JP4449468B2 - Black galvanized steel sheet - Google Patents

Description

  The present invention relates to a black zinc-based plated steel sheet, and more specifically, has excellent heat absorption and heat dissipation, electrical conductivity, electromagnetic wave shielding properties, flat plate corrosion resistance and processed portion corrosion resistance, etc. The present invention relates to a black zinc-based plated steel sheet that can be used without painting and does not contain harmful hexavalent chromium.

  In recent years, with the improvement in performance of electronic devices, the amount of heat generated from a CPU (central processing unit) or the like tends to increase, and the dissipation of the heat has become a major issue. For example, in the case of a personal computer, particularly a desktop personal computer, a fan is usually used for heat dissipation, but there is a problem that noise increases when the rotational speed is increased to increase the air volume. There are also devices that are difficult to mount fans, such as inside car audio. In such a case, if the amount of heat transfer due to dissipation from the housing can be increased, the heat generated from the inside of the device can be quickly dissipated without the fan or without increasing the rotation speed of the fan. Can do.

  From the above viewpoint, attempts have been made to impart heat absorption and dissipation to steel plates. For example, a steel sheet having a coating film containing carbon black and titania as pigments has been proposed (for example, Patent Document 1). This is because the infrared wavelength range where the thermal emissivity of each individual pigment component is maximized is different. By combining these pigments, a coating film showing a high thermal emissivity over a wide wavelength range is formed on the steel plate surface. It is an invention to be formed. When such a steel plate is used as a housing material, heat generated from the inside of the device can be effectively released to the outside through the housing.

  However, in order to obtain a sufficient effect, it is necessary to contain a large amount of pigment. For this reason, the film thickness must be increased, resulting in a problem of high cost. There is also a problem that the electrical resistance on the surface of the steel sheet increases as the film thickness increases. In order to prevent leakage of electromagnetic waves generated from electronic devices, it is necessary to securely ground the housing, and for that purpose, it is important that the electrical conductivity of the steel sheet surface is good. Since prevention of leakage of electromagnetic waves is indispensable for electronic devices, there is a limit to the use of paints containing a large amount of pigments with high thermal emissivity in order to impart heat absorption and dissipation.

  On the other hand, black galvanized steel sheets that have been used for internal parts of copiers, etc., have a black appearance and low reflectivity for visible light, and are higher than normal galvanized steel sheets. It is known to have a thermal emissivity.

By the way, generally the method for forming a black membrane | film | coat on a steel plate is divided roughly into the following.
(A) A method of applying a paint containing a black pigment such as carbon black by a spray or roll coater to form a black film with a film thickness of several tens of μm,
(B) A method of forming a black film by reacting or electrolyzing a previously formed plating layer itself.

However, the black steel plate obtained by the method (a) has a problem of a decrease in conductivity as in the case where a coating film containing a pigment is formed on the above-described ordinary steel plate.
There are various methods classified into the (b) method, but in recent years, a method for forming a black film not containing hexavalent chromium has attracted attention in particular from the viewpoint of environmental protection. For example, a zinc-plated steel sheet is used as the base material, and a metal / oxide composite black film containing nickel and zinc metal, nickel and zinc oxide, and optionally hydroxide is formed on the surface of the zinc-based plating layer. Furthermore, a non-chromium type rust preventive film layer containing a resin, at least a thiocarbonyl group-containing compound and / or a vanadic acid compound, and optionally containing a phosphoric acid compound and / or fine silica is formed on the upper layer. Further, a weldable non-chrome type black-treated zinc-plated steel sheet having an organic resin layer optionally containing a black pigment and / or a rust preventive pigment as an upper layer is proposed (for example, Patent Document 2).

In addition, one or more metals selected from the group consisting of Ni, Co, and Fe are deposited on a metal substrate having Zn on the surface by 30 to 200 mg / m ² substitution deposition, and oxide layers of these metals A surface-treated metal material excellent in black appearance, characterized in that is formed (for example, Patent Document 3).

  (B) All black steel plates by the method are intended to provide a black zinc-based plated steel plate that has been subjected to corrosion resistance treatment instead of chromate treatment. There was a problem that the corrosion resistance was insufficient.

JP 2002-226783 A JP 2000-290783 A JP 2002-47579 A

  The present invention has been made in view of such circumstances, and is economical and has excellent heat absorption / dissipation properties, and has excellent conductivity, electromagnetic wave shielding properties, flat plate corrosion resistance, and processed portion corrosion resistance, and generates heat internally. An object of the present invention is to provide a black zinc-based plated steel sheet that can be used without coating as a casing material of an electronic device that does not contain hexavalent chromium.

The present invention applies a treatment liquid containing phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin on the surface of a zinc-based plated steel sheet that has been blackened and dried. A black galvanized steel sheet having a formed composite film, and further having an organic resin layer formed by applying and baking an organic resin paint on the surface of the composite film.

  According to the present invention, it is possible to obtain a black zinc-based plated steel sheet that does not contain any chromium and is excellent in heat-absorbing and radiating properties, electrical conductivity, electromagnetic wave shielding properties, flat surface corrosion resistance, and processed portion corrosion resistance.

The black zinc-plated steel sheet of the present invention is formed on the surface of the zinc-plated steel sheet that has been blackened, with phosphate ions (PO ₄ ³⁻ ), vanadate ions (VO ₃ ⁻ ), metal ions, α, β-unsaturated. By having a composite film formed by applying a treatment liquid to which a carboxylic acid and a glycoluril resin are added, and further having an organic resin layer on the surface of the composite film, it is possible to absorb and dissipate heat, conduct electricity, and shield an electromagnetic wave. In addition to excellent corrosion resistance, in addition to flat plate portion corrosion resistance, it also has excellent processed portion corrosion resistance when the steel sheet is processed, and can sufficiently withstand practical use in a wide range of applications.

  The blackened galvanized steel sheet used as the base material of the present invention is a galvanized steel sheet or a zinc alloy plated steel sheet, for example, a hot dip galvanized steel sheet, a zinc-aluminum (Zn-5 mass% Al) hot dip plated steel sheet, or zinc- A galvanized steel sheet such as an aluminum (Zn-55 mass% Al) hot-dip galvanized steel sheet is blackened. In particular, since the black film formed by the blackening treatment has excellent adhesion and stable mass production quality, a blackened zinc-nickel alloy-based steel sheet is preferable. The blackening treatment is preferably performed after subjecting the galvanized steel sheet to normal treatment such as hot water washing and alkaline degreasing.

  In the galvanized steel sheet that has been blackened as the base material of the present invention, the surface of the galvanized layer is first blackened to form a black film. The film thickness of the black film is preferably from 0.01 to 0.5 μm, particularly preferably from 0.05 to 0.2 μm. If the thickness is less than 0.01 μm, not only the blackening is insufficient, but there is a case where sufficient heat absorbing / dissipating properties cannot be obtained. If it exceeds 0.5 μm, the adhesion of the black film to the zinc-based plated steel sheet may deteriorate. The thickness of the black film can be confirmed by TEM (transmission electron microscope) observation of a thin film prepared by FIB (focused ion beam processing apparatus) processing or the like.

  The blackening treatment method is not particularly limited. Electrochemical treatment methods such as anodic electrolysis, cathodic treatment, and alternating electrolysis, and treatment methods in which metals such as nickel, cobalt, and iron are substituted and deposited together with oxides of these metals, etc. The general method can be used. By these methods, the surface of the galvanized steel sheet can be blackened by forming a black film mainly composed of an oxide.

From the viewpoint of the stability of the blackening treatment method, an electrozinc-nickel alloy-plated steel sheet having a zinc-nickel alloy layer, for example, chlorate ions (ClO ₃ ⁻ ) of 5 to 100 g / l, sulfate ions (SO ₄ A method in which anodic electrolysis is recommended in an aqueous solution containing ^2- ) in an amount of 10 to 300 g / l, pH 0.5 to less than 3.0, temperature 30 to 75 ° C., and electric quantity 10 to 300 C / dm ² is recommended. The black film formed on the surface of the galvanized steel sheet contains at least a metal containing zinc and an oxide of these metals, and may further contain a hydroxide of these metals. Examples of these metals are zinc and nickel.

The composite coating of the present invention is applied with a treatment liquid in which phosphate ions, vanadate ions, metal ions, α, β-unsaturated carboxylic acid and glycoluril resin are added to the surface of a galvanized steel sheet that has been blackened. For example, the surface of a galvanized steel sheet that has been blackened with a treatment liquid in which a vanadic acid compound, a metal compound, an α, β-unsaturated carboxylic acid, and a glycoluril resin are added to a phosphoric acid aqueous solution. It is formed by applying to and drying.
Total addition of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin of the treatment solution in terms of ease of application of the treatment solution and ease of drying The amount concentration is preferably 10 to 30 mass%. As the solvent, water or a mixed medium of an organic solvent or an inorganic solvent that can be mixed with water is used.
Since the treatment liquid is acidic with the addition of phosphate ions, by applying the treatment liquid, a part of zinc is eluted from the zinc-based plating layer and the zinc ion activity in the treatment liquid is increased. During the subsequent drying, various components in the treatment liquid are concentrated and deposited on the surface of the black film, and phosphate ions, vanadate ions, metal ions, α, β-unsaturated carboxylic acid and glycoluril resin are added. A composite film containing is formed.

  The pH of the treatment liquid is preferably 1.5 to 4, more preferably 2.5 to 3.5. The pH is adjusted, for example, by appropriately adding ammonia. If the pH is less than 1.5, the zinc-based plating may be vigorously dissolved between application of the treatment liquid and drying, and the zinc-based plating and the black film may be damaged. If the pH exceeds 4, various metal ions added to the treatment liquid cannot be present stably, and may precipitate as hydroxides, making application difficult. Application | coating of this process liquid is implemented by a normal method, for example, a roll coater method, a spray method, a bar coater method etc.

  Drying after application of the treatment liquid is preferably 80 to 250 ° C. as a maximum plate temperature. More preferably, it is 100-180 degreeC. Below 80 ° C., the drying time becomes too long, which is inconvenient for coating and drying in a continuous line. A drying temperature of 250 ° C. is sufficient, and raising it more than necessary is a waste of energy.

The adhesion amount of the composite film of the present invention is preferably 0.02 to 1.0 g / m ² . More preferred is 0.05 to 0.5 g / m ² . If it is less than 0.02 g / m ² , the corrosion resistance is insufficient, and if it exceeds 1.0 g / m ² , the surface electrical resistance increases, and the required conductivity and electromagnetic wave shielding properties may not be obtained.

Phosphate ions in the treatment liquid are precipitated as phosphates on the black film during drying, contribute to improving corrosion resistance, and have the effect of stabilizing various metal ion components in the treatment liquid in the treatment liquid. . The amount of the phosphate ion PO ₄ ^3- as the main component in the treatment liquid is added to the treatment liquid such as phosphate ions, vanadate ions, metal ions, α, β-unsaturated carboxylic acid and glycoluril resin. The amount added to each treatment solution is preferably 20 to 85 mass%, particularly preferably 50 to 80 mass%, based on the total amount. If it is less than 20 mass%, the coating with the phosphate formed in the composite film becomes insufficient, and the corrosion resistance may deteriorate. If it exceeds 85 mass%, free phosphoric acid in the composite film will increase, and the corrosion resistance may also deteriorate. In addition, this means that the phosphate ion concentration in the treatment liquid is excessive, which is not economical.

Vanadate ions in the treatment liquid have an effect of contributing to improvement of the corrosion resistance of the composite film. Vanadate ions VO ₃ ^- amount to said treatment liquid, the addition amount of the phosphate ions, vanadate ions, metal ions, alpha, of β- unsaturated carboxylic acid and glycoluril resins, to each of the process solution It is preferable that it is 0.5-20 mass% with respect to the total amount which totaled. More preferably, it is 4-8 mass%. If it is less than 0.5 mass%, the corrosion resistance may be insufficient, and if it exceeds 20 mass%, the corrosion resistance may also deteriorate. This also means increasing the vanadate ion concentration in the treatment liquid, which may cause instability in the treatment liquid and cause a precipitate to be generated during storage of the treatment liquid. . Vanadic acid is preferably added to the treatment liquid in the form of a vanadate such as sodium vanadate, potassium vanadate, or ammonium vanadate.

  The α, β-unsaturated carboxylic acid in the treatment liquid has an effect of improving the adhesion of the composite film to the black film. The amount of α, β-unsaturated carboxylic acid added to the treatment liquid is such that phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin are added to each treatment liquid. It is preferable that it is 2-60 mass% with respect to the total amount which totaled the addition amount. More preferably, it is 10-30 mass%. If it is less than 2 mass%, the effect of improving the adhesion with the black film is insufficient, and as a result, the corrosion resistance of the processed part may be insufficient. If it exceeds 60 mass%, the conductivity and electromagnetic wave shielding properties may deteriorate. Examples of the α, β-unsaturated carboxylic acid include acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, and fumaric acid.

  The glycoluril resin in the treatment liquid has an effect of remarkably improving the adhesion with an organic resin layer, for example, a polyester resin layer, which will be described later, provided on the surface of the composite film. The amount of glycoluril resin added to the treatment solution was the sum of the amount of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin added to the treatment solution. 1-20 mass% is preferable with respect to the total amount. More preferred is 5 to 15 mass%. If it is less than 1 mass%, the adhesive improvement effect with an organic resin layer is inadequate, and as a result, processed part corrosion resistance may become inadequate. If it exceeds 20 mass%, the conductivity and electromagnetic wave shielding properties may deteriorate.

The glycoluril resin is a monomer represented by the following structural formula, a polymer of the monomer, a condensate of the monomer, or a mixture of the monomer, a polymer of the monomer, and a condensate of the monomer. .
Examples of the monomer include derivatives in which methylol, butyrol, etc. are added to all or part of the 1-, 3-, 4-, 6-amino group of glycoluril, and the derivatives are further methylated, methyl / ethylated, butylated. The alkyl etherified derivative etc. which were made to mention etc. can be mentioned.
Examples of the condensate of the monomer include an oligomer obtained by condensation via a methylol group or the like.
Preference is given to tetramethylolated glycoluril and its oligomers, which are excellent in water solubility and have good stability in the treatment solution.

（式中、Ｒ^１〜Ｒ^４はＨ、またはＣ_n Ｈ_2n+1で示されるアルキル基、またはＣ_nＨ_2nＯＨ、またはＣ_n Ｈ_2nＯＣ_m Ｈ_2m+1で示され、ｍ、ｎは１〜４の整数である。また、Ｒ^１〜Ｒ^４は全て同一でも、異なってもよい。）

(Wherein R ^{1 to} R ⁴ are each represented by H, an alkyl group represented by C _n H _{2n + 1} , or C _n H _2n OH, or C _n H _2n OC _m H _{2m + 1} , m, n Is an integer of ^{1 to 4.} R ^{1 to} R ⁴ may all be the same or different.)

  Metal ions in the treatment liquid have the effect of increasing the denseness of the composite film and improving the corrosion resistance. The metal ions are one or more metals selected from the group consisting of Al, Mg, Mn, Zn, Co, Ti, Sn, Ni, Fe, Zr, Sr, Y, Nb, Cu, Ca, Ba, and Na. It is preferable to add in the form of metal compounds such as oxides, carbonates, phosphates, nitrates, acetates, hydroxides, oxoacid salts, borates and fluorides. More preferred are phosphates, hydroxides, oxides, carbonates, nitrates or acetates. Particularly preferred are one, two or more phosphates, hydroxides, oxides, carbonates, nitrates or acetates selected from Mg ions, Zn ions, Mn ions and Al ions.

  From the viewpoint of improving the corrosion resistance, in particular, a kind selected from the group consisting of Al, Mg, Mn, Zn, Co, Ti, Sn, Ni, Fe, Zr, Sr, Y, Nb, Cu, Ca, Ba, and Na. Or the total amount of two or more kinds added to the treatment liquid is phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin to each treatment liquid. It is preferable that it is 5-20 mass% with respect to the total amount which totaled the addition amount of. More preferably, it is 8-15 mass%. By adding these metal ions, the denseness of the composite film is further improved and high corrosion resistance is obtained. If it is less than 5 mass%, the improvement of the corrosion resistance of the composite film is insufficient, and if it exceeds 20 mass%, precipitates of the composite film may be coarsened, which may deteriorate the corrosion resistance.

In the black zinc-plated steel sheet of the present invention, an organic resin layer is further formed on the surfaces of the black film and the composite film. By forming the organic resin layer, it is possible to improve the processed portion corrosion resistance. The organic resin layer may be formed by applying a paint used for metal pre-coating. Specifically, polyester resin paint, fluororesin paint, vinyl chloride sol paint, acrylic resin paint, and the like are applied. Among these, polyester resin paints frequently used for paints for precoated steel sheets of household electrical appliances having excellent workability are preferable.
In the case of a general precoated steel sheet, the film thickness of the organic resin layer is 10 μm or more, but the film thickness of the organic resin layer in the black zinc-based plated steel sheet of the present invention is 0.1 to 4 μm. Is preferred. Particularly preferred is 0.5 to 2 μm. If it is less than 0.1 μm, the alkali resistance is insufficient, and if it exceeds 4 μm, the conductivity and electromagnetic wave shielding properties may deteriorate.

The organic resin layer of the present invention is obtained by applying the paint on the surface of the composite film by means of roll coating, spray coating, brush coating, dip coating, curtain flow, etc., pressing with a ringer roll, and baking. It is formed.
The baking temperature is preferably about 150 to 200 ° C. as the maximum plate temperature. When the temperature is lower than 150 ° C., the organic resin layer may be slightly insufficiently cured, or the solvent may remain in the organic resin layer, which may be slightly inferior in corrosion resistance. Moreover, when it exceeds 200 degreeC, there is no problem in particular, However, Yellowing by the partial decomposition | disassembly of the component of this organic resin layer may be recognized.

Hereinafter, the present invention will be described in detail based on examples. The present invention is not limited to these examples.
(Examples 1-25, Comparative Examples 1-7)
In Examples 1 to 25 and Comparative Examples 1 to 7, a black coating, a composite coating, and an organic resin layer were formed on a zinc-based plated steel plate by the following method to produce a black zinc-based plated steel plate. Further, as a reference example, an electrogalvanized steel sheet (plating adhesion amount 20 g / m ² ) that was not subjected to blackening treatment and did not form a composite film and an organic resin layer was used.
(Formation of black film)
After applying zinc-nickel alloy plating (plating coverage 20 g / m ² , nickel content 15 mass%) on both sides of a cold rolled steel sheet with a steel strip width of 1200 mm and a steel strip thickness of 0.8 mm in an electroplating line, Anodizing in a solution containing sodium chlorate and sodium sulfate (chlorate ion concentration 80 g / l, sulfate ion concentration 100 g / l, pH 1.0, temperature 50 ° C.) at a current density of 40 A / dm ² with a nickel electrode as the counter electrode And a black film was formed on both sides. The black film thickness was adjusted by controlling the anodizing time. The black film thickness is shown in Tables 1 and 2. The film thickness of the black film was measured by observing a cross-section TEM (transmission electron microscope) of a thin film prepared by FIB (focused ion beam processing apparatus) processing.

(Formation of composite film)
Orthophosphoric acid aqueous solution (using reagent special grade phosphoric acid), sodium vanadate (reagent special grade), itaconic acid (reagent deer special grade), basic zinc carbonate (reagent deer special grade), aluminum hydroxide (reagent deer special grade), manganese hydroxide (Reagent deer first grade), magnesium oxide (reagent special grade), and tetramethylolated glycoluril resin ("Cymel 1172", manufactured by Mitsui Cytec Co., Ltd.) are added in the treatment liquid shown in Tables 1 and 2. Each was added to prepare a treatment liquid (total added amount concentration: 20 mass%). The pH was adjusted to 2.9 using aqueous ammonia (special grade reagent).
As Comparative Example 7, 100.0 parts by mass of a water-soluble acrylic resin (manufactured by Kanto Chemical Co., Ltd., polyacrylic acid) and 2.5 parts by mass of a thiocarbonyl group-containing compound (manufactured by Kanto Chemical Co., Ltd., thiourea) , 1.0 part by mass of a phosphoric acid compound (manufactured by Kanto Chemical Co., Ltd., ammonium phosphate) and 10.0 parts by mass of finely divided silica (Nissan Chemical Industry Co., Ltd., Snowtex-N) in deionized water The coating agent which added and the total addition amount density | concentration became 20 mass% was created.

The treatment liquid is applied to both surfaces of the zinc-nickel alloy plated steel sheet on both surfaces of the black film using a roll coater, and dried so that the maximum plate temperature reaches 120 ° C. in 15 seconds. Formed.
Further, the coating agent of Comparative Example 7 was applied to the surface of the black film on both surfaces of the zinc-nickel alloy plated steel sheet using a bar coater, and heated so that the maximum temperature reached 150 ° C. in 20 seconds. A film was formed.
Of the composite film and the amount of the coating, and phosphate ion, vanadate ion, metal (zinc, aluminum, manganese, magnesium, sodium) ion, α, β unsaturated carboxylic acid and glycoluril resin in the composite film. Addition amounts are shown in Tables 1 and 2. The amount of adhesion was determined in advance by fluorescent X-ray analysis using a calibration curve with a standard sample in which a composite film was formed with a constant phosphoric acid concentration in the treatment solution.

(Formation of organic resin layer)
A polyester-melamine resin-based PCM paint ("V knit # 9900", manufactured by Dainippon Paint Co., Ltd.) is mixed with thinner ("V knit thinner", manufactured by Dainippon Paint Co., Ltd.), and the viscosity is adjusted to Ford Cup # 4- The coating solution obtained by adjusting to 20 s (25 ° C.) was applied to both surfaces of the composite film with a roll coater, and heated so that the maximum plate temperature reached 200 ° C. in 20 seconds to form an organic resin layer. Formed. Tables 1 and 2 show the film thickness of the organic resin. The film thickness was measured by observing a cross section SEM (scanning electron microscope).

About the black zinc-based plated steel sheet obtained by the above method, the adhesion, heat absorption and heat dissipation, corrosion resistance (flat plate portion and bending portion), alkali resistance, conductivity and electromagnetic wave shielding property of the organic resin layer are as follows. evaluated.
(Adhesion test)
A test piece obtained by cutting the black zinc-based plated steel sheet into a size of 100 mm in length and 50 mm in width was bent at 90 ° with an outer R of 1.5 mm to provide a bent portion. After applying an adhesive tape (trade name: cellophane adhesive tape, manufactured by Nichiban Co., Ltd.) along the crease on the outer side of the bent portion, separation is performed to determine whether the composite film and / or the organic resin layer is peeled off. Judgment was made visually by the discoloration of the appearance. The results are shown in Tables 3 and 4, where ◯ indicates no discoloration, Δ indicates a discoloration area ratio of less than 5%, and x indicates a discoloration area ratio of 5% or more. The discolored area ratio here is a percentage of the total area where the composite film and / or the organic resin is peeled and the appearance is discolored with respect to the total area of the bent portion where the adhesive tape is applied.

(Heat absorption and heat dissipation test)
The test apparatus shown in FIG. The housing 1 (inner dimensions: 280 mm long, 280 mm wide, 110 mm high, top surface is completely open) is assembled with an acrylic resin plate (plate thickness 2 mm), and the inner surface (side surface and bottom surface) of the housing 1 is assembled. An aluminum foil 2 (trade name: aluminum foil, manufactured by Takeda Corporation) was applied to completely cover the inner surface (side surface and bottom surface) of the housing 1. Silicon rubber heater 4 (Product name: Silicon rubber heater, manufactured by AS ONE Corp., 150 mm long, 150 mm wide) so as to be located 10 mm above the bottom surface on the aluminum frame 3 installed at the center of the inner bottom surface of the housing 1. The power density was set to 0.6 w / cm ² -100V, and the voltage was supplied from the DC stabilized power supply 5 (maximum 70V, 1A) to generate heat (input 65V × 705mA = 45.8W). A test piece cut out from the black zinc-based plated steel sheet to a size of 300 mm in length and 300 mm in width as the top plate 6 on the housing 1 is coated with the organic resin layer. It was placed in contact with the packing 7 installed on the upper end of the side surface and sealed. An aluminum foil 8 (200 mm long and 200 mm wide) for preventing direct radiation from the heater 4 to the sheathed platinum resistance warmer 10 is placed in the space between the sheathed platinum resistance warming body 10 and the heater 4 below. The aluminum foil 8 was supported on the four corners of the aluminum foil 8 so that the position was maintained directly above the rubber heater 4 and parallel to the bottom surface at a fixed position of 35 mm from the bottom surface.

  A sheathed platinum resistance thermometer 10 (diameter 1.6 mmφ, length 150 mm) is housed inside the housing 1 that is 35 mm vertically downward from the top plate 6 and 40 mm vertically upward from the aluminum foil 8. 1 was inserted so as to be kept horizontal from the side surface of 1, and a temperature in the vicinity of 35 mm could be measured in the center in the horizontal direction inside the housing 1 and vertically downward from the top plate 6. A change in the internal temperature of the housing 1 was recorded in the data logger 11, and the heat absorption / release performance of the top plate was determined from the temperature when the internal temperature of the housing 1 reached a steady state. Judgment criteria are: ○ when the temperature drop is 5 ° C or higher compared to the case where the internal temperature of the housing 1 is 5% or more compared to the case where the electrogalvanized steel sheet shown in the reference example is used for the top plate 6. It was. The determination results are shown in Tables 3 and 4.

  FIG. 2 is a graph showing a change in temperature inside the casing 1 with heating time when the electrogalvanized steel sheet of the reference example and the black zinc-based plated steel sheet of Example 1 are used for the top plate 6. In the latter case, it can be seen that the internal temperature of the housing 1 is lower than that of the former, and the heat absorbing / dissipating property is good.

(Corrosion resistance test)
The black galvanized steel sheet is cut into the same size as in the adhesion test, and a test piece provided with a bent portion is similarly provided with a cycle salt spray test (salt water in accordance with JIS Z 2371-2000 neutral salt spray test). Repeated test of spraying for 8 hours for spraying and 1 hour for spraying stop 16h) 3 cycles), bending part and flat part which is not bent and is coated with the organic resin layer The occurrence of white rust was determined visually. The case where no white rust was generated was indicated by ◯, the case where the white rust generation area ratio was less than 5% was indicated by Δ, and the case where the white rust generation area ratio was 5% or more was indicated by x. The determination results are shown in Tables 3 and 4. The white rust generation area ratio here is a percentage of the total white rust area with respect to the total area where the bent portion and the flat plate portion are observed.

(Alkali resistance test)
A test piece cut into a size of 100 mm in length and 50 mm in width from the black zinc-based plated steel sheet was immersed in 2 g / l of a degreasing solution (“Pulclean N364S”, manufactured by Nihon Parkerizing Co., Ltd.) at 60 ° C. for 2 min. The peeling of the composite film and / or the organic resin layer immediately after removal was visually determined by discoloration of the appearance. The results are shown in Tables 3 and 4, where ◯ indicates no discoloration, Δ indicates a discoloration area ratio of less than 5%, and x indicates a discoloration area ratio of 5% or more. The discoloration area ratio here is a percentage of the total discoloration area with respect to the total observation area.

(Conductivity test)
Using a surface electrical resistance meter ("Loresta GP", manufactured by Mitsubishi Chemical Corporation) with a 4-probe ESP probe at a load of 240 g / probe, the black zinc-plated steel sheet is 200 mm long and 100 mm wide. The electrical resistance of the surface of the cut out test piece on which the organic resin layer was applied was measured at 10 locations. Arrangement of 10 places is arbitrary 5 places where the vertical position is mainly different in the area of 200 mm length and 50 mm width of the half of the test piece, and arbitrarily where the vertical position is also different in the other half area similarly. Five locations were provided.
The case where the resistance value was less than 1 mΩ at all 10 locations was evaluated as “◯”, the case where there were 1 to 2 locations where the resistance value was 1 mΩ or more was Δ, and the case where there were 3 locations where the resistance value was 1 mΩ or more was determined as “X”. The determination results are shown in Tables 3 and 4.

(Electromagnetic wave shielding test)
The electromagnetic wave shielding property of the present invention was evaluated by measuring leakage noise as shown in FIG.
A 20 MHz clock 24 was placed as an oscillation source in an Al casing 23 having an outer shape of 100 mm × 100 mm × 100 mm molded from an aluminum plate having a thickness of 2 mm, and a high frequency of 20 to 1000 MHz was output every 20 MHz.
The upper surface of the Al housing 23 has an opening of 100 mm × 100 mm, a 20 mm edge 25 is projected on the side surface, and the upper surface of the Al housing that comes into contact with the evaluation surface of the sample has an outer shape of 140 mm × 140 mm and a width of 20 mm. I tried to make it like a picture frame. The evaluation surface 22 of the sample 21 (plate thickness of about 0.8 mm) cut out to a size of 140 mm × 140 mm from the black zinc-based plated steel plate was placed in contact with the upper surface of the Al casing 23 as the lower surface. A load of 1 kg is applied to the sample 21 vertically downward. Here, the evaluation surface 22 is one surface of the sample 21.
Thus, the electromagnetic wave leaking from the frame-shaped joint where the aluminum casing 23 and the sample 21 are in contact is received by the loop antenna 26 with a diameter of 30 mm at a position of 50 mm from the edge 25 and a 25 dB preamplifier. After amplification at 27, analysis was performed using a spectrum analyzer (R3162 from Advantest Corporation) 28.

For the electromagnetic wave shielding properties, the leakage noise on the evaluation surface of the sample was measured with a spectrum analyzer using the apparatus shown in FIG. 3, and charts as shown in FIGS. 4 to 6 were obtained.
In the evaluation of the examples and comparative examples, a peak value having a difference of 3 dB or more from the background was read every 20 MHz from a frequency of 20 MHz to 1000 MHz, and a value converted by the following formula 1 was defined as a noise evaluation value (I).
I = 10 log (10 ^{0.1 d1} +10 ^{0.1 d2} +... +10 ^{0.1 dn} ).
n: number of peaks whose peak value is 3 dB or more different from the background d1, d2,... dn: difference between the peak value and the background (limited to those having 3 dB or more)
As an evaluation standard, the electroplating tinplate (tin plating adhesion amount 2.8 g / m ² ), which is considered to be the most suitable for applications requiring high electromagnetic shielding properties at present, is a practical material. FIG. 5 shows an example of measurement when a sample is used, FIG. 6 shows an example of measurement of Example 1, and FIG. 4 shows an example of measurement without a sample. FIG. 7 shows an example of measurement without a sample without oscillation output of a high frequency. FIG. 7 shows external noise. The difference between the peak value read from FIG. 5 and FIG. 6 and the background (28 dB, indicated by the arrow in FIGS. 4 to 7) (only if it was 3 dB or more) is read and substituted into the above equation 1 to calculate the results were as I ₀ and I. In addition, since the peak of the place which attached | subjected x in FIG. 5, FIG. 6 originates in the external noise shown in FIG.
The test materials of Examples and Comparative Examples, were measured respectively leakage noise, and ○ an _{I / I 0 ≦ 1.2, 1.2} < a _I / I ₀ ≦ 1.4 △ and, I _{/ I} 0> 1.4 was evaluated as x and shown in Tables 3 and 4.

Examples 1 to 25 are all excellent in adhesion, heat-absorbing and heat-absorbing properties, flat plate corrosion resistance, bent portion corrosion resistance, alkali resistance, conductivity, and electromagnetic wave shielding properties. On the other hand, Comparative Example 1 having no black film is inferior in heat absorbing and radiating properties, Comparative Example 2 having no organic resin layer is inferior in bending portion corrosion resistance and alkali resistance, and Comparative Example 3 and Comparative Example 6 having no composite film. Is inferior in adhesion, plate portion corrosion resistance, bending portion corrosion resistance, and alkali resistance. In particular, Comparative Example 6 having a thick organic resin layer of 10.0 μm is further inferior in conductivity and electromagnetic shielding properties.
Further, Comparative Example 4 which does not use the treatment solution to which vanadic acid is added is inferior in flat plate portion corrosion resistance and bending portion corrosion resistance, and Comparative Example 5 which does not use glycoluril resin is adhesiveness, bending portion corrosion resistance and alkali resistance. Is inferior. Comparative Example 7 using a coating agent composed of a water-soluble acrylic resin, a thiocarbonyl group-containing compound, a phosphoric acid compound, and finely divided silica is inferior in adhesion, bending portion corrosion resistance, alkali resistance, conductivity, and electromagnetic wave shielding properties.

FIG. 1 is a schematic diagram of a heat absorption / dissipation test apparatus. FIG. 2 is a diagram showing heat absorption and dissipation when the electrogalvanized steel sheet of Reference Example and the black galvanized steel sheet having the composite film and organic resin layer of Example 1 are used. FIG. 3 is a block diagram for measuring leakage noise of a flat electromagnetic shielding material. FIG. 4 is an example of noise measured in an open state without placing a sample on the Al casing of the apparatus shown in FIG. FIG. 5 is a measurement example of an electromagnetic wave shielding test when an electroplating tin which is a practical material is used as a sample. FIG. 6 is a measurement example of the electromagnetic wave shielding test of Example 1. FIG. 7 shows an example in which external noise was measured without placing a test material on the Al casing of the apparatus shown in FIG. 3, in an open state, and without oscillating and outputting a high frequency.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Case 2 Aluminum foil 3 Base 4 Rubber heater 5 DC stabilized power supply 6 Top plate 7 Packing 8 Radiation prevention aluminum foil 10 Platinum resistance thermometer 11 Data logger 21 Sample 22 Evaluation surface 23 Al case 24 20 MHz clock 25 Edge 26 Loop antenna 27 Preamplifier 28 Spectrum analyzer

Claims (4)

A composite formed by applying a treatment solution containing phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin to the surface of the galvanized steel sheet that has been blackened and dried. A black galvanized steel sheet having a coating and further comprising an organic resin layer formed by applying and baking an organic resin coating on the surface of the composite coating. The black zinc-based plated steel sheet according to claim 1, wherein the metal ions are one or more selected from the group consisting of Mg ions, Zn ions, Mn ions, and Al ions. The content of α, β-unsaturated carboxylic acid in the treatment liquid is 2 to 60 mass% of the total amount of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin. The black zinc-based plated steel sheet according to claim 1 or 2, characterized in that The α, β-unsaturated carboxylic acid is one or more selected from the group consisting of acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid and fumaric acid. The black zinc-plated steel plate in any one of 1-3.

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