surface resistance value of the surface opposite to the surface on which the coating film is formed (that is, the back surface) is 5Ω or less, in addition to corrosion resistance, to ensure electromagnetic shielding properties. It is preferable because necessary conductivity is also ensured.

  The “surface resistance value” in this case is a value measured using the apparatus shown in FIG. Specifically, the sample is placed above and below the metal mesh gasket (for example, “EGU-0505” manufactured by Foam Kasei Co., Ltd.) so that the back surface is in contact with the gasket. It is a resistance value calculated by measuring a voltage when a current of 100 mA is applied in a state where a surface pressure of 2.9 N (300 gf) is applied in addition to the weight of the sample.

  The electronic device of (5) is an electronic device in which the coated steel sheet described in any of (1) to (4) is used, and the surface on which the coating film is formed is placed outside the device. "Electronic devices used for".

  In these electronic devices, the most frequently used form of coated steel sheet is the use as a member constituting a box-shaped body (that is, an electronic device casing) outside the electronic device main body. It can also be used as a member surrounding a specific part of the main body.

  At that time, the coated surface of the present invention described in the above (1) to (4) is made of alloyed molten zinc. Plated steel sheet (GA) is used as a base, and one side is painted, and the back side is treated with, for example, a thin rust-proof treatment. It has excellent heat dissipation and electromagnetic shielding when assembled in a housing. . Therefore, it is suitable as a housing for home appliances, OA equipment, AV equipment, etc., and other industrial and life related electronic equipment.

4). Manufacturing method The manufacturing method of the coated steel plate of the present invention described above is not particularly limited. For the painted surface, for example, the above-described pigment having a high thermal emissivity and other pigments, a thickener, a dispersant and an organic resin are dispersed in a solvent to form a coating composition, and this coating composition is applied to the substrate surface. The coating may be applied and dried to form an inner coating film, and then a coating composition mainly containing a color pigment for the outer coating film may be applied thereon to form an outer coating film.

  The solvent used for the preparation of the coating composition may be a commonly used solvent, and may be selected appropriately from water, toluene, xylene, cyclohexanone, methyl ethyl ketone, etc. according to the organic resin used.

  The coating composition may be applied by a conventionally used method, for example, spray coating, roll coating, curtain flow coating, bar coating, or the like. After painting, it may be dried and cooled using known equipment and methods such as a hot air oven or induction heating oven.

  Moreover, what is necessary is just to process as follows about the inorganic coating or inorganic-organic composite coating of a back surface.

[Reactive coating treatment]
Reactive coating treatments such as reactive chromate treatment and zinc phosphate treatment are performed after the coated substrate (ie, alloyed hot-dip galvanized steel sheet (GA)) is immersed in a chemical solution heated to room temperature or heated, or sprayed. It can be carried out by washing with water.

  However, since it is difficult to make a separate coating surface and back surface (selection processing) with these treatments, both the function of the painted surface as a paint ground treatment and the antirust function of the back surface (including conductivity) are compatible. Used only when possible. Therefore, the following coating type coating treatment is preferable because of its design flexibility.

[In the case of coating type coating treatment]
It can be carried out by coating-type chromate treatment or inorganic coating or inorganic-organic composite coating treatment containing one or more elements selected from Si, P, V, Al, Mg, Mo, Zr and Ti. In particular, when the coating surface treatment on the painted surface is different from the coating treatment on the back surface, it is preferable because the back surface can be coated by a roll coating method. Moreover, also about the drying after application | coating, it can dry with well-known facilities and methods, such as a hot air oven and induction heating oven.

( Reference Example 1: Effect of plating type on heat dissipation)
A plated steel sheet having a base material of a cold-rolled steel sheet (thickness: 0.6 mm) having the chemical composition shown in Table 1 is used as a coating base material. A coated film was formed on the painted surface, and a coated steel plate was prepared on the other surface (back surface) without any treatment, and the heat dissipation of the coated steel plate and the thermal radiation of the back surface were evaluated.

[Plating type]
Two types were used: a hot-dip galvanized steel sheet (reference “GI”) and an alloyed hot-dip galvanized steel sheet (reference “GA”).

Hot-dip galvanized steel sheet (GI)
Al concentration of plating layer: 0.40%,
Amount of plating: 60 g / m ² on both painted and back surfaces
Roughness of plating surface: Centerline average roughness Ra 0.60 μm
Alloyed hot-dip galvanized steel sheet (GA)
Al concentration of plating layer: 0.25%,
Fe concentration: 8.5%
Plating adhesion amount: 45 g / m ² on both painted and reverse surfaces
Roughness of plating surface: Center line average roughness Ra 0.68 μm

[Paint surface treatment]
A chemical solution (“EC2000” manufactured by Nippon Paint Co., Ltd.) was applied to the painted surface so that the adhesion amount after drying was 60 mg / m ² and dried at a steel plate temperature of 80 ° C. for 10 seconds.

[Coating formation]
An inner coating film and an outer coating film were sequentially formed by the following method on the surface subjected to the coating ground treatment. As a pigment to be included in the inner layer coating film, carbon black having an average particle size of 0.02 μm (“MA-100” manufactured by Mitsubishi Chemical Corporation, referred to as “CB”) and an average particle size of 0.25 μm. Titania (Ishihara Sangyo Co., Ltd. "Taipeku CR-90", code | symbol "CR") was used.

  One or both of these pigments CB and CR are dispersed and mixed using a ball mill together with a polyester resin and a melamine-based crosslinking agent as a dry solid content and a solvent (using an appropriate amount of cyclohexanone), and contain these pigments Five types of coating compositions for inner-layer coating films (paints 1 to 5) shown in Table 2 were obtained including those that were not used. In addition, the mixing ratio of the melamine-based crosslinking agent with respect to the polyester resin was 5 to 20 parts by mass with respect to 100 parts by mass of the polyester resin in Examples 1 to 4.

  These paints 1 to 5 are applied to the base material surface that has been subjected to the above-mentioned coating base treatment by a roll coating method so that the dry film thickness is 5 μm, and subjected to a baking treatment at 220 ° C. for 60 seconds on the base material surface. An inner coating film was formed.

  In addition, as a pigment to be included in the outer layer coating film, a white pigment having an average particle diameter of 0.25 μm (the “CR”) and a red pigment having an average particle diameter of 0.2 μm (“Red Light 6300” manufactured by Mitsubishi Materials Corporation). “, Sign“ RL ”) was selected and toning was performed.

  30 parts by mass of the white pigment CR, 3 parts by mass of the red pigment RL, and 67 parts by mass of a polyester resin and a melamine-based crosslinking agent as a dry solid content are dispersed and mixed in the same manner as in the case of the inner layer coating film, A coating composition (coating material) for an outer layer coating film was obtained.

  This paint was applied to the surface of the formed inner layer coating film by a roll coating method so that the dry film thickness was 16 μm, and subjected to baking treatment at 240 ° C. for 60 seconds to form an outer layer coating film. Obtained.

  Samples are cut out from each of these coated steel sheets, and the heat radiation performance of the coated steel sheets is evaluated with the radiation evaluation apparatus shown in FIG. 2, and in order to clarify the effect of the plating type on the heat radiation performance of the coated steel sheets, no coating is applied. The thermal emissivity of the back surface was measured.

[Evaluation method of heat dissipation]
As shown in FIG. 2, the radioactive evaluation apparatus is a rectangular parallelepiped with a sample (painted steel plate) 7 attached to the upper surface, the other five surfaces made of a heat insulating material, and a thermostatic chamber that can accommodate the simulated case 8. 9 is provided. A heat generation source 12 is provided in the simulated housing 8. The thermostatic chamber 9 is painted black inside and has a vent hole 10 and an exhaust hole 11 for constant exhaust on the side. In addition, the arrow in a figure represents the direction of airflow. Thermocouples for measuring the temperature of each part are arranged in the part denoted by A in the figure inside the simulated housing 8 and the part designated by B in the figure in the thermostatic chamber 9. Yes.

  In the evaluation of heat dissipation, the inside of the thermostatic chamber 9 was adjusted to a predetermined temperature (23 ° C. in the present embodiment) while performing constant evacuation, and the sample 7 was placed with the painted surface facing outward on the upper surface of the simulated housing 8. After the heating of the heat source 12 in the simulated housing 8 is started, the temperature difference between the simulated housing 8 and the thermostatic chamber 9 (temperature difference between the part A and the part B) becomes constant. Until the temperature difference was obtained. This temperature difference was used as an index of heat dissipation. That is, the one where the said temperature difference is smaller has shown that it is easy to radiate | emit the heat | fever from a heat-generation source outside, and can evaluate that heat dissipation is favorable.

[Measurement method of thermal emissivity]
Using an infrared absorption spectrum measuring apparatus manufactured by BIORAD, a spectral reflection spectrum (R (λ)) in a wavelength region of 2.5 to 25 μ was measured on the back surface side of the coated steel plate. The spectral reflectance spectrum (R (λ)) was substituted into the above equation (1) to obtain the thermal emissivity α.

  The survey results are shown in Table 3. In Table 3, paints 1 to 5 in the column of “inner layer coating film” correspond to paints 1 to 5 shown in Table 2. Further, “heat dissipation” is a temperature difference (temperature difference as a heat dissipation index) in the simulated housing and the thermostatic chamber measured by the above-described radioactivity evaluation apparatus.

  As shown in Table 3, the sample using the alloyed hot-dip galvanized steel sheet (GA) as the coating substrate was excellent in heat dissipation. Such excellent heat dissipation results from the fact that the thermal emissivity of the back surface (that is, the plated surface) is higher than that of the hot dip galvanized steel sheet (GI).

  As the paint for the inner coating film, when the paint 5 not containing a pigment having a high thermal emissivity was used (No. 9, 10), and the paints 1 to 4 containing a pigment having a high thermal emissivity were used. When compared with the cases (No. 2, 4, 6, 8), the heat dissipation was better when the paints 1 to 4 were used.

( Reference Example 2. Effect of coating thickness on heat dissipation)
The galvannealed steel sheet (GA) used in Example 1 was used as a coated substrate, to the substrate surface, forming a coating film on one surface (coated surface) obtained in Reference Example 1 Thus, a coated steel plate was produced without performing any treatment on the other surface (back surface). The heat dissipation of the coated steel sheet and the heat radiation of the front and back surfaces were evaluated. The evaluation method of heat dissipation and heat radiation is the same as in Reference Example 1.

  The results are shown in Table 4. In Table 4, paint 3 and paint 5 in the column of “inner layer coating film” correspond to paint 3 and paint 5 shown in Table 2.

  As shown in Table 4, in the case of a coating film containing no titania or carbon black (No. 16, 17), the total thickness of the coating film is about 10 μm or more (No. 17), and the coating film containing titania or carbon black. In the case of (No. 11-15), when the total thickness of the coating film was 5 μm or more, the thermal emissivity was secured by 80% or more, and good heat dissipation was obtained. (No. 11, 13-15)

(Example 1 : Relationship between back surface rust prevention treatment and conductivity, heat dissipation and corrosion resistance)
Using the hot-dip galvanized steel sheet (GI) and alloyed hot-dip galvanized steel sheet (GA) used in Reference Example 1 as the coating base material, the coating surface treatment layer and inner layer are applied to the painted surface in the same manner as in Reference Example 1. A coating film (using paint 3 in Table 2, thickness 5 μm) and an outer layer coating film were formed.

The back side was created separately as shown in the column “Back side” in Table 5 to be described later. In other words, roughly divided ・ Plating surface (as plated) (No.18, 19)
・ Inorganic coating or inorganic-organic composite coating (No. 22 to 47)
-Coating film (Coating ground treatment was applied in the same manner as in Reference Example 1, and an inner layer coating film having a thickness of 5 μm was formed using the coating material 3 in Table 2. In Table 5, it is described as coating material 3) (No .20, 21)
There are three types.

The coated steel sheet thus produced was evaluated for its heat dissipation, heat radiation on the back surface, conductivity and corrosion resistance. The evaluation method of the heat dissipation and the thermal radiation of the back surface is the same as in Reference Example 1.

[Evaluation method of conductivity]
The surface resistance value was measured using the apparatus shown in FIG. Sample 14 (100 mm square) is placed above and below the gasket 13 through a gasket 13 (“EGU-0505” manufactured by Foam Kasei Co., Ltd.) in which a metal mesh is wound around an insulating material so that the back surface is in contact with the gasket 13. When a lead wire is connected to the end face of each sample 14 by soldering 15 and a current of 100 mA is applied in a state where a surface pressure of 2.9 N (300 gf) is applied in addition to the weight of the sample placed on the upper part The surface resistance value was calculated by measuring the voltage.

[Evaluation method for corrosion resistance]
A 70 mm × 150 mm sample was cut from each of the prepared coated steel sheets, the end face was sealed with a polyester tape, and then subjected to a salt spray test specified in JIS Z 2371. After completion of the test, the rusting situation was visually confirmed, and based on the following criteria, it was evaluated as good if it was marked with ◎ or ◯.
(Evaluation criteria for corrosion resistance)
A: Rust area ratio 0% until 72 hours of salt spray test
○: Rust area ratio 10% or less until 72 hours of salt spray test △: Rust area ratio 50% or less until 72 hours of salt spray test X: Rust area ratio 50% or more until 72 hours of salt spray test Table 5 Shown in In Table 5, Cr, Si, Ti, Zr, ALP, and VP in the “Processing type” column of “Back” are obtained by forming a coating layer by the following methods, respectively.

  “Cr”: The coating amount and the concentration were changed so as to obtain a target Cr adhesion amount by coating-type chromate treatment, and a film was formed by a roll coating method. The maximum temperature reached by the steel sheet (hereinafter referred to as “PMT”) was dried at 80 ° C. for 20 seconds.

  “Si”: a coating solution and a concentration of a solution in which 10% γ-glycidoxypropyltrimethoxysilane and 3% water-soluble polyvinylphenol are dissolved as a silane coupling agent so as to achieve a target dry adhesion amount; After applying the chemical solution with a roll coater, it was dried at PMT 100 ° C. for 40 seconds.

  "Ti": Roll coater containing 20% Ti tetraisopropoxide and 5% alcohol-water mixed solution in which water-soluble polyvinylphenol is dissolved. After applying the chemical solution, it was dried at PMT 100 ° C. for 40 seconds.

“Zr”: The coating amount and concentration of an aqueous solution containing 20% (as ZrO ₂ ) and 8% of a commercially available ammonium zirconium carbonate and a polyacrylic acid having a molecular weight of 5,000 are changed to a target dry adhesion amount. After applying the chemical solution with a roll coater, it was dried at PMT 120 ° C. for 30 seconds.

  “ALP”: An aqueous solution obtained by adding 30 parts by mass of a phosphonic acid chelate (30%) to 100 parts by mass of a commercially available first aqueous aluminum phosphate solution (30%), so that the coating amount and concentration are adjusted so as to achieve a target dry adhesion amount. After applying the chemical solution with a roll coater, it was dried at PMT 120 ° C. for 30 seconds.

  “VP”: An aqueous solution obtained by adding orthophosphoric acid to a commercially available ammonium vanadate aqueous solution so that the V / P molar ratio is 1/1 (ammonium vanadate 1%, 0.838% as phosphoric acid), target The coating amount and concentration were changed so that the dry adhesion amount was as follows, and the chemical solution was applied with a roll coater, and then dried at PMT 120 ° C. for 30 seconds.

  “S1”: Carbon black (particle size: 0.08 μm) is further mixed in the solution described in “Si” so as to be 2% in terms of dry solid content, and the solution is used in the same manner as “Si”. And dried.

  “S2”: Carbon black (particle size: 0.08 μm) is further mixed with the solution described in “Si” so that the dry solid content is 5%, and the liquid is used, as in “Si”. And dried.

  “S3”: In the solution described in “Si”, titania (particle size: 0.1 μm) is further mixed to a dry solid content of 2%, and this solution is used in the same manner as “Si”. It was applied and dried.

  “S4”: In the solution described in “Si”, titania (particle size: 0.1 μm) is further mixed to a dry solid content of 5%, and this solution is used in the same manner as “Si”. It was applied and dried.

  “S5”: In the solution described in “Si”, carbon black (particle size: 0.08 μm) is further 3% in dry solid content and titania (particle size: 0.1 μm) is 2% in dry solid content. It mixed so that it might become, and it apply | coated and dried like "Si" using the said liquid.

  As shown in Table 5, the coated steel sheet using the alloyed hot-dip galvanized steel sheet (GA) as the coating substrate was excellent in heat dissipation even when the back surface was subjected to rust prevention treatment. Furthermore, compared with the case where a hot-dip galvanized steel sheet (GI) was used, the corrosion resistance was almost the same, but the conductivity was also excellent. In addition, when a coating film is formed on the back side, any of the base materials used lacks conductivity (No. 20, 21), and the effect of using an alloyed hot-dip galvanized steel sheet (GA) is recognized. (No. 21). Moreover, the thing containing carbon black and titania in the rust-proofing layer on the back side improved the thermal emissivity on the back side and improved the heat dissipation, although it did not contain (No. 48-52). . In addition, the carbon black and titania (No. 52) added with one of them alone was highly effective even at the same amount, and a synergistic effect was also observed.

( Reference Example 3 : Influence of Fe, Al concentration, etc. in plating film on generation of enamel hair)
Cold-rolled steel sheet (thickness: 0.5 to 0.8 mm) having the chemical compositions shown in Table 6 were used galvannealed steel sheet as a base material a (GA) as the coated substrate, the coated surface, reference In the same manner as in Example 1, a coating ground treatment was performed to form an inner layer coating film and an outer layer coating film to prepare a coated steel sheet. In addition, about the inner layer coating film, the coating film 3 of the said Table 2 was used, the film thickness was 5 micrometers, and the same thing as the case of the reference example 1 was used about the outer layer coating film, and the film thickness was 16 micrometers.

  Table 6 shows the amount of adhesion of galvannealed plating, the Fe concentration and the Al concentration in the plating film.

  About these coated steel plates, the occurrence state of enamel hair was investigated.

[Method for evaluating enamel hair]
Shearing was performed by inserting a blade from a painted surface of a coated steel plate having a width of 100 mm with 5% clearance. The state of peeling of the coating film on the end face subjected to shearing was observed, and based on the following criteria, it was evaluated that it was good if it was marked with ◯ or Δ.
(Evaluation criteria for enamel hair)
○: No peeling Δ: The peeling portion is less than 20% of the length of the end face ×: The peeling portion is 20% or more of the length of the end face Table 7 shows the survey results. In Table 7, the average values on both surfaces of the base steel plate were adopted for the plating adhesion amount, the Fe concentration in the plating film, and the Al concentration.

In Table 7, test no. 2-1 and 2-2 have large values of “plating adhesion amount (g / m ² ) × Fe concentration in plating film (%)” (hereinafter referred to as “plating adhesion amount × Fe (%)”). This is an example in which the Al concentration (%) in the plating film (hereinafter referred to as “Al (%)”) is relatively low. In this case, enamel hair was generated.

  In contrast, test no. 2-3 and 2-4 are examples in which the value of “plating adhesion amount × Fe (%)” is small and Al (%) is relatively high. It was. In addition, Test No. 2-5 to 2-7 are examples in which a base steel containing a small amount of Si was used, but almost no enamel hair was generated.

The coated steel sheet of the present invention is excellent in heat dissipation and electromagnetic wave shielding properties, and heat generated inside electronic devices such as home appliances is easily dissipated (radiated), so that the housing of home appliances, personal computers, and other electronic devices can be used. It is suitable as a material for a body and a heat sink. It is easy to cope with the high electromagnetic shielding properties required with the recent refinement of electronic devices and their widespread use, and their fields of use are extremely wide.

Claims (9)

A coated steel sheet having two or more layers formed on one side,
The coated substrate is an alloyed hot-dip galvanized steel sheet,
The other surface has a thermal emissivity of 40% or more, and the other surface has an adhesion amount of 10 mg / m ² or more and 1500 mg / m ² or less, and contains no thermally radioactive pigment and conductive particles. Only the coating or the inorganic organic composite coating is applied, and when the inorganic organic composite coating is applied, the organic component is 50% by mass or less based on the total amount of the inorganic organic composite coating,
Among the two or more coating films other than the outermost layer, at least a pigment having a thermal emissivity of 60% or more at a wavelength of 6 μm and a thermal emissivity of 60% at a wavelength of 12 μm. One or both of the above pigments are contained in a coated steel sheet. A coated steel sheet having two or more layers formed on one side,
The coated substrate is an alloyed hot-dip galvanized steel sheet,
The other surface has a thermal emissivity of 40% or more, and the other surface has an adhesion amount of 10 mg / m ² or more and 1500 mg / m ² or less, and contains no thermally radioactive pigment and conductive particles. Only the coating or the inorganic organic composite coating is applied, and when the inorganic organic composite coating is applied, the organic component is 50% by mass or less based on the total amount of the inorganic organic composite coating,
A coated steel sheet, wherein at least one of titania and carbon black or both pigments are contained in one or more coating films other than the outermost layer of the two or more coating films. The coated steel sheet according to claim 1 or 2, wherein the total thickness of the two or more coating films is 5 µm or more. Wherein the coating film is formed faces, there is the 10μm or less thickness of the coating film other than the outermost layer, first to third term the claims total thickness of the coating is equal to or is 50μm or less Coated steel sheet according to any of the above. The layer formed by the inorganic coating or the inorganic-organic composite coating contains one or more elements selected from Si, P, V, Al, Mg, Mo, Zr, and Ti. The coated steel plate according to any one of to 4 . The coated steel sheet according to any one of claims 1 to 5, wherein a surface resistance value of a surface opposite to the surface on which the coating film is formed is 5Ω or less. The coated steel sheet according to any one of claims 1 to 6, wherein the surface on which the coating film is formed has a thermal emissivity of 80% or more. The coated steel sheet according to any one of claims 1 to 7 , wherein the galvannealed steel sheet corresponds to any one of the following (a) to (c): .
(A) The product of the plating adhesion amount (g / m ² ) and the Fe concentration (% by mass) in the plating film is 450 or less.
(B) The Al concentration in the plating film is 0.25% by mass or more.
(C) Si content in base material steel is 0.02-0.2 mass%. It is the electronic device in which the coated steel plate in any one of Claims 1-8 is used, Comprising: The surface in which the said coating film was formed is used toward the outer side of the device, Electronic equipment.

Images