JP6750432B2 - Organic resin coated steel sheet - Google Patents

Description

TECHNICAL FIELD The present invention relates to an organic resin-coated plated steel sheet, more specifically, an organic resin that can be used as a material for home appliances, building materials, civil engineering, machinery, automobiles, furniture, etc. without further coating after press molding. The present invention relates to a coated plated steel sheet. The organic resin-coated plated steel sheet of the present invention is particularly excellent in PM (pressure mark) resistance and scratch resistance.

For home appliances, building materials, automobiles, etc., instead of post-painted products that have been painted after conventional molding processing, organic resin coated plated steel sheet (also called pre-coated steel sheet) in which the surface of zinc-based plated steel sheet is coated with an organic resin film ) Has come to be used. After being pressed, the organic resin-coated plated steel sheet is often used as a material for home appliances, building materials, automobiles, etc. without further coating. Therefore, such an organic resin-coated plated steel sheet is required to have excellent scratch resistance so as not to lose its beauty during processing.

For example, Patent Document 1 discloses an organic coating in which beads are included in an organic coating and the particle diameter and glass transition point of the beads are specified, whereby coating damage due to press working is less likely to occur, that is, scratch resistance is excellent. A zinc-based plated steel sheet is disclosed.

Further, Patent Document 2 discloses a precoated metal plate for a drive case of an optical disc or the like, which is excellent in scratch resistance against the optical disc and has conductivity. Specifically, in Patent Document 2, conductivity is secured by limiting the film thickness of the resin coating, and beads are included in the resin coating to secure scratch resistance.

Patent Document 3 also discloses a pre-coated metal plate containing beads as a pre-coated metal plate with improved scratch resistance against an optical disc. In Patent Document 3, the average particle diameter and addition amount of beads, the type of resin, the glass transition temperature, and the like are specified to improve scratch resistance.

Japanese Patent Laid-Open No. 5644983 JP, 2008-94085, A JP, 2008-161735, A

As seen in Patent Documents 1 to 3, organic resin-coated steel sheets (precoated steel sheets) excellent in scratch resistance have been developed, and they include beads in the resin coating film in order to prevent scratches. .. However, the present inventor has found a problem that pressure marks (PM) are generated by the beads added to the coating for improving the scratch resistance.

Generally, an organic resin-coated steel sheet is wound into a coil after being coated with the organic resin coating. When the pressure at the time of winding the coil or the pressure received from the floor surface or the like at the time of storing the coil (reaction by the self weight of the coil) is high, the beads contained in the resin coating are deformed and uneven appearance occurs. This poor appearance is called a pressure mark. (See Figure 1)

In addition, in any of Patent Documents 1 to 3, there is no description or suggestion of solving the pressure mark. Further, the organic resin-coated plated steel sheet is also required to have excellent work adhesion, corrosion resistance, and whitening resistance.

Therefore, the present invention has been made in view of the above problems, and the object of the present invention is to provide scratch resistance, beauty, processing adhesion, corrosion resistance, whitening resistance, and pressure mark resistance. An object is to provide an improved, new and improved organic resin-coated plated steel sheet.

In order to solve the above problems, according to an aspect of the present invention, an organic resin coating α formed on one surface of the zinc plating layer, and a coating β formed on the other surface of the zinc plating layer an organic resin-coated plated steel sheet comprising, in the organic resin film alpha, melamine resin, glass transition temperature 0 ° C. to 20 ° C. of the polyester resin, and as would fall crosslinking reaction of melamine resin and polyester resin, the organic resin film alpha is 1 to 15 mass% of the mass as a reference for the dispersion at a ratio of beads a is 5 to 1000 pieces / mm ^2, the beads contained in the organic resin film α is only beads a, the thickness of the organic resin film α When t and the average particle diameter of the beads A are φ, 5 μm≦t≦15 μm and 1.1×t≦φ≦10×t, and the organic resin coating α and the coating β are brought into surface contact and pressed at 10 MPa. At this time, the organic resin-coated plated steel sheet is provided, wherein the apparent strain of the beads A is 20% or less.

Here, the beads A may be urethane resin beads having a glass transition temperature of −60° C. to 50° C.

The glass transition temperature of the beads A may be -40°C to 0°C.

It may also include a chemical conversion treatment film formed between the galvanized layer on one surface and the organic resin film α.

Further, the average film thickness of the coating β may be 0.5 to 2.0 μm, and the arithmetic mean roughness Ra of the surface of the coating β may be in the range of 0.3 to 2.0 μm.

Further, the organic resin coating film α may contain 3 to 15% by mass of carbon black, 1 to 10% by mass of calcium-modified silica, and 0.5 to 5% by mass of epoxy resin.

According to the present invention, an organic resin-coated steel sheet having improved scratch resistance, beauty, and pressure mark resistance is provided. Furthermore, surprisingly, it has become possible to obtain other beneficial effects through the improvement of PM. Specifically, in the processing such as pressing of the organic resin-coated steel sheet, the workability is improved (whitening does not occur even in large processing and the processing adhesion is excellent), and the back surface of the organic resin-coated steel sheet has conductivity. This brings about such effects as improving the corrosion resistance of the organic resin-coated steel sheet. That is, there is provided a new and improved organic resin-coated plated steel sheet having improved scratch resistance, beauty, processing adhesion, corrosion resistance, whitening resistance, and pressure mark resistance.

It is a conceptual diagram explaining the generation mechanism of a pressure mark. It is sectional drawing of the organic resin coating plated steel plate which concerns on this embodiment. It is a conceptual diagram explaining measurement of apparent strain.

The organic resin-coated plated steel sheet according to the present embodiment is an organic resin-coated plating including an organic resin coating α formed on the zinc-plated layer on one surface and a coating β formed on the zinc-plated layer on the other surface. A steel sheet, wherein the organic resin film α contains a melamine resin, a polyester resin having a glass transition temperature of 0° C. to 20° C., and a crosslinking reaction product of the melamine resin and the polyester resin, and 1 to 15% by mass of beads A. 5 μm≦t≦15 μm, 1.1×t≦φ≦10, where t is the thickness of the organic resin coating α and φ is the average particle size of the beads A dispersed at a rate of 5 to 1000 particles/mm ^2. Xt, and when the organic resin coating α and the coating β are brought into surface contact with each other and pressed at 10 MPa, the apparent strain of the beads A is 20% or less.

As shown in FIG. 2, the organic resin-coated plated steel sheet according to the present embodiment has an organic resin film α formed on the zinc plating layer on one surface of the galvanized steel sheet, and the other surface (the surface opposite to α). Then, the coating β is formed.

The type of galvanized steel sheet used in this embodiment is not particularly limited. The galvanized steel sheet is, for example, hot-dip galvanized steel sheet, electrogalvanized steel sheet, zinc-nickel alloy plated steel sheet, alloy hot-dip galvanized steel sheet, aluminum-zinc alloy plated steel sheet, zinc-aluminum-magnesium alloy plated steel sheet, zinc-vanadium. Any generally known zinc-based plated steel sheet such as a composite plated steel sheet may be used.

Beads A are dispersed in the organic resin coating α, where 1.1×t≦φ≦10, where t is the thickness of the organic resin coating α and φ is the average particle diameter of the beads A. The condition of xt is satisfied. Since the average particle diameter φ of the beads A is larger than the film thickness of the organic resin coating α, at least a part of the beads A is always exposed or protruding from the organic resin coating α. Therefore, when any substance comes into contact with the organic resin-coated plated steel sheet of the present embodiment, the substance is likely to come into contact with the exposed portion (protruding portion) of the bead A and is unlikely to come into contact with the organic resin coating α. This suppresses damage to the organic resin film α. That is, excellent scratch resistance can be obtained. When the average particle diameter φ of the beads A is less than 1.1 times the film thickness t of the organic resin coating film α, the beads A are not sufficiently exposed and excellent scratch resistance cannot be obtained. As the average particle diameter φ of the beads A becomes larger than 1.1 times the film thickness of the organic resin film α, the exposed portion of the beads A becomes larger and the scratch resistance is improved. However, if the average particle diameter φ of the beads A becomes too large, the amount of the organic resin film α for adhering the beads A relatively decreases, and the adhesion between the resin α and the beads A becomes insufficient, and the beads A A may fall off from the organic resin film α, and as a result, excellent scratch resistance may not be obtained. Therefore, the average particle diameter φ of the beads A is 10 times or less the film thickness t of the organic resin coating film α.

The film thickness (average film thickness) t of the organic resin film α is calculated by the following method. That is, the cross section of the sample is observed by FE-SEM to obtain the maximum thickness in the field of view of 10,000 times in the absence of the beads A, and 10 fields of view are arbitrarily observed and the average of 10 points (arithmetic mean) is calculated as the film thickness t And it is sufficient. In the following examples, the film thickness t was measured by this method.

The average particle diameter φ of the beads A can be obtained by a method of repeating microscopic observation of a sample cross section and polishing of the same cross section. That is, it can be said that the particle diameter of the beads A observed in the visual field is the diameter of the cross section perpendicular to the diameter direction of the beads A, that is, the cross sectional diameter. Therefore, the cross-sectional diameter of the beads A gradually increases with each repetition of polishing, and eventually reaches the maximum value. This maximum value corresponds to the particle size of beads A. When the polishing is further continued, the cross-sectional diameter is reduced. Therefore, the particle diameter (cross-sectional diameter) of the beads A observed in a certain visual field is measured every time polishing is performed, and the maximum measured value is set as the particle diameter of the beads A. The arithmetic average value of the maximum particle diameters of 20 beads A arbitrarily selected is defined as the average particle diameter φ. Here, the beads having the maximum particle size (cross-sectional diameter) observed in the first polishing may be smaller than the actual particle size, and are therefore excluded from the target when obtaining the average value.

The observation method and the polishing method are not particularly limited, and known methods can be adopted. For example, resin embedding polishing or microtome processing can be used. In order to obtain the average particle diameter of the beads A with a particularly high accuracy, Cryo Scanning Electron combined with Focused Ion Beam (SEM) is suitable as the polishing method. Since the sample temperature is set to about -100°C and the sample is processed with an ion beam, there is little damage to the coating film due to heat generated by ion beam irradiation, and polishing in sub-nanometer units is possible. Can also determine the particle size. In the examples described below, the average particle size was calculated using Cryo FIB-SEM.

Further, when the organic resin coating α and the coating β are brought into surface contact and pressed at 10 MPa, the apparent strain becomes 20% or less. 10 MPa is the maximum contact surface pressure between the organic resin film α containing the beads A and the film β on the back surface, which is calculated from the winding tension of the coil. The pressure received from the floor or the like during storage of the coil (reaction by the weight of the coil) depends on the weight of the coil, but is usually 10 MPa or less. The present inventor has found that the pressure mark is due to the uneven appearance caused by the deformation of the beads contained in the resin coating due to the pressure, and the apparent strain of the beads A when pressed at 10 MPa is 20% or less. If so, they found that the pressure mark could be improved. That is, by using the beads A having this specific apparent strain, excellent PM resistance can be obtained. If the apparent strain exceeds 20%, the deformation becomes large and sufficient PM resistance cannot be obtained. The apparent strain of beads A can be measured by the following method. That is, the organic resin coating α containing beads and the coating β on the back surface are brought into contact with each other and pressed at a pressure of 10 MPa, and the exposed bead height before and after the pressing (bead A exposed from the organic resin coating α, beads A The height) is observed and measured with a laser microscope (VK9710 manufactured by Keyence Corporation). Then, as shown in FIG. 3, the apparent strain ε of the beads is represented by the formula ε=(h ₀ −h, where h _{0 is} the height of the exposed bead portion before pressing and h ₁ is the height of the exposed portion after pressing. ₁ )/h ₀ (see FIG. 3). In the examples described below, the apparent strain was measured by this method.

However, when the present inventor further examined the parameters that affect the PM resistance, parameters other than the apparent strain (for example, the ratio φ/t of the particle diameter of the beads A and the organic resin coating α) were also evaluated. It became clear that it affects the PM property.

The beads A may be dispersed in the organic resin film α at a rate of 5 to 1000 beads/mm ² . In order to obtain excellent scratch resistance, it is preferable that the dispersion rate (dispersion rate) of the beads A is high. When the dispersion rate of the beads A is less than 5/mm ² , the amount of the beads A dispersed in the organic resin coating α is small and sufficient scratch resistance cannot be obtained. As the dispersion rate of the beads A becomes higher, the amount of the beads A increases and the scratch resistance is improved. However, if the dispersion rate of the beads A becomes too high, the amount of the organic resin coating film α for adhering the beads A relatively decreases, and the adhesion between the resin α and the beads A becomes insufficient. As a result, the beads A may fall off from the coating α, and excellent scratch resistance may not be obtained. Therefore, the dispersion rate of the beads A is 1000/mm ² or less.

The dispersion ratio (dispersion ratio) of the beads A can be measured by the following method. That is, the surface of the sample is observed with a microscope, the number of beads A in the visual field of 1 mm ² is measured, and the measured value is defined as the dispersion rate. It should be noted that the number of beads that completely fits within the field of view is counted as one, and the number of beads that are partially contained within the field of view is counted as 0.5. Regarding the method of displaying the dispersion ratio, if the integer part of the dispersion ratio is one digit, the number after the decimal point is rounded off, and if the integer part of the dispersion ratio is two or three digits, the number after the ones place is rounded off. When the integer part of the dispersion rate is four digits or more, the ten's place or less may be rounded off. Since the average particle diameter φ of the beads A in the present embodiment is larger than 1.1 times the thickness t of the organic resin coating α, the beads A protrude from the surface of the sample. Therefore, it can be easily counted by observing from the surface. In the examples described below, the dispersion rate of beads A was measured by this method.

Further, in order to obtain a desired dispersion rate of the beads A, the mass of the beads A may be adjusted to 1 to 15% by mass, preferably the upper limit is 10% by mass, based on the mass of the organic resin film α. Good. It is possible to obtain a desired dispersion rate of the beads A by appropriately adjusting the dispersion rate of the beads A considering that the dispersion rate of the beads A changes depending on the average particle diameter of the beads A, the specific gravity, the specific gravity of the organic resin coating α, and the like. ..

The beads A may be urethane resin beads having a glass transition temperature of −60° C. to 50° C. The glass transition temperature of the beads A is preferably -40°C to 0°C. When the glass transition temperature of beads A (hereinafter sometimes referred to as Tg) is a value within these ranges, excellent scratch resistance and PM resistance are obtained.

When the glass transition temperature of the beads A is lower than −60° C., the beads A become very soft, and sufficient scratch resistance and PM resistance may not be obtained. Further, the solvent resistance of the beads A itself is deteriorated, and the beads A are likely to swell due to the organic solvent in the coating material. In this case, the storage stability of the paint may become insufficient over time. The glass transition temperature of the beads A may be −40° C. or higher in order to enhance the scratch resistance and the stability of the paint over time. On the other hand, as the glass transition temperature increases, the beads become harder and the elasticity tends to decrease. The strain due to the pressing of the beads may be eliminated by heating or aging, but if the glass transition temperature exceeds 50° C., excellent PM resistance may not be obtained. In order to improve PM resistance, the glass transition temperature of the beads A may be 0° C. or lower.

As the urethane resin beads, those obtained by polyaddition reaction of diisocyanate and glycol, those obtained by reacting bischloroformate of glycol with diamine in the presence of a dehydrochlorinating agent, obtained by reaction of diamine and ethylene carbonate Those obtained by converting ω-amino alcohol into chloroformic acid ester or carbamic acid ester and condensing this, and those obtained by the reaction of bisurethane and diamine are used. Many of those obtained by polyaddition reaction of diisocyanate and glycol are used, many of tolylene diisocyanate (mixture of 2,4- and 2,6-) are used as diisocyanate, and one of compounds having a hydroxyl group is poly Ether-based ones such as oxypropylene glycol and polyoxypropylene-polyoxyethylene glycol and polyester-based ones obtained by condensing adipic acid and ethylene glycol are often used.

Examples of such urethane resin include "Art Pearl" (registered trademark of Negami Kogyo Co., Ltd.) manufactured by Negami Kogyo Co., Ltd., Meltex (registered trademark) manufactured by Sanyo Kasei Co., Ltd., and Dymic beads (registered Commercially available products such as trademark) can be preferably used. When the glass transition point of the beads A has a value within the above range, the apparent strain is 20% or less, and the PM resistance is improved. When the present inventor examined in detail the correlation between the glass transition point of beads A and the apparent strain, the glass transition point affects the apparent strain, but other parameters (for example, the average particle size of beads A, It was clarified that the apparent strain also fluctuates depending on the film thickness t of the organic resin film α and the ratio thereof φ/t).

The organic resin film α may include a polyester resin, a melamine resin, and a cross-linking reaction product thereof. That is, the organic resin film α may be a resin obtained by cross-linking a polyester resin and a melamine resin.

The glass transition temperature of the polyester resin may be 0°C to 20°C. When the glass transition point is lower than 0°C, the organic resin film α becomes very soft. Therefore, even if the beads A are dispersed in the organic resin coating α, the organic resin coating α may easily be flawed during pressing of the organic coated plated steel sheet. That is, excellent scratch resistance may not be obtained in some cases. On the other hand, when the glass transition point exceeds 20° C., the organic resin film α becomes extremely hard. As a result, the organic resin film α may be whitened during the press working of the organic coated plated steel sheet. The whitening is a phenomenon in which a crack is generated in the organic resin film α and the underlying zinc plating layer is transparent and looks white. By setting the glass transition temperature to 0° C. to 20° C., the organic resin film α after the crosslinking reaction becomes moderately soft, so that the organic resin film α can have both scratch resistance and whitening property. Further, when wound as a coil, the facing organic resin coating α and the coating β on the back surface are in contact with each other, and the blocking phenomenon of heat fusion due to the coil temperature during winding can be suppressed.

The film thickness t of the organic resin film α may be 5 to 15 μm. When the film thickness of the organic resin film α is less than 5 μm, the corrosion resistance may be insufficient, and the desired beauty (blackness) may not be obtained in the obtained organic coated steel sheet. Therefore, the lower limit of the film thickness of the organic resin film α may be 5 μm. Further, if the film thickness is 5 μm or more, there is no particular need to set an upper limit, but if it exceeds 15 μm, an appearance defect due to bumping marks generated in the process of drying and curing the coating material (such an appearance defect is referred to as “armpit appearance” "," armpit," or "boiling") may occur. Therefore, the upper limit of the film thickness may be 15 μm. When the film thickness of the organic resin film α is 5 to 15 μm within this range, excellent corrosion resistance and desired beauty (blackness) can be obtained, and appearance defects due to bumping marks can be avoided.

As the polyester resin which is the main resin of the organic resin film α, for example, an alkyd resin, an unsaturated polyester resin, a modified alkyd resin, or the like is used. The alkyd resin has a skeleton of a condensate of a polybasic acid such as phthalic anhydride and a polyhydric alcohol such as glycerin, and is modified with a fatty acid oil. Depending on the type and content of fats and oils used, they are classified into short oil alkyd resins, medium oil alkyd resins, long oil alkyd resins, and ultralong oil alkyd resins. The unsaturated polyester resin is synthesized by esterifying an unsaturated polybasic acid or a saturated polybasic acid and glycols. Phthalic anhydride, isophthalic acid, terephthalic acid and adipic acid are used as the polybasic acid, and propylene glycol is often used as the glycol. As the modified alkyd resin, a resin modified with a polymerizable monomer such as natural resin, phenol resin or styrene is used. Any generally known polyester resin may be used.

Examples of such a polyester resin include “Byron ^™ ” (registered trademark of Toyobo Co., Ltd.) manufactured by Toyobo Co., Ltd., “Desmofen ^™ ” (registered trademark of Sumika Bayer Urethane Co., Ltd.) manufactured by Sumika Bayer Urethane Co., Ltd., and the like. It is possible to use the product to satisfy the above glass transition temperature.

The melamine resin acts as a curing agent, and the degree of crosslinking with the polyester resin can be adjusted. This makes it possible to adjust the hardness of the organic resin film α to an appropriate range that is neither too soft nor too hard. If the degree of cross-linking is low and the organic resin coating α is too soft, even if the beads A are dispersed in the organic resin coating α, the organic resin coating α may be easily flawed during pressing of the organic coated steel sheet. .. On the other hand, if the organic resin coating α is too hard, cracking may occur in the organic resin coating α when the organic coating steel sheet is pressed, and the underlying zinc plating layer may appear white, that is, whitening may occur. .. Further, the melamine resin is not only easy to be made into a paint by dissolving it in an organic solvent, but even though the paint has a long life at room temperature, a cross-linking reaction easily progresses in a short time when heat is applied, so that the beads A Since the dispersibility is good and the paintability is also excellent, it becomes easy to apply the paint to the surface of the plated steel sheet.

The melamine resin may be a generally known melamine resin. For example, fully alkylated methylated melamine, imino group methylated melamine, methylolated melamine, methylol group methylated melamine, fully alkyl type mixed etherified melamine, methylol group mixed etherified melamine, imino group mixed etherified melamine Melamine resin and the like. As a more specific example, commercially available, for example, CYTEC Co., Ltd. Amino resin "CYMEL ^TM Series" and "MYCOAT ^TM Series", manufactured by Mitsui Chemicals, Inc. of amino resin "U-VAN ^TM Series", manufactured by DIC Corporation "Super Beckamine ^TM series" and the like.

The organic resin film α may contain 3 to 15% by mass of carbon black based on the mass of the organic resin film α. Carbon black acts as a black pigment of the organic resin film α, and can achieve desired beauty (blackness). If the carbon black concentration is less than 3% by mass, sufficient blackness may not be obtained. A high carbon black concentration improves the design. However, if the carbon black concentration exceeds 15% by mass, the corrosion resistance and chemical resistance tend to decrease, so the carbon black concentration is preferably less than 15% by mass. The mass% is based on the total mass of the organic resin film α including other constituent elements in addition to carbon black. Carbon black is preferable as the black pigment, but other coloring pigments may be used in combination. The carbon black is not particularly limited, but known carbon blacks such as furnace black, Ketjen black, acetylene black, channel black and the like can be used. Also, known carbon black subjected to ozone treatment, plasma treatment, and liquid phase oxidation treatment can be used. The particle size of carbon black used is not particularly limited as long as there is no problem with dispersibility in coating materials, coating film quality, and paintability. Specifically, primary particle diameters of 10 to 120 nm can be used. Is. Considering the designability (colorability, hiding property) and corrosion resistance of the thin film, it is preferable to use fine particle carbon black having a primary particle diameter of 10 to 50 nm. It is generally difficult to disperse these carbon blacks with the primary particle size as they are, because agglomeration occurs in the process of dispersion in the paint. That is, actually, it exists in the paint in the form of secondary particles having a particle size larger than the primary particle size, and also exists in the same form in the black coating film formed from the paint.

The organic resin film α may contain 1 to 10% by mass of calcium-modified silica based on the mass of the organic resin film α. The calcium-modified silica acts as a rust preventive pigment for the organic resin film α, and can achieve beauty over a long period of time. Furthermore, since the calcium-modified silica is hard in itself, it increases the hardness of the organic resin film α and improves scratch resistance. If the amount of calcium-modified silica is less than 1% by mass, the rust resistance and scratch resistance may not be sufficiently improved. If the concentration of calcium-modified silica is high, rust resistance and scratch resistance are improved. However, if the calcium-modified silica exceeds 10% by mass, the ratio of the other constituents of the organic resin coating α may be relatively reduced, and sufficient performance may not be obtained. It is preferably less than. The mass% is based on the total mass of the organic resin film α including other constituent elements in addition to the calcium-modified silica.

The organic resin film α may contain 0.5 to 5% by mass of an epoxy resin based on the mass of the organic resin film α. The epoxy resin enhances the adhesion between the organic resin film α and the plated steel plate, and can suppress the peeling of the organic resin film α when the resin-coated plated steel plate is processed. Further, the adhesion between the organic resin film α and the beads A is also improved, which also contributes to the improvement of excellent scratch resistance and PM resistance. If the epoxy resin content is less than 0.5% by mass, the adhesion may not be sufficiently improved. When the epoxy resin concentration is high, the adhesion is improved. However, when the epoxy resin concentration exceeds 5% by mass, the ratio of the other constituents of the organic resin coating film α relatively decreases, and sufficient performance may not be obtained, so the epoxy resin concentration is less than 5% by mass. It is preferable that The mass% is based on the total mass of the organic resin film α including other constituent elements in addition to the epoxy resin. As the epoxy resin, a bisphenol A type epoxy resin, an acrylic modified epoxy resin, a bisphenol F type epoxy resin, or the like can be used.

A chemical conversion treatment film may be formed between the galvanized layer and the organic resin film α. As a result, the adhesion of the organic resin coating α to the zinc plating layer is improved, and the organic resin coating α is less likely to peel off during press forming of the organic coating plated steel sheet.

The type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment that can be performed in the present embodiment include generally known chemical conversion treatments for zinc-based plated steel sheets. The chemical conversion treatment of the present embodiment may be zinc phosphate chemical conversion treatment, coating chromate treatment, electrolytic chromic acid treatment, reactive chromate treatment, chromate-free chemical conversion treatment, or the like. As a chromate-free chemical conversion treatment, a method of treating a zinc-based plating layer with an aqueous solution containing a silane coupling agent, a zirconium compound, a titanium compound, tannin or tannic acid, a resin, silica, etc. is known. The chemical conversion treatment of the present embodiment is described in JP-A-53-9238, JP-A-9-241576, JP-A-2001-89868, JP-A-2001-316845, JP-A-2002-60959, and The known chemical conversion treatment described in, for example, JP-A-2002-38280, JP-A-2002-266081, and JP-A-2003-253464 may be used. As a treatment liquid for performing these chemical conversion treatments, a commercially available chemical conversion treatment liquid, for example, a chromate treatment liquid "ZM-1300AN" manufactured by Nippon Parkerizing Co., Ltd., a chromate-free chemical conversion treatment liquid "CT-E300N" manufactured by Japan Parkerizing Co., Ltd. , A trivalent chromium chemical conversion treatment liquid "SURFCOAT (R) NRC1000" manufactured by Nippon Paint Surf Chemicals Co., Ltd. and the like.

The average film thickness of the coating β may be 0.5 to 2.0 μm. The coating β is a coating on the opposite surface (back surface) of the organic resin coating α. If the average film thickness of the coating film β is less than 0.5 μm, the back surface may not have sufficient corrosion resistance. The corrosion resistance is improved as the average film thickness of the coating film β is increased, but if it exceeds 2.0 μm, the conductivity is decreased. The organic resin-coated plated steel sheet of the present embodiment is used as a material for home appliances, building materials, civil engineering, machinery, automobiles, furniture, and the like, and in that case, conductivity is often required. If the average film thickness of the coating film β is 0.5 to 2.0 μm, it is possible to realize sufficient corrosion resistance and conductivity. The average film thickness of the film β can be measured in the same manner as the measurement of the average film thickness t of the organic resin film α. That is, the cross section of the sample is observed by FE-SEM, the maximum film thickness of the coating β is obtained in a field of view of 10,000 times, and 10 fields of observation are arbitrarily observed and an average of 10 points (arithmetic mean) is averaged. It should be thick. In the following examples, the average film thickness of the coating β was measured by this method. The electrical conductivity may be measured at 20 points using a Lorester 4 end needle. In the following examples, the conductivity of the coating β was measured by this method. In such a conductivity test, it is possible to compile how many results of 20 or less the resistance value is below the predetermined resistance value. That is, the conductivity is evaluated as 100% (20/20) if the resistance is below the predetermined resistance at all 20 points, and the conductivity is 50% (10/20) if the resistance is below the predetermined resistance at 10 points. To be done.

The arithmetic mean roughness Ra of the surface of the coating β may be in the range of 0.3 to 2.0 μm. If the arithmetic average roughness Ra is less than 0.3 μm, sufficient conductivity may not be obtained. The conductivity increases as the roughness Ra increases, but if the roughness Ra exceeds 2.0 μm, the corrosion resistance decreases. Coating β
Sufficient conductivity and corrosion resistance can be obtained by setting the arithmetic mean roughness Ra of the surface of the above in the range of 0.3 to 2.0 μm. The arithmetic mean roughness Ra may be obtained based on JIS B0601:2001. In the following examples, the arithmetic mean roughness Ra was measured by this method.

Hereinafter, this embodiment will be described in detail with reference to examples. However, the present invention should not be construed as being limited to the examples.

Under various conditions shown in Tables 1 to 3, organic resin coatings α and β in which beads A were dispersed were formed on a Zn-plated steel sheet. Using the obtained organic resin-coated plated steel sheet, each performance was measured and evaluated.

The measurement contents of each performance are as follows.
(Pressure mark property)
The surface α of the organic resin film, which is the front surface, and the film β, which is the back surface, were brought into contact with each other, hot pressed at a predetermined pressure and temperature for 1 hour (pressurizing time), and the appearance after the test was visually observed.
<Evaluation criteria>
⊚: PM cannot be seen at all even when it is obliquely viewed
◯: PM is slightly visible when viewed from an angle.
○ △: PM is clearly visible from an angle.
Δ: Slightly visible when observed from the front.
X: PM is clearly visible from the front.

(Scratch resistance)
Each test material was brought into close contact with an electrogalvanized steel sheet (untreated material), and the test material was rotated 90° under pressure. The pressurization was 0.5 kg/cm ² , and the test temperature was 25°C. Then, the appearance of the test material was visually evaluated.
<Evaluation criteria>
○: No scratches are visible ○ △: There are small scratches, but the base material is not exposed △: The base material is slightly exposed (exposed area: less than 9%)
×: bare substrate exposed (exposed area: 9% or more)

(Backside conductivity)
The electrical conductivity was measured at 20 points using a four-point Lorester needle.
<Evaluation criteria>
In such a conductivity test, the number of 20 points where the resistance value was 1 mΩ or less was calculated. If all the 20 points are below the predetermined resistance value, the conductivity is evaluated as 100% (20/20), and if the 10 points are below the predetermined resistance value, the conductivity is evaluated as 50% (10/20). ..

(Process adhesion)
After performing 0T bending (180° bending) and peeling off the tape on the outside of the bent portion, the state of coating film adhesion on the tape side was observed and evaluated according to the following evaluation criteria. In this adhesion test, when the rating is ◯ or higher, the adhesion was excellent, and Δ or higher was judged to be acceptable.
<Evaluation criteria>
○: No coating film adhered on the tape side △ △: Less than a few percent of the steel sheet side peeled off on the tape side △: Steel sheet with several points peeled off the tape side Peeling on the side is less than 9% x: Coating film peeling on the tape side, peeling on the steel plate side is 9% or more

(Stability of paint over time)
After the paint was prepared, it was aged at a temperature of 40° C. for 1 month. The paint that had deteriorated with time was applied to a steel plate, and the baked plate was visually and visually observed with a 30-fold magnifier.
<Evaluation criteria>
○: No solid matter in paint ○ △: Small solid matter in the paint, but it is not visible visually △: Solid matter in the paint, visible visually ×: The paint solidifies and cannot be applied

(Blackness)
Gloss measuring device (Product name: Uni
The 60-degree gloss value of the test piece was measured using Gloss 60Plus (manufactured by Konica Minolta). Further, the L* value of the test piece was measured using a color difference meter CR-400 (manufactured by Konica Minolta).
<Evaluation criteria>
The conventional product 9.2 was used as the standard for the 60-degree gloss value, and the conventional product 27 was used as the standard for the L* value. Those that satisfied the standard values of these conventional products were marked with ◯, and those that did not meet were marked with x. The case where only one of them was satisfied was designated as Δ.

(Corrosion resistance (front))
The organic resin film α on the front side of the test piece was extruded by 6 mm with an Erichsen tester (according to A dimension of JIS Z 2247) at the central portion thereof, and the end surface was tape-sealed and conformed to JIS Z 2371. The salt spray test (SST) was performed for 120 hours, and the rust generation state of each of the extruded portions after each test time was observed and evaluated according to the following evaluation criteria.
<Evaluation criteria>
◎: White rust occurrence area is less than 1% ○: White rust occurrence area is 1% or more and less than 5% ○ △: White rust occurrence area is 5% or more and less than 10% △: White rust occurrence area is 10% or more, Less than 30% x: White rust occurrence area is 30% or more

(Corrosion resistance (back))
For the coating β on the back side of the test piece, the same corrosion resistance evaluation as the organic resin coating α was performed.

(Whitening of processed part)
Erichsen processing was performed until the test piece broke, and the degree of whitening was visually evaluated.
<Evaluation criteria>
○: No whitening ○ △: Whitening is observed only in the vicinity of the fractured part.
B: Whitening is observed in places other than the fractured part.
×: Whitening occurs on the entire surface

(appearance)
The appearance of the organic resin film α was visually evaluated.
<Evaluation criteria>
○: No side appearance ×: Side appearance

(Comprehensive evaluation)
In each performance evaluated, the result with the worst performance was reflected and it was set as the comprehensive evaluation.
<Evaluation criteria>
○: Passed (excellent)
○ △: Passed (good)
△: Passed (OK)
×: Fail

With reference to the condition of #1, the influence on the performance item was observed when the condition (numerical value) of the specific item was variously changed within the preferable range of this embodiment. In #2 to #5, #33 to 42 and #47, any one of the average particle diameter (φ) of the beads A, the thickness (t) of the organic resin coating α and φ/t is changed. Outside the preferred range of 1, the pressure mark resistance, scratch resistance, processing adhesion, blackness, corrosion resistance (front), and appearance were inferior.

In #6 to #8, the apparent strain of the beads A was changed, and the pressure mark resistance was inferior outside the preferable range of this embodiment. In #9 to #12 and #33 to 37, the dispersion ratio of the beads A was changed, and outside the preferable range of this embodiment, the scratch resistance or the work adhesion was poor. In #13 to #18, the glass transition temperature (Tg) of the beads A was changed, and outside the preferable range of this embodiment, the scratch resistance, the temporal stability of the coating, or the pressure mark resistance was poor. It was In #19 to #23, the additive to the organic resin film α was changed, and outside the preferred range of this embodiment, the processing adhesion, the blackness, or the corrosion resistance (front and back) was poor.

The sample No. 24 was not subjected to the chemical conversion treatment, and was inferior to the sample subjected to the chemical conversion treatment in the work adhesion, although it was in an allowable range. In #25 to #32, the film thickness and the surface roughness of the coating film β were changed, and the conductivity or the corrosion resistance (back) was inferior outside the preferred range of this embodiment.

In #43 to #46, the glass transition temperature of the polyester contained in the organic resin film α was changed, and outside the preferred range of this embodiment, the scratch resistance and the whitening of the processed portion were inferior.

The preferred embodiments of the present invention have been described in detail above with reference to the accompanying drawings, but the present invention is not limited to these examples. It is obvious that a person having ordinary knowledge in the technical field to which the present invention pertains can come up with various changes or modifications within the scope of the technical idea described in the claims. Of course, it is understood that these also belong to the technical scope of the present invention.

Claims (6)

An organic resin coating α formed on the zinc plating layer on one surface, and an organic resin coating plated steel sheet including a coating β formed on the zinc plating layer on the other surface,
The organic resin coating α contains a melamine resin, a polyester resin having a glass transition temperature of 0° C. to 20° C., and a cross-linking reaction product of the melamine resin and the polyester resin, and is 1 based on the mass of the organic resin coating α. ˜15% by mass of beads A are dispersed at a rate of 5 to 1000 beads/mm ² ,
The beads contained in the organic resin coating α are only the beads A,
When the thickness of the organic resin film α is t and the average particle diameter of the beads A is φ, 5 μm≦t≦15 μm and 1.1×t≦φ≦10×t,
An organic resin-coated plated steel sheet, wherein the apparent strain of the beads A is 20% or less when the organic resin coating α and the coating β are brought into surface contact with each other and pressed at 10 MPa. The organic resin-coated plated steel sheet according to claim 1, wherein the beads A are urethane resin beads having a glass transition temperature of -60°C to 50°C. The organic resin-coated plated steel sheet according to claim 2, wherein the glass transition temperature of the beads A is -40°C to 0°C. The organic resin-coated plated steel sheet according to any one of claims 1 to 3, further comprising a chemical conversion treatment film formed between the galvanized layer on the one surface and the organic resin film α. .. The average film thickness of the coating β is 0.5 to 2.0 μm, and the arithmetic average roughness Ra of the surface of the coating β is in the range of 0.3 to 2.0 μm. The organic resin-coated plated steel sheet according to any one of items 1 to 4. The organic resin coating α contains 3 to 15% by mass of carbon black, 1 to 10% by mass of calcium-modified silica, and 0.5 to 5% by mass of epoxy resin. The organic resin-coated plated steel sheet according to any one of items.

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