JPH0246381B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a plastic film-coated steel plate having an aluminum-zinc alloy plated steel plate as a substrate, the surface of which is coated with a plastic film. BACKGROUND ART Conventionally, plastic film-coated steel plates, which are steel plates or galvanized steel plates coated with plastic film, have been provided as steel plates with improved corrosion resistance. In the case of a galvanized steel sheet whose surface is coated with a plastic film, the surface of the galvanized steel sheet is chemically treated with zinc phosphate or chromic acid, and then plastic is applied to the surface of the chemical conversion layer using an adhesive. It is formed by coating with a film, and the corrosion resistance and weather resistance are improved by galvanizing, chemical conversion treatment, and a film coating layer on the surface. In addition, the adhesives used include chromate rust preventive pigments with chromate ions such as strontium chromate, calcium chromate, barium chromate, and zinc chromate, calcium molybdate, calcium phosphate, aluminum phosphate, and phosphoric acid. Rust-preventing pigments such as titanium, lead cyanamide, calcium leadate, and basic chromic acid are added to the non-volatile content (sum of resin solid content and total pigment) of the adhesive.
By using a 10% by weight compound, the corrosion resistance of galvanized steel sheets is further improved. By the way, it is known that an aluminum-zinc alloy coated steel sheet, in which an aluminum-zinc alloy plating layer is formed on the surface of the steel sheet, has better corrosion resistance than the galvanized steel sheet used above. The zinc-aluminum coated product disclosed in Japanese Patent Publication No. 7161, the corrosion-resistant aluminum-zinc coating and its manufacturing method disclosed in Japanese Patent Publication No. 53-22528, and the corrosion-resistant zinc alloy coated iron metal disclosed in Japanese Patent Publication No. 54-8335. Articles and their manufacturing methods, Tokkosho
According to the iron substrate product having a coating and its manufacturing method disclosed in Japanese Patent Publication No. 56-44143, and the improved method for treating iron strands by hot-dip coating disclosed in Japanese Patent Publication No. 57-11390, aluminum Zinc alloy coated steel sheets are said to have two to six times more corrosion resistance than galvanized steel sheets.
However, when a plastic film-coated steel plate is formed using this aluminum-zinc alloy plated steel plate as a substrate by the above method, the plastic film coated on the surface of the coated steel plate may blister or peel when used in a corrosive atmosphere. The disadvantage is that it occurs from the end face (cut of the coated steel plate).
The blistering and peeling were significantly inferior to those using a galvanized steel plate as a substrate.
The reason why blistering and peeling tend to occur when a plastic film-coated steel sheet is formed using an aluminum-zinc alloy plated steel sheet as a substrate is because the aluminum and zinc in the aluminum-zinc alloy plating layer are not uniformly dispersed, and the aluminum is larger than the zinc. The zinc-rich phase is unevenly distributed between the aluminum-rich phase (aluminum-rich phase) and the aluminum-rich phase (zinc-rich phase). It is thought that the zinc-rich phase corrodes and disappears in preference to the aluminum-rich phase in a corrosive atmosphere, and the resulting hydrogen gas and corrosion products push the plastic film upward. In other words, on the end face of an aluminum-zinc alloy plated steel sheet, batteries are formed by the aluminum-rich phase and the iron on the end face, and the zinc-rich phase and the iron on the end face, and because the potentials of each metal are different, one zinc-rich phase It corrodes first. The present invention has been made in view of the above points, and provides corrosion resistance that prevents the plastic film coated on the surface from peeling off or blistering even when an aluminum-zinc alloy plated steel plate is formed as a substrate. The object is to provide an excellent plastic film coated steel sheet. That is, the present invention provides a chemical conversion treatment layer 3 in which an aluminum-zinc alloy plating layer 1 is chemically treated on the surface of an aluminum-zinc alloy plated steel sheet 2 on which an aluminum-zinc alloy plating layer 1 is formed by hot-dipping. is formed, and at least one of strontium chromate and calcium chromate is added to the surface of this chemical conversion treatment layer 3 in a ratio of 20 to 20% relative to the nonvolatile content of the adhesive.
The above object has been achieved by a plastic film coated steel plate characterized in that it is coated with a plastic film 5 via an adhesive 4 containing 50% by weight. The present invention will be explained in detail below. As shown in the accompanying drawings, an aluminum-zinc alloy plating layer 1 is formed on the surface of a steel plate 8 by a hot-dip galvanizing method. As mentioned above, this aluminum-zinc alloy plating layer (1) is divided into the aluminum-rich phase 6, which contains more aluminum than zinc, and the zinc-rich phase 7, which contains more zinc than aluminum. The rich phase 7 is entangled with the aluminum rich phase 6 like an ant's nest. The components of the aluminum-zinc alloy plating layer 1 are not limited in any way, but for example, Al is 4 to 75% by weight, most of the rest is zinc, and a small amount of third components such as Si, Mg, Ce, and Sn are contained. You can use what you want,Al
-Zn-Si alloy, Al-Zn-Mg alloy, Al-Zn-Ce
It is used for plating alloys, Al-Zn-Sn alloys, etc., and it is particularly preferable to use one containing 55% by weight of Al, 43.4% by weight of Zn, and 1.6% by weight of Si. The surface of this aluminum-zinc alloy plating layer 1 is subjected to a chromic acid-based or zinc phosphate-based chemical conversion treatment to form a chemical conversion treatment layer 3. The chemical conversion treatment can be carried out by spraying, dipping, roll coating, or the like. Next, an adhesive 4 containing strontium chromate or calcium chromate in an amount of 20 to 50% by weight based on the nonvolatile content of the adhesive is applied to the surface of the chemical conversion treatment layer 3 at a rate of 7 to 15 g/m ² (dry state). The plastic film 5 is then coated by baking and drying at a temperature of 180 DEG to 230 DEG C., and then immediately covering the surface of the adhesive 4 with the plastic film 5 and pressing it with a roll or the like. As adhesive 4, acrylic/epoxy type,
Acrylic/phenol type, acrylic/epoxy/
Adhesives such as phenol-based, curable urethane-based, maleic anhydride-modified polypropylene-based, and modified polyester-based adhesives can be used, and in addition to blending the above-mentioned strontium chromate and calcium chromate into these adhesives, titanium oxide Extender pigments such as these and various antirust pigments shown in the conventional examples may be appropriately blended. If the amount of anti-rust pigments such as strontium chromate and calcium chromate is less than 20% by weight based on the non-volatile content of the adhesive 4, the effect of reducing blistering etc. of the film 5 will be small; If it exceeds % by weight, the adhesion to the film 5 will be poor. Further, as the plastic film 5, vinyl chloride film, polymethyl methacrylate film, vinylidene fluoride film, polyester film, polypropylene film, polyethylene film, etc. can be used. These plastic films 5 and the adhesive 4 are used in a corresponding manner to improve adhesiveness. For example, for vinyl chloride film and polymethyl methacrylate film, acrylic/epoxy adhesives and fluoride adhesives are used. Acrylic/phenol/epoxy adhesives are used for vinyl films and vinylidene fluoride films; curable urethane adhesives are used for polyester films; and maleic anhydride-modified polypropylene adhesives are used for polypropylene films and polyethylene films. It is preferable to use In this way, the entire surface of the adhesive 4 is coated with the plastic film 5 to obtain a plastic-coated steel plate. By using the aluminum-zinc alloy plated steel plate 2 as the substrate of this plastic-coated steel plate, the aluminum-zinc alloy plating layer 1 on the surface has higher corrosion resistance than when a conventional galvanized steel plate is used as the substrate. In addition, the plastic film 5 on the surface prevents penetration of water, etc., and improves corrosion resistance, weather resistance, and water resistance. Furthermore, by blending strontium chromate or calcium chromate in an amount of 20 to 50% by weight of the nonvolatile components in the adhesive 4 interposed between the aluminum zinc alloy plated steel sheet 2 and the plastic film 5,
It is possible to prevent corrosion of the aluminum-zinc alloy plating layer 1 and suppress corrosion of the zinc-rich phase 7 of the aluminum-zinc alloy plating layer 1. As described above, the present invention applies an adhesive containing strontium chromate or calcium chromate in an amount of 20 to 50% by weight based on the non-volatile content of the adhesive to the surface of a chemical conversion treatment layer of an aluminum-zinc alloy coated steel sheet. Since the aluminum-zinc alloy plated steel sheet is coated with a plastic film, corrosion resistance can be increased by using the aluminum-zinc alloy plated steel sheet as a substrate, and an adhesive containing a large amount of strontium chromate or calcium chromate can be used to coat the aluminum-zinc alloy plated layer with zinc. It can reduce corrosion of the rich phase and prevent the plastic film on the surface from blistering or peeling even in a corrosive atmosphere. The present invention will be explained in detail below using examples. <Examples 1 to 4, Comparative Examples 1 to 3> Plate thickness 0.4 mm Al55% by weight, Zn43.4% by weight, Si1.6
% by weight of aluminum-zinc alloy plated steel sheet (plating density 150 g/m ² (both sides), plating thickness 20 microns on one side) using Bonderite, a chromic acid-based chemical conversion treatment liquid.
1415A (manufactured by Nippon Parkerizing Co., Ltd.) with a coating amount
Roll coating was carried out to give a coating weight of 150 to 200 mg/m ² (dry state) and dried at 40 to 50°C. Next, on the surface of the formed chemical conversion treatment tank, 20 parts by weight of acrylic copolymer, 9.5 parts by weight of epoxy resin, and 0.5 parts by weight of amine-based curing agent were added.
An adhesive containing strontium chromate in the amount shown in the following table based on the nonvolatile content of an acrylic/epoxy adhesive consisting of 70 parts by weight of methyl isobutyl ketone was added at a rate of 99 to 11 g/m ² (dry state). The plastic film coated steel plate was coated with a polymethyl methacrylate resin film (film thickness 75 microns, manufactured by Kanegafuchi Kagaku Kogyo Co., Ltd.) under roll pressure. I got it. <Examples 5 and 6> A plastic film-coated steel plate was prepared in the same manner as in Example 1, except that an adhesive containing calcium chromate in the amount shown in the following table was used with respect to the nonvolatile content of the acrylic/epoxy adhesive. I got it. <Conventional example> A plastic film-coated steel plate was obtained in the same manner as in Example 1, except that an acrylic/epoxy adhesive containing no anti-rust pigment was applied to the surface of a galvanized iron plate (Z-25) with a thickness of 0.4 mm. . Next, the adhesion of the plastic film-coated steel plates obtained in Examples 1 to 6, Comparative Examples 1 to 3, and the conventional example and the coating film swelling at the end surfaces were measured. In addition,
Evaluation of adhesion and coating blistering on the edge surface was performed as follows. Adhesion - The adhesion of the coating film was evaluated by the cold crosscut Erichsen method and the 80°C hot water crosscut Erichsen method. In the cold cross-cut Erichsen method, cuts are made with a knife in the plastic film on the surface at 5 mm intervals, extruded to 7 mm, and then heated at 135°C.
This is a forced peel test in which one cycle is immersion in room temperature water for 1 hour and 23 hours in room temperature water.
After extrusion, the sample was immersed in warm water at 80° C. for 8 hours and then in room temperature water for 16 hours for 5 cycles, and after 5 cycles, adhesion was evaluated by a forced peel test. Then, after judging these results using a 5-point scale [5 points (excellent) → 1 point (poor)], the overall score is: ◎...5 points for all, ○...4 points for some, △...2 for some. - 3 points were found, ×... some 1 point was found, and so on. Paint film blistering on end faces - A plastic film coated steel plate with a size of 50 mm x 100 mm with the end faces of the plastic film coated steel plate sealed with polyester tape and the back side sealed with polyester tape was tested in a salt water spray tester (JIS-K-5400, 7). , 8) and evaluated blistering and peeling from the unsealed end surface (hereinafter referred to as edge creep). Evaluation of edge creep was expressed by the maximum bulge width (mm) at the edge, and diagonal cross cuts were made on the film with a knife, and the number and maximum bulge width (mm) at this scratched area were expressed. The results are shown in the table below.

[Table] From the results in the table above, it can be seen that the number and size of blisters on the film surface vary greatly depending on the content of strontium chromate or calcium chromate in the adhesive, and those of Comparative Examples 1 and 2. In the case of Comparative Example 3, the adhesion was good but the swelling was large.
It can be seen that the adhesion is reduced in the case of On the other hand, in the case of Examples, both adhesion and swelling were satisfactory.

[Brief explanation of the drawing]

The attached drawing is a partially cutaway enlarged sectional view of an embodiment of the present invention, in which 1 is an aluminum-zinc alloy plating layer, 2
3 is a chemical conversion treatment layer, 4 is an adhesive, 5 is a plastic film,
6 is an aluminum-rich phase, 7 is a zinc-rich phase, and 8 is a steel plate.

Claims (1)

[Claims] 1. A chemical conversion treatment layer is formed by chemical conversion treatment of the aluminum zinc alloy plating layer on the surface of an aluminum zinc alloy plated steel sheet on which an aluminum zinc alloy plating layer has been formed by hot dipping method, and this chemical conversion treatment layer Strontium chromate or calcium chromate is applied to the surface of
1. A plastic film-coated steel sheet comprising a plastic film coated with an adhesive containing ~50% by weight.