JP2004250787A - Black galvanized steel sheet - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a black galvanized steel sheet which has superior heat absorbing/radiating properties, conductivity and corrosion resistance in a formed part, and contains no hexavalent chromium. <P>SOLUTION: The black galvanized steel sheet comprises a blackening-treated galvanized steel sheet; a composite film formed on the surface by applying a treatment liquid containing phosphate ions, vanadate ions, metal ions, an α, β-unsaturated carboxylic acid and a glycoluril resin; and further an organic resin layer formed on the surface of the composite film. <P>COPYRIGHT: (C)2004,JPO&NCIPI

Description

  The present invention relates to a black zinc-plated steel sheet, and more particularly, to a housing material of an electronic device that has excellent heat absorption and radiation properties, conductivity, electromagnetic wave shielding properties, corrosion resistance of a flat plate portion and corrosion resistance of a processed portion, and generates heat when used. The present invention relates to a black zinc-coated 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) and the like has tended to increase, and dissipation of the heat has become a major issue. For example, in the case of a personal computer, especially a desktop personal computer, a fan is generally used for heat radiation, but there is a problem that increasing the number of revolutions and increasing the air flow increases noise. In addition, there are some devices, such as inside car audio, where it is difficult to install a fan. In such a case, if the amount of heat transfer due to heat dissipation from the housing can be increased, the heat generated inside the device can be quickly dissipated to the outside of the device without a fan or without increasing the rotation speed of the fan. Can be.

  In view of the above, attempts have been made to impart heat absorption and radiation properties to steel sheets. 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 wavelength range of infrared rays, at which the thermal emissivity of each pigment component is maximized, is different.By combining these pigments, a coating film that exhibits a high thermal emissivity over a wide wavelength range can be applied to the steel sheet surface. It is an invention formed in. When such a steel plate is used as a casing material, heat generated from inside the device can be effectively released to the outside through the casing.

  However, in order to obtain a sufficient effect, it is necessary to contain a large amount of the pigment, and therefore, the film thickness must be increased, which causes a problem of high cost. There is also a problem that the electric 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 reliably ground the housing, and for that purpose, it is important that the surface of the steel sheet has good conductivity. Since prevention of leakage of electromagnetic waves is indispensable for electronic devices, there is a limit to the use of a paint containing a large amount of a pigment having a high thermal emissivity in order to impart heat absorption and radiation properties.

  On the other hand, black zinc-coated steel sheets conventionally used for internal parts of copying machines, etc., have a black appearance and, in addition to the characteristic of low reflectance to visible light, are higher than ordinary zinc-coated steel sheets. It is known to have a thermal emissivity.

By the way, a method for forming a black film on a steel sheet is generally roughly classified as follows.
(A) a method of applying a paint containing a black pigment such as carbon black by a spray or a roll coater to form a black film having a 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 sheet according to 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 sheet.
There are various methods classified into the method (b), and in recent years, from the viewpoint of environmental protection, a method of forming a black film containing no hexavalent chromium has attracted attention. For example, a metal / oxide composite black coating containing nickel and zinc metal, nickel and zinc oxide, and optionally a hydroxide is formed on the surface of a zinc-based plating layer using a zinc-based plated steel sheet as a base material. Further, a non-chrome type rust preventive coating layer containing a resin and 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 thereon, Thus, a weldable non-chrome type black-treated galvanized steel sheet having an organic resin layer optionally containing a black pigment and / or a rust-preventive pigment as an upper layer has been proposed (for example, Patent Document 2).

In addition, 30 to 200 mg / m ^{2 of} one or more metals selected from the group consisting of Ni, Co, and Fe are substituted and deposited on a metal substrate having Zn on the surface, and an oxide layer of these metals is formed. There has been proposed a surface-treated metal material having an excellent black appearance, characterized by the formation of (for example, Patent Document 3).

  The purpose of the black steel sheet according to the method (b) is to provide a black zinc-plated steel sheet which has been subjected to a corrosion resistance treatment instead of a chromate treatment. There was a problem that corrosion resistance was insufficient.

JP-A-2002-226873 JP-A-2000-290783 JP-A-2002-47579

  The present invention has been made in view of such circumstances, and is economical, has excellent heat absorption and radiation properties, is excellent in conductivity, electromagnetic wave shielding properties and flat plate corrosion resistance, and also has excellent corrosion resistance in a machined portion, and generates heat inside. It is an object of the present invention to provide a black zinc-plated steel sheet that can be used without painting and that does not contain hexavalent chromium, as a housing material of an electronic device.

  The present invention is formed by applying a treatment liquid containing a phosphate ion, a vanadate ion, a metal ion, an α, β-unsaturated carboxylic acid and a glycoluril resin to a surface of a blackened galvanized steel sheet. A black zinc-plated steel sheet comprising: a composite film provided with an organic resin layer on the surface of the composite film.

  According to the present invention, it is possible to obtain a black zinc-coated steel sheet which does not contain any chromium and is excellent in heat absorbing and dissipating properties, conductivity, electromagnetic wave shielding properties, corrosion resistance in a plane portion, and corrosion resistance in a processed portion.

The black zinc-coated steel sheet of the present invention has a surface in which the blackening-treated zinc-coated steel sheet has a phosphate ion (PO ₄ ³⁻ ), a vanadate ion (VO ₃ ⁻ ), a metal ion, α, β-unsaturated. It has a composite film formed by applying a treatment liquid to which a carboxylic acid and a glycoluril resin have been added, and further has an organic resin layer on the surface of the composite film, so that heat absorption and radiation properties, conductivity, and electromagnetic wave shielding can be achieved. In addition to being excellent in corrosion resistance, in addition to the flat plate portion corrosion resistance, it is also excellent in the 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 serving as the base material of the present invention is a galvanized steel sheet or a zinc alloy-coated steel sheet, for example, a hot-dip galvanized steel sheet, a zinc-aluminum (Zn-5 mass% Al) hot-dip coated steel sheet, a zinc-coated steel sheet. A zinc-coated steel sheet such as an aluminum (Zn-55 mass% Al) hot-dip coated steel sheet is blackened. In particular, a blackened zinc-nickel alloy-based plated steel sheet is preferable because the black film formed by the blackening treatment has excellent adhesion and the mass production quality is stable. The blackening treatment is preferably performed after subjecting the zinc-based plated steel sheet to ordinary treatment such as hot water washing and alkali degreasing.

  First, the surface of the zinc-based plated layer of the zinc-based plated steel sheet which is the base material of the present invention is blackened to form a black film. The thickness of the black film is preferably from 0.01 to 0.5 μm, and particularly preferably from 0.05 to 0.2 μm. When the thickness is less than 0.01 μm, not only blackening is insufficient, but also sufficient heat absorbing / radiating properties may not be obtained. If it exceeds 0.5 μm, the adhesion of the black film to the galvanized steel sheet may deteriorate. The thickness of the black film can be confirmed by cross-sectional TEM (transmission electron microscope) observation of a thin film formed by FIB (focused ion beam processing device) processing or the like.

  The blackening method is not particularly limited, and may be an electrochemical treatment method such as anodic electrolysis, cathodic treatment, or alternating electrolysis, or a treatment method in which a metal such as nickel, cobalt, or iron is replaced and precipitated with an oxide of the metal. General method can be used. By these methods, a black coating mainly composed of an oxide is formed, so that the surface of the zinc-based plated steel sheet can be blackened.

From the viewpoint of the stability, the blackening treatment method uses an electric zinc-nickel alloy-plated steel sheet having a zinc-nickel alloy layer, for example, a chlorate ion (ClO ₃ ⁻ ) of 5 to 100 g / l and a sulfate ion (SO _4). ^It is recommended to perform anodic electrolysis in an aqueous solution containing 10 to 300 g / l of ^2- ) under the conditions of pH 0.5 or more and less than 3.0, a temperature of 30 to 75 ° C., and an amount of electricity of 10 to 300 C / dm ² . The black film formed on the surface of the galvanized steel sheet contains at least metals containing zinc and oxides of these metals, and may further contain hydroxides of these metals. Examples of these metals include zinc and nickel.

The composite coating of the present invention is applied to a surface of a blackened galvanized steel sheet with a treatment liquid containing a phosphate ion, a vanadate ion, a metal ion, an α, β-unsaturated carboxylic acid and a glycoluril resin. For example, a treatment solution in which a vanadate compound, a metal compound, an α, β-unsaturated carboxylic acid and a glycoluril resin are added to a phosphoric acid aqueous solution is coated with a blackened zinc-coated steel sheet surface. And dried.
From the viewpoint of ease of application and drying of the treatment liquid, all addition of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin of the treatment liquid It is preferable that the concentration is 10 to 30 mass%. As the solvent, water or a mixed medium with an organic solvent or an inorganic solvent miscible with water is used.
Since the treatment liquid is acidic due to the addition of phosphate ions, application of the treatment liquid partially elutes zinc from the zinc-based plating layer and increases the zinc ion activity in the treatment liquid. During the subsequent drying, various components in the treatment solution 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 removed. A containing composite film is formed.

  The pH of the treatment liquid is preferably 1.5 to 4, and 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 dissolve violently between application and drying of the treatment liquid, and the zinc-based plating and the black film may be damaged. When the pH exceeds 4, various metal ions added to the treatment liquid cannot be stably present, and may precipitate as hydroxides, making application difficult. The treatment liquid is applied by a usual method, for example, a roll coater method, a spray method, a bar coater method or the like.

  The drying after the application of the treatment liquid is preferably performed at a maximum ultimate plate temperature of 80 to 250 ° C. More preferably, it is 100 to 180 ° C. If the temperature is lower than 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 wastes energy.

The amount of adhesion of the composite coating of the present invention is preferably from 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 electric resistance increases, and the necessary conductivity and electromagnetic wave shielding properties may not be obtained.

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

The vanadate ions in the treatment liquid have an effect of improving the corrosion resistance of the composite coating. 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 Is preferably 0.5 to 20 mass% with respect to the total amount of More preferably, it is 4 to 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. In addition, this means that the vanadate ion concentration in the processing solution is increased, and becomes unstable in the processing solution, which may cause a precipitate to be generated during storage of the processing solution. . The vanadic acid is preferably added to the treatment liquid in the form of a vanadate such as sodium vanadate, potassium vanadate, ammonium vanadate and the like.

  The α, β-unsaturated carboxylic acid in the treatment liquid has an effect of improving the adhesion of the composite coating to the black coating. The amount of the α, β-unsaturated carboxylic acid added to the treatment liquid is determined by the amount of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin added to the treatment liquid. It is preferably 2 to 60 mass% based on the total amount of the additions. More preferably, it is 10 to 30 mass%. If it is less than 2 mass%, the effect of improving the adhesion to the black film is insufficient, and as a result, the corrosion resistance of the processed portion may be insufficient. If it exceeds 60 mass%, the conductivity and the electromagnetic wave shielding property 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 adhesiveness to an organic resin layer provided on the surface of the composite film, for example, a polyester resin layer, which will be described later. The amount of glycoluril resin added to the treatment liquid was the sum of the amounts of phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin added to the treatment liquid. 1-20 mass% is preferable with respect to the total amount. More preferably, it is 5 to 15 mass%. If it is less than 1 mass%, the effect of improving the adhesion to the organic resin layer is insufficient, and as a result, the corrosion resistance of the processed portion may be insufficient. If it exceeds 20 mass%, the conductivity and the electromagnetic wave shielding property may deteriorate.

The glycoluril resin is a monomer represented by the following structural formula, or a polymer of the monomer, or 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 a derivative in which methylol, butyrol, or the like is added to all or a part of the 1-, 3-, 4-, 6-amino groups of glycoluril, and the derivative is further methylated, methyl / ethylated, or butylated. And alkyl etherified derivatives.
Examples of the condensate of the monomer include an oligomer obtained by condensation via a methylol group or the like.
Preferred are tetramethylolated glycoluril and its oligomers, which have excellent water solubility and 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 or 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} , and m, n Is an integer of ^{1 to 4. Further} , all of R ^{1 to} R ⁴ may be the same or different.)

  The metal ions in the treatment liquid have the effect of increasing the denseness of the composite coating and improving the corrosion resistance. The metal ion is 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 Is preferably added in the form of metal compounds such as oxides, carbonates, phosphates, nitrates, acetates, hydroxides, oxoates, 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 corrosion resistance, in particular, Al, Mg, Mn, Zn, Co, Ti, Sn, Ni, Fe, Zr, Sr, Y, Nb, Cu, Ca, Ba, and a kind selected from the group consisting of Na , Or a total amount of two or more kinds thereof to the treatment liquid is such that phosphate ion, vanadate ion, metal ion, α, β-unsaturated carboxylic acid and glycoluril resin are added to the respective treatment liquid. Is preferably 5 to 20% by mass based on the total amount of the components added. More preferably, it is 8 to 15 mass%. By adding these metal ions, the denseness of the composite film is further improved, and high corrosion resistance is obtained. If the amount is less than 5 mass%, the corrosion resistance of the composite film is insufficiently improved, and if the amount exceeds 20 mass%, the precipitates of the composite film become coarse, which may impair the corrosion resistance.

In the black zinc-plated steel sheet of the present invention, an organic resin layer is further formed on the surface of the black film and the composite film. By forming the organic resin layer, the corrosion resistance of the processed portion can be improved. The organic resin layer may be formed by applying a paint used for precoating a metal. Specifically, a polyester resin paint, a fluororesin paint, a vinyl chloride sol paint, an acrylic resin paint, or the like is applied. Among them, a polyester resin paint which is frequently used as a paint for a pre-coated steel sheet of a home appliance having excellent workability is preferable.
In the case of a general pre-coated steel sheet, the thickness of the organic resin layer is 10 μm or more, but the thickness of the organic resin layer in the black zinc-plated steel sheet of the present invention is 0.1 to 4 μm. Is preferred. Particularly preferred is 0.5 to 2 μm. When the thickness is less than 0.1 μm, the alkali resistance is insufficient, and when it exceeds 4 μm, the conductivity and the electromagnetic wave shielding property may be deteriorated.

The organic resin layer of the present invention, on the surface of the composite coating, the paint is applied by means such as roll coating, spray coating, brush coating, dip coating, curtain flow, pressed with a ringer roll, and baked. It is formed.
The baking temperature is preferably set to about 150 to 200 ° C. as the maximum attained sheet temperature. When the temperature is lower than 150 ° C., the curing of the organic resin layer is slightly insufficient, or the solvent remains in the organic resin layer, so that the corrosion resistance may be slightly deteriorated. When the temperature exceeds 200 ° C., there is no particular problem, but yellowing due to partial decomposition of the components of the organic resin layer may be observed.

Hereinafter, the present invention will be described in detail with reference to examples. The present invention is not limited to these examples.
(Examples 1 to 25, Comparative Examples 1 to 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-coated steel sheet by the following method to produce a black zinc-coated steel sheet. As a reference example, an electrogalvanized steel sheet (plating adhesion amount: 20 g / m ² ) which was not subjected to blackening treatment and did not form a composite film and an organic resin layer was used.
(Formation of black film)
In the electroplating line, both sides of a cold-rolled steel sheet having a steel strip width of 1200 mm and a steel strip thickness of 0.8 mm are subjected to zinc-nickel alloy plating (coating weight 20 g / m ² , nickel content 15 mass%), 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.), anodize at a current density of 40 A / dm ² with a nickel electrode as a counter electrode. And a black film was formed on both sides. The thickness of the black film was adjusted by controlling the anodizing time. The thickness of the black film is shown in Tables 1 and 2. The black film thickness was measured by observing a cross-sectional TEM (transmission electron microscope) of a thin film formed by FIB (focused ion beam processing device) processing.

(Formation of composite film)
Orthophosphoric acid aqueous solution (using reagent grade phosphate), sodium vanadate (reagent grade), itaconic acid (reagent grade), basic zinc carbonate (reagent grade), aluminum hydroxide (reagent grade), manganese hydroxide (Reagent Kana grade), magnesium oxide (special grade reagent), and tetramethylolated glycoluril resin ("Cymel 1172", manufactured by Mitsui Cytec Co., Ltd.) so that the amounts added in the processing solutions shown in Tables 1 and 2 Were added to each other to prepare a treatment solution (total addition amount concentration: 20 mass%). The pH was adjusted to 2.9 using aqueous ammonia (reagent deer special grade).
Further, 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 parts 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 Industries, Ltd., Snowtex-N) in deionized water. A coating agent having a total concentration of 20 mass% was prepared.

The treatment liquid was applied to both surfaces of the zinc-nickel alloy-plated steel sheet on both surfaces using a roll coater on the surface of the black film, and dried so that the maximum temperature reached 120 ° C. in 15 seconds to form a composite film. 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.
The amount of the composite film and the amount of the coating film, and the amount of phosphate ion, vanadate ion, metal (zinc, aluminum, manganese, magnesium, sodium) ion, α, β unsaturated carboxylic acid and glycoluril resin in the composite film The addition amounts are shown in Tables 1 and 2. The attached amount was determined by a fluorescent X-ray analysis using a calibration curve with a standard sample having a composite film formed with the concentration of phosphoric acid in the treatment solution being fixed in advance.

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

Regarding the black zinc-plated steel sheet obtained by the above method, the adhesion, heat absorption and radiation properties, corrosion resistance (flat portion and bent portion), alkali resistance, conductivity and electromagnetic wave shielding property of the organic resin layer are determined by the following methods. evaluated.
(Adhesion test)
A test piece cut out of the black zinc-plated steel sheet into a size of 100 mm in length and 50 mm in width was bent at an outer radius of 1.5 mm by 90 ° to provide a bent portion. An adhesive tape (trade name: cellophane adhesive tape, manufactured by Nichiban Co., Ltd.) was applied along the outer crease of the bent portion and then separated to determine whether or not the composite film and / or the organic resin layer had peeled. It was judged 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 × indicates a discoloration area ratio of 5% or more. The discoloration area ratio as used herein is the percentage of the total area of the composite coating and / or the organic resin peeled off and discolored in appearance with respect to the entire area of the bent portion to which the adhesive tape was applied.

(Test of heat absorption and radiation)
The test device shown in FIG. 1 was prepared, and a heat absorption / radiation test was performed. The housing 1 (inner dimensions: 280 mm in height, 280 mm in width, 110 mm in height, and the upper surface is completely open) is assembled with an acrylic resin plate (2 mm in thickness), and attached to the inner surface (side surface and bottom surface) of the housing 1. An aluminum foil 2 (trade name: aluminum foil, manufactured by Takeda Corporation) was attached to completely cover the inner surface (side surface and bottom surface) of the housing 1. Silicon rubber heater 4 (trade name: Silicon Rubber Heater, manufactured by AS ONE Corporation, 150 mm in height, 150 mm in width) so that it is located at a height of 10 mm from the bottom on an aluminum base 3 installed in the center of the bottom inside of the housing 1. , And a power density of 0.6 w / cm ² -100 V pressurized), and a voltage was supplied from a stabilized DC power supply 5 (maximum 70 V, 1 A) to generate heat (input 65 V × 705 mA = 45.8 W). As the top plate 6 of the case 1, a test piece cut out from the black zinc-plated steel sheet into a size of 300 mm in length and 300 mm in width is coated with the organic resin layer. It was placed so as to be in contact with the packing 7 installed at the upper end of the side surface) and sealed. An aluminum foil 8 (200 mm long, 200 mm wide) for preventing direct radiation from the heater 4 to the sheath-type platinum resistance heater 10 was placed in a space between the sheath-type platinum resistance heater 10 and the heater 4 as shown below. The aluminum foil 8 was supported by wires 9 at a fixed position just above the rubber heater 4 and at a fixed position of 35 mm from the bottom surface, in parallel with the bottom surface, so that the position could be maintained.

  A sheath-type platinum resistance thermometer 10 (diameter 1.6 mmφ, length 150 mm) is placed inside the casing 1 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 horizontal, so that a temperature around 35 mm could be measured in the horizontal center of the housing 1 and vertically downward from the top plate 6. The change in the internal temperature of the housing 1 was recorded on the data logger 11, and the heat absorption / dissipation property of the top plate was determined from the temperature when the internal temperature of the housing 1 reached a steady state. The criterion is as follows: when the internal temperature of the housing 1 is 5 ° C. or more compared with the case where the electro-galvanized steel sheet shown in Reference Example is used for the top plate 6, × And The determination results are shown in Tables 3 and 4.

  FIG. 2 is a graph showing a change in temperature inside the housing 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, the internal temperature of the housing 1 is lower than that of the former, and it can be seen that the heat absorbing and radiating property is good.

(Corrosion resistance test)
The black zinc-coated steel sheet was cut into the same size as that in the adhesion test, and a test piece provided with a bent portion was similarly subjected to a cycle salt water spray test (JIS Z 2371-2000 salt water according to a neutral salt water spray test). (Repetition test of a test in which spraying is performed for 8 hours and spraying is stopped for 16 hours as one cycle) is performed for 3 cycles, and a bent portion and a flat portion which is a non-bent flat surface on which the organic resin layer is applied. And each white rust occurrence was visually determined.が な い indicates that no white rust was generated, Δ indicates that the white rust generation area ratio was less than 5%, and X indicates that the white rust generation area ratio was 5% or more. The determination results are shown in Tables 3 and 4. Here, the white rust occurrence area ratio is a percentage of the sum of the white rust area with respect to the entire area of each of the bent portion and the flat portion.

(Alkali resistance test)
A test piece cut out from the black zinc-plated steel sheet to a size of 100 mm in length and 50 mm in width was immersed in 2 g / l of a degreasing solution (“Palclean N364S”, manufactured by Nippon Parkerizing Co., Ltd.) at 60 ° C. for 2 minutes, The peeling of the composite film and / or the organic resin layer immediately after the removal was visually judged 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 × indicates a discoloration area ratio of 5% or more. Here, the discoloration area ratio is a percentage of the total discoloration area with respect to the entire observation area.

(Conductivity test)
Using a surface electric resistance meter ("Loresta GP", manufactured by Mitsubishi Chemical Corporation), the four-point ESP probe was used to convert the black zinc-plated steel sheet to a size of 200 mm in length and 100 mm in width at a load of 240 g / tip. The electrical resistance of the surface of the cut test piece to which the organic resin layer was applied was measured at 10 points. Arrangement of 10 places is as follows. Half of the test piece has an arbitrary length of 200 mm and a width of 50 mm, and has an arbitrary position mainly different in the vertical direction in the other half area. There were five places.
In each of the ten places, the case where the resistance value was less than 1 mΩ was evaluated as ○, the case where the resistance value was 1 mΩ or more was one or two places, and the case where the resistance value was 3 mΩ or more was evaluated as ×. 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 housing 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, and a 20 mm edge 25 protrudes from the side surface, and the upper surface of the Al housing in contact with the evaluation surface of the sample has an outer shape of 140 mm × 140 mm and a width of 20 mm. It was framed. A sample 21 (plate thickness of about 0.8 mm) cut out from the black zinc-plated steel sheet into a size of 140 mm × 140 mm was placed in contact with an upper surface of an Al casing 23 with an evaluation surface 22 as a lower surface. Then, 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.
The electromagnetic wave leaking from the frame-shaped joint where the Al casing 23 and the sample 21 are in contact with each other is received by the loop antenna 26 having a diameter of 30 mm at a position 50 mm from the edge 25 and a 25 dB preamplifier is provided. After amplification at 27, analysis was performed using a spectrum analyzer (R3162 manufactured by Advantest Co., Ltd.).

The electromagnetic wave shielding property was obtained by measuring the leakage noise on the evaluation surface of the sample with a spectrum analyzer using the apparatus shown in FIG. 3 and obtaining charts as shown in FIGS.
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 equation 1 was used as a noise evaluation value (I).
I = 10 log (10 ^0.1d1 +10 ^0.1d2 +... +10 ^0.1dn ) Expression 1
n: number of peaks whose peak value differs from the background by 3 dB or more d1, d2,... dn: difference between the peak value and the background (limited to those having a value of 3 dB or more)
As an evaluation criterion, electroplating tin (amount of tin plating: 2.8 g / m ² ), which is considered to be the most suitable for applications requiring high electromagnetic wave shielding properties at present, is a practical material. FIG. 5 shows a measurement example in the case of a sample, FIG. 6 shows a measurement example of Example 1, and FIG. 4 shows an example of measurement in a state without a sample. FIG. 7 shows an example in which measurement was performed without a sample without oscillating high-frequency output. FIG. 7 shows external noise. The difference between the peak value read from FIGS. 5 and 6 and the background (28 dB; indicated by arrows in FIGS. 4 to 7) (limited to those which are equal to or more than 3 dB) is read and substituted into Equation 1 above to calculate. The results were defined as I ₀ and I. Note that the peaks indicated by the crosses in FIGS. 5 and 6 are derived from the external noise shown in FIG.
Leakage noise was measured for each of the test materials of Examples and Comparative Examples, and I / I ₀ ≦ 1.2 was evaluated as “○”, 1.2 <I / I ₀ ≦ 1.4 as Δ, and I / I ₀ > 1.4 was evaluated as x and shown in Tables 3 and 4.

All of Examples 1 to 25 are excellent in adhesion, heat absorption and radiation, 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 dissipating properties, and Comparative Example 2 having no organic resin layer is inferior in corrosion resistance and alkali resistance in a bent portion, and Comparative Examples 3 and 6 having no composite film. Comparative Example 6 is inferior in adhesion, flat plate corrosion resistance, bent section corrosion resistance, and alkali resistance. In particular, Comparative Example 6 in which the organic resin layer is as thick as 10.0 μm is further inferior in conductivity and electromagnetic wave shielding properties.
Further, Comparative Example 4 which did not use the treatment liquid to which vanadic acid was added was inferior in the corrosion resistance of the flat plate portion and the corrosion resistance of the bent portion, and Comparative Example 5 which did not use the glycoluril resin had adhesion, corrosion resistance and the alkali resistance of the bent portion. Is inferior. Comparative Example 7, which used a coating agent composed of a water-soluble acrylic resin, a thiocarbonyl group-containing compound, a phosphoric acid compound, and finely divided silica, was inferior in adhesion, bending section corrosion resistance, alkali resistance, conductivity, and electromagnetic wave shielding properties.

FIG. 1 is a schematic view of a heat absorption / release test apparatus. FIG. 2 is a diagram illustrating heat absorption and radiation properties when an electrogalvanized steel sheet of a reference example and a black zinc-coated steel sheet having a composite film and an organic resin layer of Example 1 are used. FIG. 3 shows a block diagram for measuring leakage noise of a flat electromagnetic wave 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 shows a measurement example of an electromagnetic wave shielding property test in which a tinplate of electroplating, which is a practically used material, is used as a sample. FIG. 6 is a measurement example of the electromagnetic wave shielding test of the first embodiment. FIG. 7 shows an example in which an external noise is measured in an open state and without oscillating high-frequency output without placing the test material on the Al casing of the apparatus shown in FIG.

Explanation of reference numerals

REFERENCE SIGNS LIST 1 housing 2 aluminum foil 3 mount 4 rubber heater 5 DC stabilized power supply 6 top plate 7 packing 8 radiation preventing aluminum foil 10 platinum resistance temperature detector 11 data logger 21 sample 22 evaluation surface 23 aluminum housing 24 20 MHz clock 25 Border 26 Loop antenna 27 Preamplifier 28 Spectrum analyzer

Claims (1)

  A composite film formed by applying a treatment liquid containing a phosphate ion, a vanadate ion, a metal ion, an α, β-unsaturated carboxylic acid and a glycoluril resin to a surface of a blackened galvanized steel sheet. And further comprising an organic resin layer on the surface of the composite coating.

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