JP2005028822A - Coated steel sheet containing no chromium - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a coated steel sheet containing no chromium which shows excellent corrosion resistance, processability and coat adhesion and excels particularly in the corrosion resistance of a marred portion and a cut end face portion, without using a chromate substrate treatment or a chromate rustproof pigment. <P>SOLUTION: In the coated steel sheet prepared by forming an undercoat and a topcoat on a zinc-plated or aluminum-plated steel sheet subjected to a zinc phosphate treatment or a substrate treatment with non-chromium such as silica, the undercoat is made to contain at least one kind of rustproof pigment selected from orthophosphate and the silica and containing no chromium, and a crystalline resin beads of 1-20 mass%. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a coated steel sheet not containing chromium. The coated steel sheet of the present invention is suitable for various home appliances such as lighting fixtures, refrigerators, washing machines, heating appliances, and air conditioner outdoor units. Also, it can be applied for building materials.

  Pre-coated steel sheets (pre-coated steel sheets) are widely used in home appliances and building materials because of their excellent productivity. The coated steel sheet is required to have excellent workability in addition to corrosion resistance.

  Conventional general coated steel sheets are coated chromate treatment as a base treatment on plated steel sheets, followed by an undercoat containing chromate-type anticorrosive pigments such as strontium chromate and zinc chromate, and then overcoating It has been manufactured by painting a paint. The combined effect of the chromate treatment and the undercoating film containing the chromate-type anticorrosive pigment results in a coated steel sheet having excellent corrosion resistance and excellent workability and coating film adhesion.

  However, due to recent heightened awareness of environmental issues, the use of harmful heavy metals such as chromium in coated steel sheets is being banned, particularly in Western Europe. For this reason, there is an increasing need for a coated steel sheet that does not use chromium for both ground treatment and painting, and does not contain chromium.

  As such a coated steel sheet, for example, in Patent Document 1, a non-chromium coating film in which porous silica containing calcium ions by ion exchange and polyphosphate are contained as non-chromic rust preventive pigments is formed. Based steel sheet has been proposed.

  Patent Document 2 discloses a coated steel sheet in which a coating film containing silica having calcium ions adsorbed on both surfaces of the steel sheet is formed.

  In addition, as described in these patent documents, several base treatment methods other than chromate, such as phosphate-based and silica-based, have been developed.

However, the coated steel sheet having the coating film disclosed in the above patent document cannot achieve both sufficient corrosion resistance, coating film adhesion and workability. That is, when non-chromium rust preventive pigments such as porous silica and polyphosphate are added in an amount within a range in which workability is good, the corrosion resistance of scratches and cut end faces becomes insufficient. Increasing the amount of the non-chromium-based rust preventive pigment improves the corrosion resistance to some extent, but then the workability is significantly reduced.
JP 2001-212506 A Japanese Patent Laid-Open No. 2001-247980

  The present invention shows good corrosion resistance, workability, and coating film adhesion without using a chromium-based ground treatment or a chromium-based anticorrosive pigment, and is particularly excellent in corrosion resistance at scratches and cut end surfaces. It is an object of the present invention to provide a coated steel sheet that does not include.

  When the present inventors added crystalline resin beads to the coating film of a coated steel sheet using a non-chromium-based anticorrosive pigment as disclosed in the above patent document, the scratched or cut part of the coated steel sheet It has been found that the corrosion resistance is remarkably improved. And the fall of workability can be suppressed compared with the method of increasing the addition amount of a rust preventive pigment and improving corrosion resistance.

  Here, the present invention relates to a coated steel plate not containing chromium having one or more coating layers on at least one side of a plated steel plate, wherein at least one coating layer comprises (a) a phosphate and a metal cation. It is a coated steel sheet characterized by containing at least one rust-preventing pigment not containing chromium and (b) crystalline resin beads selected from contained silica.

  In a preferred embodiment, the at least one coating layer contains 1 to 20% by mass of crystalline resin beads. Preferably, the coated steel sheet has two or more coating layers, and the at least one coating layer is a coating layer other than the outermost layer. It is preferable that the plated steel sheet has been subjected to non-chromium base treatment.

  The coated steel sheet according to the present invention has good corrosion resistance, coating film adhesion, and workability even in the absence of chromium, which is considered to be an environmental problem, and is also good at scratches and cut end surfaces. Corrosion resistance can be ensured. The product using this coated steel plate is estimated to have a longer useful life than before.

  The plated steel sheet used as a base material in the coated steel sheet according to the present invention is preferably a zinc-based or aluminum-based plated steel sheet having excellent corrosion resistance. The plated steel sheet may be, for example, an electroplated steel sheet such as an electrogalvanized steel sheet or an electrozinc alloy plated steel sheet (for example, an electro-Zn-Ni alloy-plated steel sheet). In general, hot dip galvanized steel sheets, alloyed hot dip galvanized steel sheets, hot dip galvanized steel sheets, hot dip galvanized steel sheets, hot 55% Al—Zn alloy galvanized steel sheets, etc. are generally used.

  The plated steel sheet of the base material is preferably subjected to non-chromium base treatment in order to improve corrosion resistance and coating film adhesion. Examples of such ground treatment include, but are not limited to, zinc phosphate treatment and silica-based ground treatment. For example, zirconium-based, titanium-based or other metal-based substrate treatment is also possible. The ground treatment is preferably formed by coating and drying from the viewpoint of operation.

  Thus, preferably, at least one coating layer containing a chromium-free rust preventive pigment (hereinafter referred to as non-chromium-based rust preventive pigment) and crystalline resin beads according to the present invention is provided on at least one surface of the plated steel sheet that has been subjected to the ground treatment. 1 or 2 or more coating film layers are formed.

  When the above-mentioned one or two or more coating layers are formed only on one surface of the plated steel sheet, the surface is usually directed to the outer surface of the product because it has excellent corrosion resistance. The opposite surface (hereinafter referred to as the back surface) may be left as plated, or may be left as plated + undercoat, or a coated surface on which one or more coating layers other than the present invention and / or the present invention are formed. It is good.

  As described above, a general coated steel sheet is manufactured by forming two coat layers of an undercoat and a top coat on a plated steel sheet that has been subjected to a base treatment, and the rust preventive pigment is contained in the undercoat coat layer. Similarly, also in the present invention, two layers in which a coating layer containing a non-chromium-based anticorrosive pigment and crystalline resin beads is used as an undercoat and an overcoat coating layer containing no antirust pigment is formed thereon. It is preferable to use a coating film.

  However, the configuration of the coating layer is not limited to the two-layer coating described above. For example, the coating layer can be a single coating layer containing a non-chromium anticorrosive pigment and crystalline resin beads, or three or more coating layers can be formed. It is. When two or more coating layers are provided, the coating layer containing the non-chromium rust preventive pigment and the crystalline resin beads is preferably arranged other than the outermost layer. For example, in the case of a three-layer coating of inner layer, middle layer, and outer layer, such a coating layer is preferably disposed in the inner layer or the middle layer, or in both the inner layer and the middle layer. Below, the case of the preferable two-layer coating film mentioned above is demonstrated.

  The base resin of the undercoat coating layer and the top coating layer is not particularly limited as long as it is suitable for the coated steel plate. Preferred is a resin selected from epoxy, polyester, and urethane. It is preferable to form a coating film in which the base resin is thermally cured by coexisting one or more of melamine resin, polyisocyanate, polyamine, and phenol resin as a curing agent in the paint. The paint may be a solvent-based paint obtained by dissolving a resin in an organic solvent.

  In addition to the base resin and the curing agent, the undercoating material comprises (a) at least one rust-preventing pigment not containing chromium selected from phosphate and silica, and (b) crystalline resin beads in accordance with the present invention. Add. By adding the crystalline resin beads together, the corrosion resistance of the coated steel sheet can be remarkably improved while maintaining good processability as compared with the case where only the non-chromium rust preventive pigment is added. As a result of the addition of the crystalline resin beads suppressing the amount of moisture that permeates the coating film, it is presumed that the adhesion of the coating film in a wet state could be improved.

  Examples of the phosphate used as the rust preventive pigment include magnesium phosphate, calcium phosphate, and aluminum polyphosphate.

  In the case where the rust preventive pigment is silica alone, the silica is preferably a silica in which a metal cation such as calcium, zinc, cobalt, lead, strontium, and barium is contained in porous silica by ion exchange. This is because such a metal cation-containing silica has a higher effect of improving the corrosion resistance of the coating film than silica containing no metal cation. Of these, porous silica containing calcium ions (also called calcium silicate) is more preferable in terms of corrosion resistance.

  When the rust preventive pigment contains both phosphate and silica, the silica may be porous silica containing the above metal cation, but may also be silica that does not contain a metal cation, such as dry silica. In the present invention, since such silica also contributes to the improvement of rust prevention, it is considered to be a kind of rust prevention pigment. However, when the rust preventive pigment is silica alone containing no metal cation, the corrosion resistance is improved, but the degree of improvement is slightly reduced.

  The blending amount of the non-chromium rust preventive pigment is preferably 10 to 100 parts by mass with respect to 100 parts by mass of the resin (total solid content of the base resin and the curing agent). If the amount added is too small, the effect of improving the corrosion resistance is small, and if it is too large, the workability as a coated steel sheet is lowered. A more preferable amount is 15 to 50 parts by mass.

  The rust preventive pigment preferably has an average particle diameter of 20 μm or less. If the particle size is too large, the workability is lowered. The finer the particle size, the better the processability, but the cost for grinding the anticorrosive pigment increases and the economic efficiency decreases.

  The crystalline resin beads are spherical granular crystalline resins that are generally obtained by suspension polymerization. The resin type of the crystalline resin beads is preferably polyester, polyethylene, polyamide or the like. The particle size of the beads is preferably in the range of 10-100 μm. When the particle size is smaller than 10 μm, the storage stability of the paint is lowered, and when it is larger than 100 μm, the paintability when the paint is roll coated is lowered.

  The content of the crystalline resin beads in the undercoat paint is 1 to 20% by mass relative to the total solid content of the paint so that a coating film containing 1 to 20% by mass of the beads is formed. If the content of the crystalline resin beads is too small, the effect of improving the corrosion resistance is small, and if it is excessive, the processability is lowered. This content is more preferably 2 to 15% by mass, and even more preferably 5 to 10% by mass.

  A colored undercoat film may be formed by adding an appropriate color pigment to the undercoat paint. In the case where only one coating layer is formed, since only this primer coating is applied, it is preferable to contain a coloring pigment so as to form a coating film colored in a desired color. The color pigment may be either an inorganic rust preventive pigment or an organic rust preventive pigment, and of course, two or more kinds may be mixed.

  An undercoat paint is preferably applied to at least one surface of a ground-treated plated steel sheet, and the paint film is dried by heating to form an undercoat paint film layer containing a non-chromium rust preventive pigment and crystalline resin beads. The thickness of the undercoat coating film layer is preferably in the range of 3 to 30 μm. If it is less than 3 μm, the corrosion resistance is inferior, and if it is 30 μm or more, the economy tends to be inferior.

  The top coating is usually a colored coating containing a color pigment. The base resin and the color pigment are as described above.

  The top coating usually does not contain (a) non-chromium anticorrosive pigments or (b) crystalline resin beads added to the undercoat, but may contain one or both of them. When coated steel sheets are applied to household electrical appliances that are used outdoors (e.g., air conditioner outdoor units), UV absorbers or other weather resistance enhancing additives are added to the top coating to improve the weather resistance of the coating film. May be added.

  When a top coat is applied on the undercoat coating layer and the coating is dried by heating to form the top coat layer, the coated steel sheet of the present invention is obtained. The film thickness of the top coat layer is preferably in the range of 10 to 30 μm.

  The coating may be performed by any appropriate method such as roll coating, curtain flow coating, air spray, airless spray, and the like. The baking conditions are selected so that the resin is sufficiently cured according to the resin type and the curing agent.

  The coated steel sheet of the present invention exhibits good corrosion resistance, workability, and coating film adhesion, and is particularly excellent in corrosion resistance at scratches and cut end surfaces. Therefore, the useful life of the product manufactured from this coated steel sheet is increased.

<Preparation method of painted steel plate>
A hot-dip galvanized steel sheet (the amount of zinc adhered was 60 g / m ² per side, the steel sheet thickness was 0.5 mm) was used as the substrate. Silica-based non-chromium coating type surface treatment (Nippon Paint Surf Coat EC 2000) is bar coated on both sides of this plated steel sheet to achieve an adhesion amount of 300 mg / m ² , and the maximum temperature of the steel sheet is reached. Was dried by heating to 100 ° C.

  Undercoating is applied to one side of the surface-treated plated steel sheet by bar coating so that the dry film thickness is 10 μm, and the coating film is dried by heating in a hot air oven for 45 seconds so that the maximum temperature of the steel sheet reaches 210 ° C. To form an undercoat coating film layer.

  The undercoat used was Toyobo's Byron 29CS (polyester-dissolved product, base resin) and Mitsui Cyanamid-made Cymel 370 (melamine-dissolved product, curing agent) mixed so that the mass ratio in terms of solid content was 85/15. After adding non-chromium anticorrosive pigment (phosphate and / or silica) and crystalline resin beads (polyester, average particle size 50 μm) in the proportions shown in Table 1, using a paint shaker, the antirust pigment and beads Was prepared by dispersing.

  The rust preventive pigment used is as follows.

A: Aluminum polyphosphate (average particle size 10 μm),
B: Magnesium phosphate (average particle size 8 μm),
C: calcium phosphate (average particle size 5 μm),
D: Silica (dry silica, average particle size 10 μm).

  On top of the above undercoat paint layer, the top coat is bar-coated so that the dry film thickness is 15 μm, and the paint film is dried by heating in a hot air oven for 60 seconds so that the maximum temperature of the steel sheet is 235 ° C. The top coat film layer was formed, and a coated steel sheet having a two-layer paint film layer formed on one side was obtained.

  The top coat used was Toyobo's Byron 23CS (polyester-dissolved product, base resin) and Mitsui Cyanamid-made Cymel 303 (melamine-dissolved product, curing agent) mixed so that the mass ratio in terms of solid content was 85/15. By adding and dispersing titanium dioxide (white rust preventive pigment) so that the concentration in the coating film is 40% by mass, and adding 0.5% by mass of p-toluenesulfonic acid as a reaction catalyst to the resin solid content Prepared.

<Evaluation method of coated steel plate>
Corrosion resistance:
About the specimen of the coated steel sheet obtained, salt spray test (JIS Z 2371, 120 hours) and combined cycle test (scratched part (cross cut part) and cut end face part (shear cut, upper burr part)) JASO 60 cycles) and the corrosion resistance was evaluated by the swollen width of the coating film. An upper burr | flash part means the return part of the test material cut | disconnected shear so that a return may come to a coating surface. The combined cycle test consists of salt spray 2 hours → dry (40 ° C.) 4 hours → wet (60 ° C., 98% RH) 2 hours.

  Workability: Evaluated by the minimum number of sheets sandwiched (T-bend) when the coated surface of the test coated steel sheet was placed outside and n sheets of coated steel sheets with the same thickness were sandwiched and bent 180 ° closely. .

  The above test results are shown together in Table 1 together with the type and content of rust preventive pigment in the undercoat coating film (mass% relative to the resin) and the content of crystalline resin beads (mass% in the coating film).

表１からわかるように、塗膜が非クロム系防錆顔料を含有する塗装鋼板において、塗膜に非クロム系防錆顔料と一緒に結晶質樹脂ビーズをを含有させることにより、良好な加工性を保持しつつ、特に傷部および切断端面部の耐食性を著しく改善することができる。この改善は、樹脂ビーズの添加量が５％から10％に増えると、より顕著となる。

As can be seen from Table 1, in a coated steel sheet in which the coating film contains a non-chromium rust preventive pigment, good workability can be obtained by incorporating the crystalline resin beads together with the non-chromium rust preventive pigment in the paint film. In particular, the corrosion resistance of the scratched part and the cut end face part can be remarkably improved. This improvement becomes more remarkable when the amount of resin beads added is increased from 5% to 10%.

  As in the comparative example of Test No. 10, the corrosion resistance is also improved to some extent by increasing the content of the rust preventive pigment, but in that case, the workability is lowered to 2T. Even in this case, when the crystalline resin beads are added according to the present invention, the corrosion resistance is further improved and the workability is also improved. That is, the crystalline resin beads exhibit not only the corrosion resistance but also the effect of improving the workability depending on the case.

Claims (4)

A coated steel sheet having one or two or more coating layers on at least one side of a plated steel plate, wherein none of the coating layers contains chrome, wherein at least one coating layer comprises (a) phosphate and silica A coated steel sheet comprising at least one rust-free pigment containing no chromium, and (b) crystalline resin beads. The coated steel sheet according to claim 1, wherein the at least one coating layer contains 1 to 20% by mass of crystalline resin beads. The coated steel plate according to claim 1 or 2, wherein the coated steel plate has two or more coating layers, and the at least one coating layer is a coating layer other than the outermost layer. The coated steel sheet according to any one of claims 1 to 3, wherein the plated steel sheet has been subjected to a non-chromium base treatment.