JP5644983B1 - Organic coated galvanized steel sheet and method for producing the same - Google Patents

Abstract

For the purpose of reducing production costs, the mold maintenance cycle is extended, the mold surface is wrinkled so that the mold can be operated maintenance-free, and even if the surface is pressed with a rough mold, wrinkles, etc. It is an object of the present invention to provide an organic-coated galvanized steel sheet that is less susceptible to film damage. According to the present invention, the above-described problem is that in the zinc-based plated steel sheet 11 in which the organic coating 15 including the beads 14 is coated on at least one side of the zinc-based plating layer 13, the organic coating 15 has a thickness t, and the beads 14. The organic coated zinc-based plated steel sheet 10 includes beads 14 having a particle diameter satisfying a condition of φ> 3t, and a glass transition point of a resin constituting the beads is higher than 150 ° C. Reached by.

Description

  The present invention relates to an organic-coated galvanized steel sheet and a method for producing the same, and more specifically, as a material for home appliances, building materials, civil engineering, machinery, automobiles, furniture, and the like without being subjected to further coating after press molding. The present invention relates to an organic-coated galvanized steel sheet that can be used and a method for producing the same. The organic-coated zinc-based plated steel sheet of the present invention suppresses mold galling and wrinkle generation particularly during press molding, and is excellent in press oil retention.

  Organic coated galvanized steel sheet that is provided with corrosion resistance, fingerprint resistance, color tone, etc. by coating an organic coating on the surface of the galvanized steel sheet as an organic coated galvanized steel sheet used in home appliances, building materials, automobiles, etc. Has been applied. Such an organic-coated zinc-based plated steel sheet is often used as a material for home appliances, building materials, automobiles and the like without being subjected to further painting after being pressed. In general, press forming of such an organic-coated zinc-based plated steel sheet is performed using a mold having no surface defects in order to prevent appearance defects such as scratches on the surface of the film and galling of the mold. . When a plurality of steel sheets are continuously pressed using a continuous press machine in a mass production press factory, wrinkles and the like enter the mold surface. For this reason, periodic mold maintenance (such as polishing the mold surface) is required. On the other hand, with the globalization of industry in recent years, these organic coated galvanized steel sheets have been exported to countries around the world and are being press-formed by various press manufacturers around the world. Different countries and regions have different press factories, and there are many press factories that cannot maintain molds due to economic and technical reasons. In addition to this, in response to the recent global economic deterioration, there are an increasing number of press manufacturers that extend the maintenance period of molds and press makers that use molds without maintenance for the purpose of reducing manufacturing costs. Therefore, organic coated galvanized steel sheet that does not easily cause film damage such as wrinkles even when pressed with a mold with a flaw on the surface or a mold with a rough surface, that is, an organic coated galvanized plating with improved scratch resistance. Steel sheets are anxious.

  On the other hand, Patent Document 1 discloses a technique for forming a clear coating film on the surface of a stainless steel plate. The clear coating film includes a thermosetting resin composition and resin beads. A thermosetting resin composition is comprised with the acrylic resin with a glass transition point of 30-90 degreeC, and the block isocyanate resin and amino resin which bridge-harden the said acrylic resin. Resin beads are included in the clear coating film at a ratio of 0.5 to 4.0 parts by mass per 100 parts by mass of the thermosetting resin composition. The clear-coated stainless steel sheet produced by this technique is expected to have improved pressure mark resistance and scratch resistance. Patent Document 1 describes that the average particle diameter of resin beads is preferably 0.2 to 3.0 times the film thickness of the clear coating film.

JP2011-224975A

  However, even if an organic-coated zinc-based plated steel sheet was prepared using the technique disclosed in Patent Document 1, the scratch resistance of the organic-coated zinc-based plated steel sheet could not be sufficiently improved. Then, this invention is made | formed in view of the said problem, The place made into the objective of this invention is providing the organic coating zinc-plated steel plate which the abrasion resistance improved from the past, and its manufacturing method. is there.

  As described in Patent Document 1, by including resin beads in the clear coating film covering the stainless steel plate, the scratch resistance of the clear coated stainless steel plate is improved. However, the scratch resistance of the organic-coated zinc-based plated steel sheet cannot be sufficiently improved by simply applying this technique to the organic-coated zinc-based plated steel sheet. Specifically, the number of pressure marks generated when the organic-coated zinc-based plated steel sheet was wound, the number of crumbs generated when the steel sheets were rubbed with each other, or when the steel sheet and other materials were rubbed, decreased.

  However, when the organic-coated zinc-based plated steel sheet was pressed with a mold having a flaw on the surface or a mold having a rough surface, the organic-coated zinc-based plated steel sheet still had many scratches. For this reason, the inventors have intensively studied to solve the above problems, and as a result, when the organic coating includes beads that are more than three times the thickness of the organic coating, the scratch resistance of the organic coated zinc-based plated steel sheet is reduced. I found a great improvement. Specifically, when the organic-coated zinc-based plated steel sheet was pressed using a mold having a flaw on the surface or a mold having a rough surface, the number of scratches was greatly reduced.

  However, it has been very difficult to stably add beads having a particle size much larger than the film thickness of the organic coating to the organic coating in a mass production line. The inventor tried to apply a paint containing large-diameter beads on a steel plate by using a roll coater coating which is widely used. As a result, when adjusting the peripheral speed difference between the rolls (specifically, the peripheral speed difference between the pickup roll and the applicator roll, or the peripheral speed difference between the pickup roll and the doctor roll) and the nip thickness, The diameter beads have been squeezed out of the steel plate. For this reason, the large particle size beads were not mixed in the organic film applied on the steel plate.

  As a result of the above experiment, it is difficult for a roll coater to mix beads having a maximum particle diameter of 1.5 times or more of the film thickness of the organic film, and even if the coating conditions are adjusted, the film thickness of the organic film It has been found that it is a limit to mix beads having a maximum particle size of 3.0 times the organic film into the organic film. In addition, when a paint containing beads having a large particle size with respect to the film thickness is applied with a roll coater, an appearance defect generally called a living room or a streaky appearance defect such as dragging beads occurs. Therefore, it was difficult to mix large particle size beads into the organic film.

  Therefore, the inventors further studied, and when the zinc-based plated steel sheet was coated using a curtain coater that can apply the paint in a non-contact manner to the zinc-based plated steel sheet to be coated Furthermore, it has been found that large-diameter beads can be mixed into the organic film relatively easily. However, even when a curtain coater is used, it has been difficult to apply beads having a large particle size more than three times the film thickness of the organic coating to a zinc-based plated steel sheet.

  Therefore, the inventor pays attention to the physical properties of the organic film and controls the physical properties of the organic film, so that beads having a large particle size more than three times the film thickness of the organic film can be easily applied to the zinc-based plated steel sheet. It has been found that it can be applied. Specifically, the inventor has found that the organic film is preferably composed of a polyester resin having a large number average molecular weight, a small hydroxyl value, and a relatively low glass transition point (that is, relatively soft). did. A resin having a large number average molecular weight and a small hydroxyl value has a molecular structure with few branches and a relatively straight chain, and this linear molecular chain has a relatively long structure. When the molecular chain of the resin is long, the viscosity of the paint increases, and the large particle size beads in the paint become difficult to settle during coating. For this reason, it becomes easy to mix a large particle size bead in an organic membrane | film | coat by coating a zinc-based plated steel plate using a curtain coater. Further, the inventor found that if the resin molecular chain is long, the resin tends to get entangled with the beads, so that the resin can easily cover the bead surface even after coating, and if the glass transition point of the resin covering the bead surface is low, They also found it difficult to detach.

  The present invention has been completed based on such knowledge, and the gist of the present invention is as follows.

1) In a steel sheet in which an organic coating containing beads is coated on at least one surface of a zinc-based plating layer, the organic coating is a grain satisfying the condition of φ> 3t, where t is the film thickness and φ is the particle size of the beads. wherein the diameters of beads, including glass transition point of the resin constituting the beads rather greater than 0.99 ° C., when observed any cross-sectional length 20 mm, the organic film is phi> 3t satisfying beads one or more of An organic-coated galvanized steel sheet.

3) The organic-coated zinc-based plated steel sheet according to 1) or 2) above, wherein the beads are covered with an organic film.

4) The organic-coated galvanized steel sheet according to any one of 1) to 3) above, wherein the film thickness of the organic film is 3 to 20 μm.

5) The organic coated galvanized steel sheet according to any one of 1) to 4) above, wherein the organic film contains a colored pigment in addition to the beads.

6) The main resin of the organic film has a number average molecular weight of 13,000 to 30,000, a hydroxyl value of 10 KOH mg / g or less, a glass transition point of 3 to 50 ° C., 100 parts by mass of polyester resin and 15 to 30 parts by mass of amino resin, The organic-coated zinc-based plated steel sheet according to any one of 1) to 5) above, which is characterized by comprising:

7) The glass transition point of the polyester resin is 3 to 20 ° C. The organic-coated zinc-based plated steel sheet according to 6) above.

8) The organic coated zinc-based plated steel sheet according to 6) or 7) above, wherein the polyester resin has a hydroxyl value of 5 KOHmg / g or less.

9) The organic coated zinc-based plated steel sheet according to any one of 1) to 8) above, wherein a chemical conversion treatment is performed between the zinc-based plated layer and the organic film.

9) By applying a paint containing beads on a galvanized steel sheet with a curtain coater and then drying and baking, the condition of φ> 3t is satisfied when the film thickness of the organic film is t and the particle size of the beads is φ. the organic wherein the particle diameter of beads, including glass transition point of the resin constituting the beads rather greater than 0.99 ° C., when observed any cross-sectional length 20 mm, phi> 3t satisfying beads one or more of which satisfy A production method for obtaining an organic coated zinc-based plated steel sheet coated with a film.

  According to the present invention, there is provided an organic-coated zinc-based plated steel sheet that is resistant to film damage such as wrinkles even when pressed with a mold having a flaw on the surface or a mold having a rough surface (that is, improved scratch resistance). It became possible to do. As a result, operations such as extending the maintenance cycle of the mold and using the mold without maintenance can be performed, and the production cost can be reduced at a press maker than before, and the product can be manufactured at a low cost. In addition, even press manufacturers that do not have mold maintenance technology can use organic-coated galvanized steel sheets, and the applications for these steel sheets have expanded. Furthermore, since the curtain coater is simpler than the roll coater, it can be easily incorporated into the plating line. Thereby, a plating process and the coating process of an organic film can be performed only by one line (plating line). Furthermore, since the organic film satisfies the condition that the particle diameter is φ> 3t and includes beads having a glass transition point of greater than 150 ° C., the scratch resistance of the organic coated zinc-based plated steel sheet is improved even if the organic film is thinned. Furthermore, the surface of the organic-coated zinc-based plated steel sheet according to the present invention is not easily distorted even when levelered. For example, an organic-coated zinc-based plated steel sheet is less likely to drop off its surface beads even when leveled. Therefore, the present invention can be said to be an industrially highly valuable invention.

It is a schematic diagram explaining the organic coating zinc-based plated steel plate of this invention. It is an example of the cross-sectional microscope observation photograph of the organic covering zinc-based plated steel plate of this invention. It is a figure explaining the flat plate sliding test done in the Example.

  As shown in FIG. 1, the organic-coated zinc-based plated steel sheet 10 according to this embodiment includes a zinc-based plated steel sheet 11 and an organic film 15 that covers at least one surface of the zinc-based plated steel sheet 11. The zinc-based plated steel sheet 11 includes a steel sheet 12 and a zinc-based plated layer 13 provided on the surface thereof. The organic film 15 includes beads 14 that satisfy the condition of φ> 3t. Here, t is the film thickness of the organic film 15, and φ is the particle size (diameter) of the beads 14.

  As shown in FIG. 1, the film thickness t of the organic film 15 corresponds to the film thickness in a portion of the organic film 15 whose surface is substantially parallel to the surface of the plating layer 13. When φ is 3 t or less, when the organic-coated galvanized steel sheet 10 is pressed with a rough surface mold or a mold containing wrinkles, wrinkles are likely to enter the surface of the coating. Therefore, beads with φ of 3 t or less are not suitable for this embodiment.

  The number of beads 14 (that is, beads satisfying the condition of φ> 3t) is not particularly limited. However, when one or more beads 14 are found when observing an arbitrary cross section of the organic coated zinc-based plated steel sheet 10 with a length of 20 mm, it becomes difficult for wrinkles to enter the surface of the coating during press working. Therefore, it is preferable that one or more beads 14 exist in an arbitrary cross section of the organic coated zinc-based plated steel sheet 10 having a length of 20 mm.

  A suitable example of the method for observing the cross section of the organic coated zinc-based plated steel sheet 10 is as follows. That is, the organic-coated zinc-based plated steel sheet 10 is cut along an arbitrary cross section having a length of 20 mm, and the cross section is embedded in the resin so that the steel sheet is perpendicular to the resin surface. Then, the cross section is polished (this method is also called resin embedding polishing). Then, the cross section is observed with an optical microscope or an electron microscope.

  When the cross section is observed with a microscope or the like, it is difficult to capture the true long diameter cross section of the bead. However, if the diameter of the cross section of the bead observed in the cross section is larger than 3t, the bead can be determined as a bead satisfying the condition of φ> 3t, that is, the bead 14. Therefore, the number of beads 14 can be measured by the above method. An example of a cross-sectional microscopic observation photograph of the organic coated zinc-based plated steel sheet 10 is shown in FIG. The upper limit of the number of beads 14 existing in a cross section having a length of 20 mm varies depending on the particle diameter and film thickness of the beads added to the organic coating 15, and is not particularly defined. It only has to be done. However, if the number of beads 14 is too large, the beads 14 are easily detached from the organic film 15. Therefore, it is preferable to confirm beforehand the number of beads 14 not to fall off from the organic film 15 by experiments or the like.

  More specifically, in an arbitrary cross section having a length of 20 mm, the total number of beads in the cross section (the total number of beads 14 and beads for which φ is 3 t or less) is 10 or more, and the beads 14 are beads in the cross section. More preferably, it is 1.0% or more based on the total number. In this case, film damage is less likely to occur. The bead distribution can be measured by the same method as described above. Further, the distribution of the beads can be adjusted by adjusting the particle size distribution of the beads, the viscosity of the paint, and the condition of stirring the paint before painting. The particle size distribution of the beads can be adjusted by placing the beads on a classifier. The optimum conditions for these parameters are not particularly defined, and the optimum conditions may be found by conducting a test in advance.

  A preferable range of the film thickness of the organic film 15 is 3 to 20 μm. It is difficult to stably apply the paint including the beads 14 on the galvanized steel sheet 11 with a thickness of less than 3 μm using a curtain coater. In addition, when the film thickness of the organic film 15 exceeds 20 μm, appearance defects (such appearance defects and boiling) are likely to occur due to bumping marks generated during the drying and curing process of the paint. A more preferable range of the film thickness is 5 to 20 μm. When the film thickness is within this range, the corrosion resistance of the galvanized steel sheet is improved.

  The glass transition point of the beads 14 is greater than 150 ° C. The glass transition point of the beads 14 is preferably 170 to 190 ° C. Further, the melting point of the beads 14 is preferably 250 ° C. or higher. When the glass transition point and the melting point of the beads 14 are values within these ranges, film damage is less likely to occur (the scratch resistance is improved). Examples of the resin constituting the beads 14 include acrylic resins and polystyrene resins. The upper limit of the particle size of the beads 14 is not particularly defined, and can be appropriately selected as necessary. However, if the particle size of the beads 14 is too large with respect to the film thickness t, the beads 14 are easily detached from the organic film. Since the detachment of the beads 14 greatly affects the compatibility (for example, adhesion) between the coating film and the beads, it is necessary to evaluate in advance and appropriately select the beads 14 having a particle size that does not detach. However, generally speaking, the upper limit of the particle size is considered to be about 100 μm. This is because if it exceeds this, the beads 14 easily fall off from the coating film.

  Further, the surface of the beads is preferably covered with an organic film 15. As a result, film damage is less likely to occur. Moreover, it is preferable that the film thickness of the organic membrane | film | coat 15 which covers the surface of a bead is 0.1 micrometer or more. The upper limit of the film thickness of the organic film 15 covering the surface of the bead 14 is not particularly specified, but it is physically difficult to exceed the film thickness of the organic film 15 coated on the galvanized steel sheet 11, so that the zinc film The film thickness of the organic film 15 coated on the plated steel sheet 11 becomes the upper limit value. As a result, film damage is less likely to occur. In addition, when the organic film paint is applied to the galvanized steel sheet 11 using the roll coater, the organic film paint on the surface of the beads is scraped off by the roll, so it is very difficult to cover the surface of the beads 14 with the organic film 15. It is difficult to. However, since the curtain coater can apply the organic coating material to the galvanized steel plate 11 without contacting the organic coating material, the bead surface can be covered with the organic coating 15. The film thickness of the organic film 15 on the bead surface can be measured by observing the cross section of the film by the same method as the measurement of the distribution of the beads 14, and the film thickness of the organic film 15 covering the bead surface is the same as that of the organic film 15. The molecular weight and hydroxyl value of the main resin can be adjusted. That is, since a resin having a high molecular weight has a long molecular chain, the resin has a high melt viscosity and a high viscosity. For this reason, the resin having a high molecular weight easily covers the beads 14. A resin having a small hydroxyl value is composed of straight-chain molecules having few molecular chain branches. That is, a resin having a small hydroxyl value has a substantially long molecular chain, and therefore easily covers the beads 14.

  The organic film 15 may contain a coloring pigment in addition to the beads 14. By including the color pigment, design properties can be imparted to the organic film 15, which is preferable. Examples of pigments that can be added to the organic film 15 include generally known color pigments such as carbon black as a black pigment, titanium oxide as a white pigment, cadmium red as a red pigment, inorganic red pigments such as silver vermilion, and carmine 6B. Organic soluble azo red pigments such as Lake Red C and Watching Red, Permanent Red, Lake Red 4R, Organic insoluble azo red pigments such as naphthol red, Condensed azo red pigments such as chromoftal red, Yellow lead Inorganic yellow pigments such as yellow iron oxide and cadmium yellow, organic yellow pigments such as disazo yellow, monoazo yellow and condensed azo yellow, inorganic orange pigments such as molybdenum orange, and organic orange pigments such as disazo orange and permanent orange Can be used. The coloring pigment may be a generally known metallic pigment. Examples of metallic pigments include aluminum flakes, nickel flakes, stainless steel flakes, and gold foil. The color pigment may be glass flakes or resin flakes on which a metal such as aluminum is deposited. The coloring pigment may be a generally known pearl-like pigment, for example, mica coated with a metal oxide such as mica, titanium oxide, or iron oxide. The addition amount of the color pigment is not particularly limited, and may be appropriately adjusted according to the design appearance required for the organic-coated zinc-based plated steel sheet 10.

  The friction coefficient of the surface of the organic film 15 is preferably 0.17 or less. In this case, the scratch resistance of the organic-coated zinc-based plated steel sheet 10 is further improved. Examples of a method for setting the coefficient of friction of the surface of the organic film 15 to 0.17 or less include a method of adding wax to the organic film 15. The wax may be a generally known wax for paint. Examples of the coating wax include carnauba wax, fluorine wax, paraffin wax, and microcrystalline wax. A preferable addition amount of the wax is not particularly limited because it varies depending on the kind of the main resin constituting the organic film 15 and the like. That is, the friction coefficient of the surface of the organic film 15 may be set to 0.17 or less by adjusting the amount of wax added according to the type of the main resin constituting the organic film 15 and the like.

  The main resin of the organic film 15 is preferably a resin obtained by crosslinking a polyester resin with an amino resin. In addition, the main resin of this embodiment means resin with the largest mass% with respect to the total mass of the organic membrane | film | coat 15 among resin which comprises the organic membrane | film | coat 15. FIG. The number average molecular weight of the polyester resin is preferably 13,000 to 30,000, the hydroxyl value is preferably 10 KOHmg / g or less, and the glass transition point (hereinafter referred to as Tg) is 3 to 50 ° C. Preferably there is. When these conditions are satisfied, when the paint containing the beads 14 is curtain-coated on the galvanized steel sheet 11, the beads 14 are easily mixed in the paint layer, and the beads 14 are detached from the paint layer even after the mixing. Hateful.

  When the number average molecular weight of the polyester resin is less than 13,000, the paint curtain may be difficult to form during curtain coating. Moreover, even if the coating containing the beads 14 can be applied to the galvanized steel sheet 11 by another coating method, the beads 14 are likely to be detached from the organic coating 15 during the press working of the organic coated galvanized steel sheet 10. For this reason, there exists a possibility that a wrinkle may enter into the organic membrane | film | coat 15 at the time of press work.

  When the number average molecular weight of the polyester resin is more than 30,000, the viscosity of the paint is too high, and as a result, it may be difficult to paint or it may not be possible to paint. When the hydroxyl value of the polyester resin exceeds 10 KOHmg / g, the number average molecular weight of the polyester resin is small or the polyester resin becomes branched. For this reason, there is a possibility that it is difficult to form a paint curtain during curtain coating. Moreover, even if the coating containing the beads 14 can be applied to the galvanized steel sheet 11 by another coating method, the beads 14 are likely to be detached from the organic coating 15 during the press working of the organic coated galvanized steel sheet 10. For this reason, there exists a possibility that a wrinkle may enter into the organic membrane | film | coat 15 at the time of press work.

When the glass transition point of the polyester resin is less than 3 ° C., the organic film 15 becomes very soft. For this reason, even if the beads 14 are added to the organic film 15, there is a risk that wrinkles easily enter the organic film 15 during the press working of the organic coated zinc-based plated steel sheet 10. On the other hand, when the glass transition point exceeds 50 ° C., the organic film 15 becomes very hard. For this reason, the beads 14 are easily detached from the organic film 15. As a result, there is a risk that wrinkles may easily enter the organic coating 15 during the press working of the organic coated zinc-based plated steel sheet 10. The polyester resin used as the main resin of the organic film 15 may be a generally known polyester resin. Examples of such polyester resins include “Byron ^™ ” (registered trademark of Toyobo Co., Ltd.) manufactured by Toyobo Co., Ltd. and “Desmophen ^™ ” (registered trademark of Sumika Bayer Urethane Co., Ltd.) manufactured by Sumika Bayer Urethane Co., Ltd. It is done. The main resin of the organic film 15 may be a mixture of these polyester resins.

  Here, the glass transition point of the polyester resin is preferably 3 to 20 ° C, and more preferably 3 to 10 ° C. When the glass transition point is a value within these ranges, the organic film 15 becomes soft, so that even if the organic film 15 is damaged, the damage can be easily repaired. On the other hand, the glass transition point of the polyester resin may be 40 to 50 ° C. In this case, since the organic film 15 is hardened, not only is the scratch itself difficult to be scratched, but also the workability and corrosion resistance of the galvanized steel sheet 11 are improved.

  The hydroxyl value of the polyester resin is preferably 5 KOHmg / g or less, although there is a measurement limit. In this case, since the polyester resin is closer to a straight chain, it becomes easier to form a paint curtain. Therefore, it becomes easier to form the organic film 15. Furthermore, there is an advantage that it is easy to cover the beads 14 with the organic film 15.

  It is preferable to add 15 to 30 parts by mass of an amino resin to 100 parts by mass of the polyester resin. In this case, the press formability of the organic-coated zinc-based plated steel sheet 10 is more excellent. When the addition amount of the amino resin is less than 15 parts by mass, the degree of cross-linking of the organic film 15 becomes low, so that the organic film 15 becomes very soft. For this reason, the beads 14 are easily detached from the organic coating 15 when the organic coated zinc-based plated steel sheet 10 is pressed. As a result, wrinkles may enter the organic film 15.

When the addition amount of the amino resin exceeds 30 parts by mass, the organic film 15 becomes very hard. For this reason, the beads 14 are easily detached from the organic coating 15 when the organic coated zinc-based plated steel sheet 10 is pressed. As a result, wrinkles may enter the organic film 15. The amino resin that can be added to the organic film 15 may be a generally known amino resin. Examples of amino resins that can be added to the organic film 15 include fully alkyl methylated melamine, imino group methylated melamine, methylol melamine, methylol group methylated melamine, fully alkyl mixed etherified melamine, and methylol group. Melamine resins such as type mixed etherified melamine and imino group type mixed etherified melamine, butylated melamine, benzoguanamine resin, amino resin and the like. More specific examples of possible amino resin added to the organic film 15, commercially available, for example, CYTEC Co., Ltd. Amino resin "CYMEL ^TM Series" and "MYCOAT ^TM Series", manufactured by Mitsui Chemicals, Inc. of amino system resin "U-VAN ^TM Series", DIC Co., Ltd. "Super BECKAMIN ^TM Series" and the like.

  Further, the number of layers of the organic film 15 is not particularly limited, but it is preferable to form only one layer from the viewpoint of cost. Since the organic film 15 of the present embodiment includes beads 14 having a particle size satisfying the condition of φ> 3t and a glass transition point of greater than 150 ° C., even when only one layer of the organic film 15 is formed. The scratch resistance of the organic coated zinc-based plated steel sheet 10 can be greatly improved.

  It is preferable that a chemical conversion treatment is performed between the zinc-based plating layer 13 and the organic film 15 of the organic-coated zinc-based plated steel sheet 10. In this case, since the adhesion of the organic coating 15 is improved, the organic coating 15 is difficult to peel off during press forming of the organic coated zinc-based plated steel sheet 10. The type of chemical conversion treatment is not particularly limited. Examples of the chemical conversion treatment that can be carried out in the present embodiment include generally known chemical conversion treatments for galvanized steel sheets. The chemical conversion treatment of the present embodiment may be zinc phosphate chemical conversion treatment, coating chromate treatment, electrolytic chromic acid treatment, reaction chromate treatment, chromate-free chemical conversion treatment, or the like. As the 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, or the like is known. The chemical conversion treatment of this embodiment is disclosed in JP-A-53-9238, JP-A-9-241576, JP-A-2001-89868, JP-A-2001-316845, JP-A-2002-60959, Known chemical conversion treatments described in JP-A-2002-38280, JP-A-2002-266081, JP-A-2003-253464, etc. may be used. As treatment liquids for performing these chemical conversion treatments, commercially available chemical treatment liquids, for example, chromate treatment liquid “ZM-1300AN” manufactured by Nihon Parkerizing Co., Ltd., chromate-free chemical conversion treatment liquid “CT-E300N” produced by Nihon Parkerizing Co., Ltd. And trivalent chromium-based chemical conversion treatment solution “Surfcoat® NRC1000” manufactured by Nippon Paint Co., Ltd.

  It is preferable that the paint layer containing the beads 14 is applied to the galvanized steel sheet 11 with a curtain coater and then the paint layer is dried and baked. Thereby, the beads 14 are easily mixed into the organic film 15. Note that a coating apparatus other than the curtain coater, for example, a roll coater, is not suitable for this embodiment because the beads 14 can hardly be mixed into the organic film 15.

  The type of the galvanized steel sheet 11 is not particularly limited. The galvanized steel sheet 11 is generally known as a hot dip galvanized steel sheet, an electrogalvanized steel sheet, a zinc-nickel alloy plated steel sheet, an alloyed hot dip galvanized steel sheet, an aluminum-zinc alloy plated steel sheet, a zinc-aluminum-magnesium alloy plated steel sheet, or the like. Any zinc-based plated steel sheet may be used.

  The organic film 15 may be formed on both sides of the galvanized steel sheet 11 or only on one side. When the organic film 15 is formed only on one side of the galvanized steel sheet 11, a generally known back coating film, thin film organic film, inorganic chemical conversion film, etc. may be formed on the other surface of the galvanized steel sheet 11. . In this case, corrosion of the other surface of the galvanized steel sheet 11 is suppressed. The coefficient of friction of the film (back surface film) formed on the other surface of the galvanized steel sheet 11 is preferably 0.17 or less. In this case, since the slidability at the time of press molding of the organic coated galvanized steel sheet 10 is enhanced, the press moldability of the organic coated galvanized steel sheet 10 is improved.

Example 1
Hereinafter, the details of the test material used in the experiment will be described.

First, the details of the polyester resin used in the experiment will be described.
As a polyester resin, “Byron ^TM 103” which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 47 ° C., number average molecular weight: 23000, hydroxyl value: 5 KOH mg / g [described as B-103 in Table 1) ), “Byron ^TM 630” which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 7 ° C., number average molecular weight: 23000, hydroxyl value: 5 KOH mg / g [denoted as B-630 in Table 1)), “Byron ^TM GK140” (Tg: 20 ° C., number average molecular weight: 13000, hydroxyl value: 10 KOHmg / g [shown as B-GK140 in Table 1]), an amorphous polyester resin manufactured by Toyobo Co., Ltd. “Byron ^TM GK130” (Tg: 15 ° C., number average molecular weight: 7000, hydroxyl value: 19 KOHmg / g [Table 1] Some are described as B-GK130]), “Byron ^TM GK180” which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 0 ° C., number average molecular weight: 10,000, hydroxyl value: 23 KOHmg / g [in Table 1) Is described as B-GK180]), “Byron ^TM 230” which is an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 67 ° C., number average molecular weight: 23000, hydroxyl value: 5 KOH mg / g [B in Table 1) -Byron ^TM 670 ", an amorphous polyester resin manufactured by Toyobo Co., Ltd. (Tg: 7 ° C., number average molecular weight: 30000, hydroxyl value: 2 KOH mg / g or less [in Table 1, B- 670)]).

Since these polyester resins are in the form of pellets or sheets, they are used by dissolving them in an organic solvent (a mixture of cyclohexanone and Solvesso 150 (trade name) at a mass ratio of 1: 1). In addition, “Byron ^TM 103” and “Byron ^TM 230” are mixed at a solid content mass ratio of “B-103: B-230 = 6: 1” to add an organic solvent (cyclohexanone and Solvesso 150 (trade name) 1 1), a polyester resin having a Tg of 50 ° C. and a number average molecular weight of 23000 was prepared (described as blend A in Table 1).

Furthermore, “Byron ^TM 630” and “Byron ^TM GK180” are mixed in a solid mass ratio of “B-630: B-GK180 = 1: 1.3” and mixed with an organic solvent (cyclohexanone and Solvesso 150 (trade name). ) Was dissolved in a mass ratio of 1: 1) to prepare a polyester resin having a Tg of 3 ° C. and a number average molecular weight of about 16000 (described as blend B in Table 1).

Furthermore, “Byron ^TM 130” and “Byron ^TM 630” are mixed at a solid content mass ratio of “B-130: B-630 = 8.3: 1.7” and mixed with an organic solvent (cyclohexanone and Solvesso 150 (product). Name) was dissolved in a mass ratio of 1: 1) to prepare a polyester resin having a Tg of 40 ° C. and a number average molecular weight of about 23,000 (described as blend C in Table 1).

Next, a necessary amount (see Table 1) of “CYMEL ^™ 303” which is a fully alkyl methylated melamine resin manufactured by CYTEC was added as an amino resin to the polyester resin dissolved in the solvent. Furthermore, by adding 0.5% by mass of the catalyst “CYCAT ^™ 600” manufactured by CYTEC as an acidic catalyst to the polyester resin and melamine resin dissolved in the solvent with respect to the solid content (total of polyester resin and melamine resin). A clear paint was prepared.

Next, coloring pigments (black pigment, white pigment, metallic pigment) were added to the clear paint as necessary. Here, in this example, carbon black “Toka Black # 7350 / F” manufactured by Tokai Carbon Co., Ltd. as a black pigment, titanium oxide “Typek ^™ CR-95” manufactured by Ishihara Sangyo Co., Ltd. as a white pigment, and metallic pigments are used. Aluminum flakes manufactured by Toyo Aluminum Co., Ltd. were used.

  At the level colored black, carbon black was added to the clear paint at a ratio of 5 parts by mass with respect to 100 parts by mass of the total resin solid content of the clear paint (total solid content of polyester resin and melamine resin). At the level colored white, titanium oxide was added to the clear paint at a ratio of 100 parts by mass with respect to 100 parts by mass of the total resin solid content of the clear paint (total solid content of polyester resin and melamine resin). At the level colored metallic, aluminum flakes were added to the clear paint at a ratio of 3 parts by mass with respect to 100 parts by mass of the total resin solid content of the clear paint (total solid content of polyester resin and melamine resin). A base paint was prepared by the above treatment.

  Next, polymethyl methacrylate (PMMA) fine particle powder was classified to prepare PMMA beads having maximum particle sizes of 10 μm, 15 μm, 20 μm, 30 μm, 55 μm, and 65 μm. In addition, PS beads having a maximum particle size of 30 μm were prepared by classifying polystyrene (PS) fine particle powder. Then, each bead was added to the base coating material at a ratio of 3 parts by mass with respect to 100 parts by mass of the total solid content of the base coating material (total solid content of polyester resin, melamine resin, and pigment). The beads used in Example 1 all had a glass transition point of 190 ° C. and a melting point of 250 ° C.

  Furthermore, the level which added the microcrystalline wax as needed was also produced. The amount of microcrystalline wax added was the value shown in Table 1 with respect to 100 parts by mass of the total solid content of the base paint (total solid content of the polyester resin, melamine resin and pigment).

  Further, an organic solvent (a mixture of cyclohexanone and Solvesso 150 (trade name) at a mass ratio of 1: 1) was added to the coating material prepared above, so that the total solid content concentration was 30% by mass. Thereby, an organic film paint was produced.

  The produced organic coating material is shown in Table 1.

Next, the chemical conversion treatment liquid (chromate-free chemical conversion treatment liquid) used in the experiment will be described in detail.
An aqueous solution containing a silane coupling agent at a concentration of 5 g / L, water-dispersed fine silica at 1.0 g / L, and an aqueous acrylic resin at a concentration of 25 g / L was prepared, and this aqueous solution was used as a chromate-free chemical conversion treatment solution. Note that γ-glycidoxypropyltrimethoxysilane was used for the silane coupling agent, “Snowtex-N” manufactured by Nissan Chemical Co., Ltd. was used for the fine silica, and polyacrylic acid was used for the water-based acrylic resin.

Next, the test material of the organic-coated zinc-based plated steel sheet used in the experiment will be described in detail.
As galvanized steel plates (original plates), electrogalvanized steel plates (hereinafter referred to as EG) manufactured in an electrogalvanizing line called EGL, hot dip galvanized steel plates (hereinafter referred to as GI) manufactured in a hot dip galvanizing line called CGL ), A Zn-11% Al-3% Mg-0.2% Si alloy-plated steel sheet (hereinafter referred to as ZM) produced by a hot dip galvanizing line called CGL was prepared. The plating adhesion amount of EG was 20 g / m ^{2 on} one side (the same adhesion amount on both surfaces), and the plating adhesion amount on GI and ZM was 60 g / m ^{2 on} one side (the same adhesion amount on both surfaces).

Oil was not applied to the zinc-based plated steel sheet, and the zinc-based plated steel sheet was used as it was. Some of the zinc-plated steel sheets were subjected to chemical conversion treatment. Specifically, the chemical conversion treatment liquid was applied on both surfaces of the zinc-based plated steel sheet with a roll coater so as to adhere to the zinc-based plated steel sheet with a surface density of a total solid content of 200 mg / m ² . Next, the chemical conversion solution was dried in a hot air oven. The set temperature of the hot air oven was set to 60 ° C. as the ultimate plate temperature of the steel plate.

  Next, the organic film paint shown in Table 1 was applied to one surface of all galvanized steel sheets using a curtain coater or a roll coater, and the back film paint was applied to the other surface using a roll coater. Subsequently, each paint was dried (baked) in a hot air oven. Here, the ultimate plate temperature during drying was 230 ° C. The time from the start of drying to the time when the plate temperature reached 230 ° C. was 30 seconds. Water was sprayed on the steel plate after drying, and then the steel plate was water-cooled to obtain a test material. The film thickness (dry film thickness) of the organic film was as shown in Table 2, and the film thickness (dry film thickness) of the back film was 0.8 μm. These film thicknesses were obtained by adjusting the paint discharge flow rate of the curtain coater, the peripheral speed of the roll of the roll coater, the nip pressure between rolls, and the solid content concentration of the paint. The film thickness was measured with an electromagnetic film thickness meter after the galvanized steel sheet was dried.

  Here, a back coating film was prepared by adding the same wax as that used in the organic coating material to “FL100HQ” manufactured by Nippon Fine Coatings Co., Ltd., which is a commercially available polyester-based coating material. The amount of wax added was adjusted so that the friction coefficient μ of the back film was 0.1. The color of the back coating film was clear.

  The prepared specimens (samples) are shown in Table 2.

  Hereinafter, the details of the evaluation method of the prepared organic coated zinc-based plated steel sheet will be described.

I-1. Cross-sectional microscope observation (bead distribution)
An arbitrary place of the prepared sample was cut to a length of 20 mm, and the cross section was embedded in the resin so that the cross section in the length direction could be observed. Thereafter, the cross section of the observation target was polished and observed with an optical microscope. Then, the maximum particle diameter of beads mixed in the cross section of the organic film was measured by microscopic observation, and the number of beads 14 (beads satisfying the condition of φ> 3t) was further measured. The case where one or more beads 14 were mixed in the cross section was evaluated as “G (good)”, and the case where no beads were mixed was evaluated as “B (bad)”.

I-2. Cross-sectional microscope observation (film thickness)
An arbitrary place of the prepared sample was cut to a length of 20 mm, and the cross section was embedded in the resin so that the cross section in the length direction could be observed. Thereafter, the cross section of the observation target was polished and observed with an optical microscope. And the film thickness of the organic membrane | film | coat which covers each bead was measured. As a result, the film thicknesses of Invention Examples 1 to 6, 10 to 15, 19 to 28, 33 to 35, 38 to 39, 41 to 42, and 49 to 61 were values within a range of 0.1 μm or more. It was.

II. Measurement of Coefficient of Friction on Film Surface Using TRIBOGEAR TYPE: FW manufactured by HEIDON, a stainless sphere was pressed against the film surface of the sample with a load of 100 g. In this state, the dynamic friction coefficient when the sample was moved was measured.

III. Drawing The sample was subjected to a cylindrical drawing test using an Erichsen type 20t press tester. The die shoulder R of the mold was 3 mm, the punch shoulder R was 3 mm, and the punch diameter was φ50 mm. And the cup-shaped molded object was obtained by pressing until it squeezed the sample on the conditions of drawing ratio 2.0, wrinkle pressing pressure 1t, and no lubricating oil. The molded body was immersed in boiling water for 1 hour, and the state of film peeling and cracking after immersion was observed.

  A sample in which the film is not peeled off at all, or a sample in which no crack is observed even when observed with a 10 × magnifier, is “VG (very good)”, a sample whose film peeling width from the end face of the molded product is within 2 mm, or a 10 × magnifier “G (good)” is a sample in which cracks are observed in the sample, “P (poor)” is a sample in which the film peeling width from the end surface of the molded product is 5 mm or less, or samples in which minute cracks are visually observed. A sample having a film peeling width of more than 5 mm from the end face or a sample in which remarkable cracks were observed visually was evaluated as “B (bad)”.

IV. Flat plate sliding test The damage state of the organic film when the sample was pressed with a press mold containing a large number of wrinkles was evaluated by the following flat plate sliding test. Specifically, as shown in FIG. 3, a specimen (sample) 31 cut into a strip shape having a width of 30 mm is sandwiched between two molds (die pairs) 32, and pressed pressure (P): The mold 32 was pressed against the test material 31. In this state, the specimen 13 was pulled out in the direction of arrow A. And the surface state of the specimen 31 was observed. The flat plate sliding test was performed using two types of mold pairs 32 having different roughness of the surface 32a in contact with the specimen 31. One mold pair 32 has a surface 32a mirror-finished (specifically, Ra of the surface 32a is less than 0.1 μm). The flat plate sliding test using this mold pair 32 is a reproduction test of the operation of pressing the organic-coated zinc-based plated steel sheet 10 with a mold without wrinkles. In the other mold pair 32, the surface 32a is finished with high roughness (specifically, Ra of the surface 32a is 0.2 to 0.3 μm). The flat plate sliding test using this mold pair 32 is a reproduction test of an operation in which the organic-coated zinc-based plated steel sheet 10 is pressed with a mold containing rivets.

  The observed surface is a surface (surface) coated with an organic film. When the organic film is not damaged at all, “VG (very good)” is used, and when the film contains linear streaks. The evaluation was “G (good)”, “P (poor)” when the film was partially peeled, and “B (bad)” when the film was completely peeled off.

V. Corrosion resistance test A sample for a corrosion resistance test was prepared by cutting the sample into a size of 70 mm in width and 150 mm in length and sealing the whole end face portion with tape. And the salt spray test was implemented by the method as described in JISZ2371. The salt water was sprayed on the surface (surface) having the organic film. The test time was 72 hours.

  After completion of the test, the rust generation area ratio of the surface having the organic film (surface) is evaluated. A rust generation area ratio of 0% is “VG (very good)” and a rust generation area ratio of 5% or less is “G (good)”. ”, 10% or less was evaluated as“ P (poor) ”, and 10% or more was evaluated as“ B (bad) ”.

VI. Post-paint appearance evaluation The paint appearance of the samples was evaluated. Specifically, a sample having no unpainted portion due to partial non-formation of paint curtain (such unpainted portion is generally called a curtain spot) and having a beautiful uneven appearance is designated as “VG (very good)”. ) ”,“ G (good) ”is a sample in which a minute curtain spot or armpit appearance that is difficult to visually confirm is generated, and a sample (part) in which a curtain spot or armpit appearance that is clearly recognized visually (P (poor)), a sample that could not be curtain-painted because the paint did not form a paint curtain, and the appearance of the whole surface was generated. The sample was evaluated as “B (bad)”.

Details of the evaluation results will be described below.
Table 2 shows the evaluation test results.

  The organic films of Invention Examples 1 to 6, 10 to 15, 19 to 35, 38 to 39, 41 to 42, and 49 to 61 include beads that satisfy the condition of φ> 3t. For this reason, even if these invention examples are press-molded using a high-roughness mold, wrinkles and the like are unlikely to enter the organic film. That is, these inventive examples were excellent in press formability.

  When Comparative Examples -7 to 9, 16 to 18, 36, 37, 40, and 43 to 48 in which φ was 3 t or less were press-molded using a high roughness mold, wrinkles were likely to enter the organic film.

  Invention examples in which one or more beads satisfying the condition of φ> 3t were found when observing an arbitrary cross section having a length of 20 mm (Invention Examples-1 to 6, 10 to 15, 19 to 35, 38, 39, 41, 42, 49 to 61) were press-molded using a high-roughness mold, and it was difficult for wrinkles or the like to enter the organic film. Therefore, these invention examples were excellent in press moldability.

  Furthermore, in the present invention examples 1 to 6, 10 to 15, 19 to 35, 38 to 39, 41 to 42, and 49 to 61, the film thickness of the organic film covering the beads is a value within a range of 0.1 μm or more. there were. Therefore, also in this respect, the examples of the present invention were excellent in press formability.

  In the invention example in which the film thickness of the organic film is 3 to 20 μm, suitable results were obtained. In the example in which the film thickness exceeds 20 μm (Invention Example 57), the appearance defect due to the outer appearance slightly occurred.

  In the present invention example, even if the organic film contains a coloring pigment in addition to the beads (Invention Examples-10-15, 19-24, 26, 28, 30, 32, 34, 35, 38, 39, 42, 50, 52-61), good results were obtained. When a color pigment is included, designability can be imparted. For this reason, it is preferable to add a coloring pigment in addition to the beads in the organic film.

  When the example of the invention in which the friction coefficient of the organic film was μ ≦ 0.17 was press-molded using a high roughness mold, wrinkles and the like were difficult to enter the organic film. For this reason, these invention examples were excellent in press moldability. In the invention example of μ> 0.17 (Invention Example-24), wrinkles and the like were more likely to enter the organic film than in the invention example of μ ≦ 0.17.

  The main resin of the organic film is composed of 100 parts by mass of a polyester resin having a number average molecular weight of 13,000 to 30,000, a hydroxyl value of 10 KOHmg / g or less, and a Tg of 3 to 50 ° C., and 15 to 30 parts by mass of an amino resin. In the invention examples, more favorable results were obtained. More specifically, suitable results were obtained when the glass transition point of the main resin of the organic film was 3 to 20 ° C, 3 to 10 ° C, or 40 to 50 ° C. Furthermore, more favorable results were obtained when the hydroxyl value was 5 KOH mg / g or less.

  When curtain coating is performed using an organic film coating material in which the number average molecular weight of the polyester resin is less than 13,000, Tg is less than 3, and the hydroxyl value exceeds 10 KOHmg / g, the formation of the paint curtain becomes unstable. For this reason, there was a tendency for curtain coating to become difficult (Invention Examples -29 to 32). Moreover, when the said organic membrane coating material was applied to the zinc-based plated steel sheet with a roll coater (Comparative Examples −45 to 48), it was difficult to mix beads satisfying the condition of φ> 3t in the organic membrane. .

  A polyester resin having a polyester resin with a number average molecular weight exceeding 30,000 could not be confirmed in this experiment because it was difficult to obtain as a coating resin. However, even if such a polyester resin can be obtained, the organic coating material containing the polyester resin has a high viscosity, and it is expected that curtain coating using the organic coating material is difficult.

  When an example of the invention in which the Tg of the polyester resin exceeds 50 ° C. (Invention Example-33, 34) is press-molded using a high-roughness mold, the polyester resin has a Tg of 50 ° C. or lower than that of the invention example. It was easy to get wrinkles in the film. Invention Examples (Invention Examples 5 and 14) in which the amino resin is less than 15 parts by mass, and Invention Examples (Invention Examples 4 and 13) in which the amino resin exceeds 30 parts by mass are used in a high roughness mold. In the case of press molding, wrinkles or the like tended to easily enter the organic film as compared with the invention examples in which the amino resin content was 15 to 30 parts by mass.

  When the inventive example in which the chemical conversion treatment was performed between the zinc-based plating layer and the organic film was press-molded using a high-roughness mold, it was difficult for wrinkles or the like to enter the organic film. Therefore, these invention examples were excellent in press moldability. Inventive examples that were not subjected to chemical conversion treatment (Invention Examples-41, 42) were pressed under the same conditions except that they were subjected to chemical conversion treatment when they were press-molded using a high roughness mold ( It was easier for wrinkles or the like to enter the organic film than Invention Examples-1 and 10).

  When an organic film paint containing beads is curtain-coated on a zinc-based plated steel sheet, beads satisfying the condition of φ> 3t are mixed in the organic film. Therefore, even when the organic coated zinc-based plated steel sheet produced by this method, that is, the present invention example was press-molded using a high roughness mold, wrinkles did not easily enter the organic film. Therefore, the examples of the present invention were excellent in press formability. On the other hand, in the organic coated zinc-based plated steel sheet (Comparative Examples-43 to 48) produced using a roll coater, beads satisfying the condition of φ> 3t are not mixed in the organic film. For this reason, these organic-coated zinc-based plated steel sheets tended to be inferior in press formability.

  When the above test was performed by changing the original plate to an electrogalvanized steel sheet, a hot dip galvanized steel sheet, and a Zn-11% Al-3% Mg-0.2% Si alloy-plated steel sheet, the same results as the above test were obtained. It was.

(Example 2)
Next, Example 2 was performed in order to investigate the correlation between the glass transition point of the beads and the scratch resistance of the organic-coated zinc-based plated steel sheet. Specifically, the beads used in Example 1 of the present invention described above were changed to beads having glass transition points of 200 ° C., 170 ° C., 155 ° C., 150 ° C., and 140 ° C. (melting points were all 250 ° C.) The sample material was produced by the same method as the production method of Invention Example 1. These beads are made of polymethyl methacrylate (PMMA) fine particle powder having a glass transition point of 200 ° C., 170 ° C., 155 ° C., 150 ° C., and 140 ° C., and the maximum particle size is the same as in Example 1 of the present invention. It was obtained by classifying as follows.

  And the flat plate sliding test mentioned above was done with respect to each test material. According to this result and the result of Example 1 of the present invention, when the glass transition point was 170 to 190 ° C., the coating was not damaged at all. On the other hand, when the glass transition point was 200 ° C. and 155 ° C., the film was slightly damaged. When the glass transition points were 150 ° C. and 140 ° C., many damages were observed in the coating. Therefore, it was found that the scratch resistance of the organic-coated zinc-based plated steel sheet is further improved when the glass transition point of the beads is higher than 150 ° C. and the melting point is 250 ° C. or higher. It was also found that the glass transition point is more preferably 170 to 190 ° C.

Example 3
Next, Example 3 was performed in order to investigate the correlation between the bead distribution and the scratch resistance of the organic-coated zinc-based plated steel sheet. Specifically, in a cross section having a length of 20 mm, the total number of beads is 10 or more, and beads satisfying the condition of φ> 3t are 1.0%, 5.0% with respect to the total number of beads in the cross section. The sample material was prepared by the same method as the manufacturing method of Example 1 of the present invention except that the bead distribution was adjusted to be 0.5% and 0.5%. And the flat plate sliding test mentioned above was done with respect to each test material. However, Ra = 0.5 of the mold was set. As a result, when the abundance ratio of beads was 1.0% and 5.0%, no damage was observed in the film. On the other hand, when the abundance ratio of the beads was 0.5%, the film was slightly damaged. Therefore, in a cross section having a length of 20 mm, the total number of beads is 10 or more, and the bead satisfying the condition of φ> 3t is 1.0% or more with respect to the total number of beads in the cross section. It was found that the scratch resistance of the coated galvanized steel sheet was further improved.

Claims (9)

In a steel sheet in which an organic coating containing beads is coated on at least one side of the zinc-based plating layer, the organic coating has a particle size satisfying the condition of φ> 3t, where t is the film thickness and φ is the particle size of the beads. Including beads,
The glass transition point of the resin constituting the beads rather greater than 0.99 ° C.,
An organic-coated galvanized steel sheet comprising at least one bead satisfying a condition of φ> 3t when an arbitrary cross section having a length of 20 mm is observed . The beads are characterized by being covered with the organic film, according to claim 1 the organic coating galvanized steel sheet according. The organic coating zinc-based plated steel sheet according to claim 1 or 2 , wherein the organic film has a thickness of 3 to 20 µm. The organic-coated zinc-based plated steel sheet according to any one of claims 1 to 3 , wherein the organic film contains a color pigment in addition to the beads. The main resin of the organic film consists of 100 parts by mass of a polyester resin having a number average molecular weight of 13,000 to 30,000, a hydroxyl value of 10 KOHmg / g or less, and a glass transition point of 3 to 50 ° C., and 15 to 30 parts by mass of an amino resin. The organic-coated zinc-based plated steel sheet according to any one of claims 1 to 4 , wherein: The organic-coated zinc-based plated steel sheet according to claim 5 , wherein the polyester resin has a glass transition point of 3 to 20 ° C. The organic coated zinc-based plated steel sheet according to claim 5 or 6 , wherein the polyester resin has a hydroxyl value of 5 KOHmg / g or less. The organic coated zinc-based plated steel sheet according to any one of claims 1 to 7 , wherein a chemical conversion treatment is performed between the zinc-based plating layer and the organic film. By applying a paint containing beads on a zinc-plated steel sheet with a curtain coater and then performing dry baking, grains that satisfy the condition of φ> 3t when the film thickness of the organic film is t and the particle size of the beads is φ. wherein the diameters of the beads, the glass transition point of the resin constituting the beads rather greater than 0.99 ° C., when observed any cross-sectional length 20 mm, phi> organic film containing one or more conditions are satisfied beads 3t Production method for obtaining an organic-coated zinc-based plated steel sheet coated with bismuth.