JPH04282242A - Coated steel sheet with high corrosion inhibitive properties on end surface - Google Patents

Abstract

PURPOSE:To improve end surface corrosion inhibitive properties significantly by maintaining other coat physical properties such as working properties and resistance against adhesion to boiling water at high level. CONSTITUTION:A coated steel sheet with excellent end surface corrosion inhibitive properties consists of a zinc phosphate and/or chromate forming treated layer 3, a primer coated layer 4 and an organic resin coated layer 5 formed sequentially on the plated surface 2 of a galvanized steel sheet. The primer coated layer consists of scattered small segmented areas which are thinner than the primer coated layer and contains a high concentration of 10wt.% or higher of rust-proof pigment in the continuous phase of a primer coat containing 10wt.% of rust-proof pigment.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a coated steel sheet with excellent rust prevention properties, which is useful for home appliances and building materials, and particularly suitable for outdoor applications where high rust prevention properties are required. The coated steel sheet of the present invention may also be used as an outer panel for automobiles in the future.

0002

BACKGROUND OF THE INVENTION In recent years, demand has been increasing for zinc-based coated steel sheets, ie, coated steel sheets for utensils whose base material is pure galvanized steel sheets or zinc alloy-plated steel sheets. Such coated steel sheets are manufactured by applying one or both of zinc phosphate-based and chromate-based chemical conversion treatments to a zinc-based plated steel sheet as a base material, and then applying a primer paint and then a top coat paint. By using a pre-painted steel plate, the customer can omit a complicated painting process. Due to this advantage, the use of painted steel sheets has become well worth the cost considering the recent rise in labor costs and factory land costs, which is one of the reasons for the increased demand for painted steel sheets. However, coated steel sheets with excellent coating properties have been developed, and furthermore, they can provide high image clarity (smoothness) that is difficult to achieve with post-assembly coating (aftercoat). Improvements in the performance of coated steel sheets are also thought to be contributing significantly to the increase in demand for coated steel sheets.

[0003] Painted steel plates are supplied to consumers in the form of coils or sheets, and the consumers process them into appropriate shapes by cutting or punching for use. The end face of the cut portion varies depending on the steel plate thickness and shear clearance, but the plating and base steel plate are exposed in addition to the coating film. Naturally, the end surface portion is more susceptible to rust than the flat portion with a healthy coating.

[0004] In areas where rusting from the edges poses a problem in terms of appearance, countermeasures have been taken, such as curling or bending the edges, or attaching a plastic frame as seen on refrigerator doors. I've been exposed to it. Although such end face countermeasures are very effective, they require additional steps and changes in design.

[0005] Furthermore, when applying painted steel plates to equipment used outdoors, such as outdoor units of air conditioners, it is necessary to apply primer paint to the primer paint as a measure to suppress rust on the edges and blister rust. Efforts have been made to increase the amount of anti-rust pigments and to increase the thickness of the plating film. However, increasing the amount of anti-rust pigments and increasing the thickness of the plating film tend to reduce the workability of coated steel sheets, and workability is also important for coated steel sheets, so when considering the balance with workability, There is a limit to the improvement of end face corrosion resistance by such measures. Furthermore, the behavior of the corrosion resistance of the coated steel sheet differs depending on the solubility of the antirust pigment. When easily soluble rust preventive pigments (e.g., zinc chromate) are used, the amount of chromic acid eluted from the end face is large, so it shows good corrosion resistance at the initial stage of the corrosion test, but as the test time becomes longer, it rather deteriorates. There are no universal anti-rust pigments, as poorly soluble anti-rust pigments (e.g. barium chromate, strontium chromate) may give better results. Therefore, the current situation is to deal with the problem by appropriately blending different types of anti-rust pigments. Furthermore, if a large amount of anti-rust pigment is blended into the primer paint, the adhesion of the paint film after the boiling water test may be reduced. This tendency is particularly noticeable in the case of easily soluble rust-preventing pigments. As described above, it is difficult to improve the corrosion resistance of the end face without impairing the physical property balance of the coated steel sheet.

[0006] Given the current situation, there is also a technology that guarantees the corrosion resistance of the end face by repairing the cut end face formed after punching or shearing using a simple method of treating it with an alkaline degreasing solution containing a component that forms a rust-preventing film. It has been proposed (Japanese Patent Publication No. 64-289). However, since there is little need to process painted steel sheets using press oil, there is usually no opportunity for alkaline degreasing. Therefore, this treatment requires an additional process on the customer side, and alkaline degreasing is disadvantageous because it risks adversely affecting the performance of the coated steel sheet, such as its stain resistance.

[0007]

[Problems to be Solved by the Invention] The present invention improves the end face corrosion resistance of a coated steel sheet without impairing other physical properties of the coating film (e.g. workability and boiling water resistance), thereby achieving an excellent balance of physical properties of the coating film. The purpose of this project is to provide coated steel sheets that have been coated.

[0008]

[Means for solving the problem] As mentioned above, increasing the content of anti-corrosion pigments in the primer coating film has a remarkable effect on improving the rust-preventing properties on the end faces of coated steel sheets, but it is difficult to improve workability and water-resistant adhesion. decrease. This decrease is due to the fact that the elongation of the coating film decreases when a large amount of anticorrosion pigment is included. The inventors
The primer coating layer containing a large amount of such anti-corrosion pigment is
By dividing it into small sections smaller than the width of cracks that occur during processing, and interspersing them in the primer coating layer,
The present invention was completed by focusing on the ability to prevent the occurrence of cracks during processing.

[0009] Here, the present invention provides, on the plating surface of a zinc-based plated steel sheet, in order from the bottom layer, at least one of a zinc phosphate-based and chromate-based chemical conversion treatment layer, a primer coating layer, and an organic resin coating layer. In the coated steel sheet, the primer coating layer includes small sections that are thinner than the thickness of the coating layer and discontinuous with each other in the primer coating continuous phase containing less than 30% by weight of an anticorrosive pigment. A coating with excellent edge rust prevention properties, characterized in that it is dotted with regions containing a high concentration rust prevention pigment containing a rust prevention pigment of 10% by weight or higher than the continuous layer. It is a steel plate.

0010

[Operation] The present invention will be described in detail below with reference to the accompanying drawings. FIGS. 1(a) and 1(b) are explanatory diagrams schematically showing a cross section of a coated steel plate of the present invention. As shown in this figure, the coated steel sheet of the present invention has a zinc plating layer 2, a chemical conversion treatment layer 3, a primer coating layer 4, and an organic resin, which is the main body of the coating, on a steel sheet base 1, in order from the bottom. It has a coating layer (hereinafter referred to as a top coat layer) 5. The coating layer having such a structure is usually provided on only one side of the plated steel sheet, but it may be provided on both sides in some cases. Further, the top coat layer 5 may be composed of two or more layers, if desired, and may further have a coating layer of a cover coat (eg, clear paint) thereon. Such a structure itself is common for painted steel sheets.

The painted steel sheet of the present invention is characterized in that, as shown in FIG. 1, the primer coating layer 4 has a thickness thinner than that of this layer 4 and contains 10% by weight or more of an anticorrosion pigment. ,
It consists of discontinuous, small-section (eg, spot-like, island-like, granular) high-concentration rust-preventing pigment containing regions (hereinafter abbreviated as high-corrosion-preventing pigment regions) 6 scattered about. The highly antirust pigment areas 6 may be scattered in a regular array on a fixed plane inside the primer coating layer 4, as shown in FIG. 1(a), or may be arranged in a regular arrangement as shown in FIG. 1(b). As shown, they may be randomly scattered in the primer coating layer 4.

[0012] In any case, the rust-preventive pigment is contained in the ordinary primer coating layer 4 which forms the continuous phase (matrix phase) and has a content of the rust-preventive pigment of less than 30% by weight, preferably less than 10% by weight. By discontinuously interspersing highly rust-inhibiting pigment regions 6 containing 10% by weight or more of This can be ensured by However, since the highly rust-preventing pigment area 6 is discontinuous, the coating film does not crack even when processed, and therefore the content of the rust-preventing pigment in this area is as high as 10% by weight or more. However, there is no significant deterioration in processability. In addition, although this discontinuous highly rust-preventing pigment region 6 alone cannot fulfill the original purpose of the primer, a primer coating layer containing less than 10% by weight of the rust-preventing pigment has excellent processability and boiling water resistance. 4 exists as a continuous phase over the entire surface of the steel sheet, the continuous primer layer 4 maintains the coating film adhesion and boiling water resistance required of the primer. As a result, the coated steel sheet of the present invention has a well-balanced combination of various performances such as end face rust prevention, workability, paint film adhesion, and boiling water resistance.

The base material of the coated steel sheet of the present invention is a zinc-based plated steel sheet. The term "zinc-based plated steel sheet" includes pure galvanized steel sheet and various zinc alloy plated steel sheets such as Fe-Zn and Ni-Zn. The zinc-based plated steel sheet may be an electroplated steel sheet, a hot-dip galvanized steel sheet, or an alloyed hot-dip galvanized steel sheet, or may be a multilayer plated steel sheet having two or more plating layers. There is no particular limit to the amount of plating deposited, but as described above, excessive plating thickness has an adverse effect on workability. In addition, in the present invention, the end face rust prevention is ensured by the primer coating layer in which the high rust preventive pigment areas 5 are interspersed, so there is no need to make the plating thickness particularly thick in order to ensure the end face rust prevention. do not have. Therefore, thin film plating is sufficient as long as the thickness is greater than that required to ensure corrosion resistance of the flat plate portion. The preferred amount of plating is 60~60 per side.
It is within the range of 120g/m2.

Adjacent to the plating layer 2, a zinc phosphate chemical conversion treatment layer and/or a chromate treatment layer 3 is provided. This chemical conversion treatment layer 3 is commonly provided on galvanized steel sheets for the purpose of improving corrosion resistance and paint film adhesion, and may be formed in the same manner as before in the coated steel sheet of the present invention. The formation method and the amount of adhesion are not particularly limited.

The discontinuous highly rust-preventive pigment areas 6 dotted in the primer coating layer 4 contain a rust-preventive pigment in order to ensure the end face rust prevention of the coated steel sheet, which is the main objective of the present invention. The content is 10% by weight or more higher than that of the continuous phase, preferably 5% by weight or more higher than the continuous phase. The rust preventive pigment may be either an easily soluble rust preventive pigment (for example, zinc chromate, etc.) or a slightly soluble rust preventive pigment (barium chromate, strontium chromate, etc.), or a combination of both. It's okay.

On the other hand, the continuous matrix phase of the primer coating layer 4 does not contain an anticorrosion pigment, or even if it does, the content thereof is less than 30% by weight, preferably less than 10% by weight. If this continuous phase contains 30% by weight or more of the anticorrosion pigment, the workability and boiling water resistance of the coated steel sheet will decrease. When the highly rust-preventive pigment areas 5 scattered in the primer coating layer 4 contain one type of rust-preventive pigment, the primer coating layer 4 contains 30% of the other type of rust-preventive pigment. Preferably, the content is less than % by weight. In this way, the two types of rust-preventive pigments can be effectively placed in the primer coating, and excellent end-face rust prevention can be guaranteed for a long period of time. Considering the balance with other properties such as processability and boiling water resistance, we added 10% by weight or more of easily soluble rust preventive pigments such as zinc chromate to the scattered high rust preventive pigment areas 6.
Preferably 30% by weight or more, particularly preferably 50% by weight
It is desirable that the continuous primer coating layer 4 contains a hardly soluble rust preventive pigment such as a chromate salt in an amount of less than 30% by weight.

The size of one section (one fragment) of the highly antirust pigment areas 6 scattered in the form of discontinuous small sections may be appropriately selected depending on the required physical properties. In general, it is recommended to prototype a coated steel plate coated with this highly anti-rust pigment area 6 coating on the entire surface, and set the fragment size to be equal to or smaller than the width of the cracks that occur when the coated steel plate is processed. This is desirable from the viewpoint of preventing cracking, that is, improving workability. Therefore, it is preferable that the higher the content of the antirust pigment, the smaller the fragment size of the highly antirust pigment area. Generally, it is preferred that the fragment size (size on a side or diameter) is in the range of 5 to 100 μm.

Similarly, the content of the highly rust-preventing pigment region 6 (the ratio of the cross-sectional area occupied by the highly rust-preventing pigment region 6 to the total cross-sectional area of the primer layer) is also appropriately selected depending on the required physical properties of the coated steel sheet. That is, as this content increases, the end face rust prevention property increases dramatically, but processability and water resistant adhesion tend to decrease. Therefore, an appropriate content rate may be set in consideration of these balances. The normally preferred content range is 10 to 90%.

The thickness of each fragment of the highly antirust pigment area 6 is not particularly limited as long as it is thinner than the thickness of the primer coating layer 4. However, it is not preferable to set the primer coating layer 4 to a thickness that may inhibit the formation of a continuous phase. Furthermore, if the fragment thickness of the highly anticorrosive pigment area 6 becomes too thick, the sharpness of the coated steel sheet will be adversely affected. Therefore, as shown in Figure 1(a),
Even if the highly rust-inhibiting pigment areas 6 are scattered in an orderly arrangement within the primer coating layer 4, in order to maintain high image clarity, the thickness of the highly rust-inhibiting pigment areas 6 must be adjusted in the primer coating layer 4. It is desirable that the thickness be about half or less of the total thickness of the coating phase. Figure 1(b)
), when the highly antirust pigment areas 6 are randomly scattered, it is desirable that the fragment thickness be even smaller.

[0020] The method for manufacturing the coated steel plate of the present invention will be explained next. The coated steel sheet of the present invention having the cross-sectional configuration shown in FIG. 1(a) can be manufactured, for example, as follows. First, a zinc phosphate-based chemical conversion treatment and/or chromate treatment is applied to a base metal plated steel sheet by a conventional method to form a chemical conversion treatment layer 3, and then highly rust-inhibiting pigment areas 6 separated from each other in the form of islands are formed. form. This island-shaped highly rust-preventing pigment area 6 can be produced by flexographic printing, screen printing, etc. using a relatively viscous paint containing a rust-preventing pigment in a conventional primer paint at a solid content of 10% by weight or more. It can be formed by painting in the desired pattern using conventional printing and coating methods. After this paint dries, or without completely drying, a primer paint that does not contain anti-rust pigments or whose content is less than 30% by weight of solids is applied continuously over the entire surface of the steel plate, i.e. in a sea-like manner. to form a primer coating layer 4. This entire surface coating can be carried out by any conventional method, but roll coating or curtain flow coating is practical.

[0021] The resin system used for both the island-like and sea-like primer paints is not particularly limited, and any conventionally used resin such as epoxy, polyester, acrylic, or urethane can be used. system can be used. However, when a high degree of workability is required for the coated steel sheet, it is preferable to use a flexible polyester resin system rather than a hard epoxy resin system.

After drying the primer coating layer 4, a top coat layer 5 is provided by a conventional method. This top coat layer 5 is
It may be formed by a normal coating method using a paint appropriately selected from polyester, urethane, acrylic, and other paints commonly used for coated steel sheets depending on the required physical properties. Thereby, the coated steel plate of the present invention shown in FIG. 1(a) is obtained. If desired, a cover coat layer (eg, clear paint layer) can also be provided on top coat layer 5. The coated steel plate of the present invention having the configuration shown in FIG. 1(b) can be manufactured, for example, by the method described below. By kneading and pulverizing the anti-rust pigment and the resin for primer paint in a ball mill, a granular powder with a particle size of 5 to 100 μm is created by mechanically adsorbing the primer resin on the surface of the anti-rust pigment, and then dispersed in the primer paint. . By applying such a paint onto a steel plate by a normal coating method, it is possible to obtain a coated steel plate as shown in FIG. 1(b) in which highly antirust pigment areas 6 are randomly arranged.

[0023]

EXAMPLES Next, the present invention will be explained in more detail with reference to examples. In the examples, all amounts of paint components are calculated as parts by weight based on the total solid content in the paint. ■Preparation of paint Primer paint: Mix 20 parts of melamine resin (Cymel 325, manufactured by Mitsui Toatsu) with 100 parts of polyester resin (Vylon 29CS, manufactured by Toyobo Co., Ltd.), and add one of the following anti-rust pigments to form glass beads. Disperse the pigment using
Sample primer paints A and B were obtained. The solvent was a 1/1 mixed solvent of cyclohexanone/Solvesso 150. Paint A (highly antirust pigment paint) - Zinchromate 120
Part Paint B (low anti-rust pigment paint) - 10 parts of strontium chromate Paint for top coat: 10 parts of melamine resin (Sumimar M-40S, manufactured by Sumitomo Chemical) per 100 parts of polyester resin (Alumatex HMP25, manufactured by Mitsui Toatsu) and 10 parts of another melamine resin (Cymel 375 manufactured by Mitsui Toatsu Co., Ltd.), and further titanium oxide (Tipaque R82 manufactured by Ishihara Sangyo Co., Ltd.).
0) was used by kneading and dispersing 100 parts with glass beads. The solvent was the same as above.

■Preparation of painted steel plate Hot-dip galvanized steel plate (thickness 0.5
After applying zinc phosphate chemical conversion treatment (1 g/m2) and chromate rinse (5 g/m2 asCr) to form a chemical conversion treatment layer, the primer paint was A (Highly antirust pigment)
A square island-shaped highly anticorrosive pigment area with one side of 50 μm or 500 μm was formed by screen printing using a screen printing method. The island-shaped coating film was applied to a thickness such that the dry film thickness was about 3 μm, and the coverage was adjusted by changing the spacing between the square island-shaped coating films. After the island-like coating film was dry to the touch due to evaporation of the solvent, the primer paint B was applied to the entire surface of the steel plate, that is, in a sea pattern, using a conventional bar coater. The thickness of this sea-like coating film was such that the thickness of the primer layer including the island-like coating film was approximately 8 μm in dry film thickness. The primer coating coated using two types of paints was baked for about 40 seconds to reach a maximum temperature of 210°C, and the resulting image shows islands of highly anti-rust pigment areas regularly scattered. A dried primer coating as shown in 1(a) was obtained. Next, apply the above top coat paint to a dry film thickness of approximately 15 μm.
The coating film was coated using a bar coater so that the coating film had a temperature of 230° C., and was baked for about 70 seconds to reach a maximum temperature of 230° C. to harden the coating film, thereby obtaining a coated steel plate for use as a test sample.

■Evaluation of Corrosion Resistance and Physical Properties of Coating Film Corrosion resistance: Salt spray test of a test piece cut with a shear (shear clearance fixed at the same value) After 600 hours, the maximum blister width of the end face was measured and the corrosion resistance was evaluated. Workability: The workability of the coating film was evaluated using the 180° bending method based on the minimum number of plates that would not cause cracks in the coating film. Image clarity: Evaluated by visual judgment. Boiling water adhesion: A test specimen of a painted steel plate was immersed in boiling water for 2 hours and then taken out. After making 100 cuts of 2mm width to a depth that reached the steel plate base, an Erichsen overhang of 5mm width was made. , cellophane tape was removed. Boiling water resistant adhesion was evaluated based on the number of peeled gobbles. The test results are summarized in Table 1 together with the details of the painted steel plate.

[0026]

[Table 1]

As can be seen from the results in Table 1, Test No. 1, in which the primer coating layer was made only of highly antirust pigment paint, Although No. 6 has very good end face corrosion resistance, the workability and boiling water resistance are extremely poor and it cannot be used for practical use. On the other hand, test No. 1 in which the primer coating layer was made of only a low antirust pigment paint. 7 has excellent processability and boiling water resistance, but
The end face corrosion resistance is extremely poor, and it cannot be used outdoors unless the end face is rust-proofed. On the other hand, the coated steel sheet of the present invention tested no. While maintaining a high degree of workability and boiling water resistance comparable to Test No. 7, the end face corrosion resistance achieved Test No. 7. This has been significantly improved to a level close to 6. The sharpness of all the sample coated steel plates was good, and there was no discernible difference between the inventive example and the comparative example. That is, according to the present invention, even if the highly rust-preventive pigment areas are provided in the primer coating in the form of islands,
There is no substantial negative effect on image sharpness.

[0028]

Effects of the Invention As explained and exemplified above, the coated steel sheet of the present invention has significantly improved end face rust prevention, which was a weak point of conventional coated steel sheets, while maintaining other coating film properties at a high level. can do. As a result, when customers use painted steel plates to manufacture vessels and building materials, there is no need for a rust-proofing process on the end surfaces after cutting, making handling easier.
Manufacturing costs are reduced. Therefore, the painted steel sheet of the present invention is
It is particularly useful for outdoor applications where end face corrosion is severe. Furthermore, if the type of paint and coating method are selected to meet the strict standards required for automobiles, it can also be used for automobile exterior panels.

[Brief explanation of the drawing]

FIGS. 1(a) and 1(b) are explanatory diagrams schematically showing a cross section of a coated steel plate of the present invention.

[Explanation of symbols]

1 Steel plate, 2 Plating layer, 3 Chemical conversion treatment layer, 4 Primer coating layer, 5 Top coat layer, 6 High anti-rust pigment area

Claims (1)

[Claims] Claim 1: A coated steel sheet comprising, in order from the bottom layer, at least one of a zinc phosphate-based and chromate-based chemical conversion treatment layer, a primer coating layer, and an organic resin coating layer on the plated surface of a zinc-based coated steel sheet. In the primer coating layer, the primer coating layer has a rust preventive pigment content of less than 30% by weight in the primer coating continuous phase, which is thinner than the coating layer and has discontinuous small sections. higher concentration than the layer and 1
A coated steel sheet with excellent end face rust prevention, characterized in that it is dotted with regions containing a high concentration rust preventive pigment containing 0% by weight or more of a rust preventive pigment.