JPH0510154B2 - - Google Patents

Description

[Detailed description of the invention] [Industrial application field]

The present invention has excellent durability by applying and baking an undercoat containing rust-preventive pigments and mica-like iron oxide to a specific plated steel plate, and then applying and baking a topcoat containing acrylonitrile-based fine particles. The present invention relates to a method for producing coated steel sheets.

[Conventional technology]

Conventionally, colored galvanized iron sheets have been the mainstream as exterior building materials for houses, warehouses, etc., but although colored galvanized iron sheets are cheap, they have low durability and are used in industrial areas, coastal areas, suburban areas of cities, mountainous areas, etc. Depending on the location conditions, the useful life is limited to a few years. In recent years, there has been a demand for various highly durable exterior building materials that can be used for a long period of time from the standpoint of resource conservation, and various coated steel sheets are now on the market. For example, painted steel sheets coated with silicone polyester paints or fluororesin paints, which have excellent durability, or paints using aluminum plated steel sheets or Zn-Al alloy plated steel sheets as the base plate instead of galvanized iron sheets. Steel plates are commonly used, and these materials are designed to have improved durability to some extent. However, the improvement in durability of these coated steel plates is only for the flat parts of the coated steel plates, that is, the parts that have not undergone any bending or other processing. The paint film cracks, allowing rainwater to enter through the cracks, causing rust. Therefore, even if a coated steel plate has improved durability on flat areas, its useful life will still be limited to a few years due to the occurrence of rust on processed areas and end faces, and in the end, the actual This does not mean that the durability has improved. In addition, some of the coated metal plates of the present inventors are coated with a paint uniformly containing acrylonitrile-based polymer fine particles and mica-like iron oxide particles as coated metal plates that are also used as exterior building materials. It was invented and disclosed earlier by others (Japanese Unexamined Patent Publication No. 1983
-Refer to No. 3867). However, although this painted metal plate is designed primarily for the matte effect and has excellent physical properties of the coating film, it is not necessarily satisfactory in terms of the rust prevention effect on processed parts and end faces. It wasn't a kimono. Under such circumstances,
There has been a demand for a coated steel plate with excellent durability that does not rust on flat parts, processed parts, or end faces when actually used as an exterior building material.

[Problems to be solved by the invention]

The inventors of the present invention conducted extensive studies to meet the above-mentioned demands, and as a result, found the following. In other words, painted aluminum-plated steel sheets and Zn-Al alloy-plated steel sheets have less white rust, red rust, and paint blistering in salt water environments than colored galvanized steel sheets, and have good corrosion resistance, but they do not tolerate corrosion in humid environments. The reason why the corrosion resistance is particularly poor in areas where the iron base of the painted original plate is exposed, such as processed areas, end faces, and other parts where the paint film is damaged (hereinafter sometimes referred to as processed areas), is due to the fact that it is in a humid environment. It was determined that this was because an oxide film of aluminum formed on the surface of the original plate exposed to the outside air, and the sacrificial corrosion protection effect of aluminum on iron parts was no longer maintained. In addition, in the above-mentioned invention, it was determined that the reason why the occurrence of rust in processed parts etc. cannot be satisfactorily prevented is because mica-like iron oxide is also present on the surface of the paint film, so the paint film is coated with an undercoat. Although the method was divided into two layers, a film layer and a topcoat layer, and the mica-like iron oxide was present only in the undercoat layer, a fully satisfactory result could not be obtained. Even after obtaining the above knowledge, we continued to study with the aim of providing a method for manufacturing coated steel sheets with excellent durability that prevents rust from forming in processed parts, etc. As a result, we decided to use aluminum plating as a base plate for painting. steel plate or
A plated steel plate containing at least aluminum as a plating component, such as a Zn-Al alloy plated steel plate, is used, and the mica-like iron oxide and anti-corrosion pigment are present only in the undercoat layer of the coating layer, and the top coat layer is used. The present invention was completed after discovering that it was possible to produce a coated steel sheet that could satisfactorily prevent the occurrence of rust in processed areas, etc. by including fine particles of acrylonitrile polymer in the layer. did.

[Means to solve the problem]

That is, in the present invention, after chemically treating a plated steel sheet containing at least aluminum as a plating component, 5 parts by weight of a rust preventive pigment is added to 100 parts by weight of the resin forming the coating film.
An undercoat containing ~30 parts by weight and 5 to 50 parts by weight of mica-like iron oxide particles is applied and baked, and then polyacrylonitrile polymer is added to 100 parts by weight of non-volatile matter other than fine particles of polyacrylonitrile polymer. The present invention relates to a method for producing a coated steel sheet with excellent durability, which comprises applying and baking a top coat containing 5 to 50 parts by weight of fine particles. The present invention will be explained in detail below with reference to the drawings. The figure is a cross-sectional view schematically showing an example of a coated steel plate obtained by the present invention. Examples of the plated steel plate containing at least aluminum as a plating component used as a coating base plate in the present invention include aluminum plated steel plate, Zn-Al
Examples include alloy-plated steel sheets, Al-Si alloy-plated steel sheets, and the like. These are usually obtained by applying hot-dip plating to the above-mentioned plated steel sheets, but aluminum-plated steel sheets, for example, can also be obtained by electroplating or vapor deposition plating. Prior to painting such a plated steel plate, a chemical conversion treatment is applied according to a commonly used method. After the above-mentioned plated steel plate is subjected to chemical conversion treatment, an undercoat paint, which will be described below, is applied and baked thereon.
The undercoat contains 5 to 30 parts by weight of a rust preventive pigment and 5 to 50 parts by weight of mica-like iron oxide particles per 100 parts by weight of the coating resin. Anti-rust pigments include zinc chromate, strontium chromate,
Chromates such as calcium chromate have the best effect, but phosphates, polyphosphates, molybdates, etc. can also have good effects. These antirust pigments can be used alone or in combination of two or more. Mica-like iron oxide particles (hereinafter sometimes abbreviated as MIO) have a scale-like shape, and are highly effective against corrosion-promoting factors such as rainwater and ultraviolet rays that penetrate through the top coat, which will be explained later. It has a shielding effect. If the content of MIO exceeds 50 parts by weight based on 100 parts by weight of the resin constituting the coating film, the surface appearance of the coating film will be impaired and the dispersibility in the coating material will be lacking, resulting in a decrease in coating workability. Workability is also poor. When the content of MIO is less than 5 parts by weight, the above-mentioned shielding effect is insufficient. Regarding the size of MIO, there is no need to limit it in particular as it can be used over a wide range of sizes in the present invention, where it is present only in the undercoat film together with the anti-corrosion pigment, but if it is too large, it will damage the surface of the paint film. 10 μm or more is very preferable because there is a risk of forming unevenness on the surface and impairing the aesthetic appearance, and if it is too small, the above-mentioned shielding effect will deteriorate.
The thickness is about 50μ, and the most preferable range is 10μ to 20μ. The coating film-constituting resin is, for example, acrylic acid ester in acrylic paints, oil-modified alkyd in alkyd paints, epoxy resin in epoxy paints, novolak in phenolic paints, etc., which are used after coating and baking. Refers to the things that make up the membrane. 5 to 30 parts of rust-preventing pigment per 100 parts by weight of such coating film-constituting resin.
An undercoat containing 5 to 50 parts by weight of MIO and 5 to 50 parts by weight of MIO may be prepared from scratch using the respective raw materials for the paint, or an anticorrosive pigment and/or MIO and/or may be added to an available ready-made paint. Or, even if the amount of the coating film-constituting resin is adjusted to a predetermined weight part ratio,
Further, if necessary, it may be adjusted by adding and mixing with a solvent or the like. In this case, for ready-made paints whose component weight ratios are unknown, if they do not contain rust-preventing pigments and MIO, it can be assumed that the nonvolatile content corresponds to the amount of the resin forming the paint film. A commonly used method may be used to apply and bake the undercoat paint prepared in this way onto the chemical conversion-treated plated steel plate. After the undercoat paint is applied and baked, a topcoat paint, which will be described below, is then applied and baked thereon.
The top coating is a paint containing 5 to 50 parts by weight of polyacrylonitrile polymer particles per 100 parts by weight of non-volatile components other than the polyacrylonitrile polymer. Pigments are used for hiding and coloring the base, and are distinguished from the anti-rust pigments. The polyacrylonitrile polymer (hereinafter sometimes abbreviated as PAN) fine particles used in the top coat are spherical PAN fine particles that have virtually no internal voids, preferably PAN with an acrylonitrile content of 80% by weight or more. Consisting of
The average particle size is preferably in the range of 2 to 200 microns. To obtain such PAN microparticles,
For example, the method disclosed in Japanese Patent Application Laid-Open No. 52-8090,
That is, by polymerizing in water a monomer mixture consisting of an ethylenically unsaturated compound containing acrylonitrile as a main component and the remainder containing gasulfonic acid or its salt, a sulfonic acid group or its salt is introduced into the resulting polymer. With this, an aqueous dispersion of polymer droplets in which the polymer particles are substantially in a molten state is formed, and then the polymer droplets are cooled with stirring to prevent coalescence, resulting in a substantially spherical solidified dispersion. Spray drying and granulating an aqueous dispersion containing PAN fine particles to produce PAN with a desired particle size range.
It can be made into fine particles. Such PAN fine particles are hard and can be uniformly dispersed in a large amount in the top coat. Therefore, the top coat formed by coating and baking has PAN fine particles uniformly dispersed therein. Since these PAN fine particles have excellent adhesion to the coating resin and are themselves very weather resistant, the top coat is a coating with excellent weather resistance and abrasion resistance. It becomes a membrane.
If the content of PAN fine particles exceeds 50 parts by weight per 100 parts by weight of non-volatile matter (mainly the total amount of coating film constituent resin and pigment), although it has the effect of further improving weather resistance, it may not be uniformly distributed in the paint. Furthermore, the increased viscosity of the paint reduces coating workability, and the formed coating film becomes non-uniform and hard, resulting in a marked decrease in workability of the resulting coated steel sheet. Furthermore, if the content of PAN fine particles is less than 5 parts by weight, the weather resistance of the coating film will be insufficient, and the object of the present invention will not be achieved. The content of PAN fine particles is determined based on the nonvolatile content (mainly the total amount of coating film constituent resin and pigment).
This is because the weather resistance of a coating film is determined not only by the deterioration of the resin that constitutes the coating film, which is the matrix of the coating film, but also by the discoloration of the pigments in the coating film. To prepare the top coat, you can prepare it from the beginning using each raw material of the paint, or you can prepare it from the available ready-made paint.
The amount of the PAN fine particles and/or the pigment and/or the resin constituting the coating film may be adjusted to a predetermined weight part ratio, or if necessary, the composition may be prepared by adding and mixing with a solvent or the like. A commonly used method may be used to apply and bake the top coat on the base coat.

[Action and effect]

As schematically shown in the figure, the coated steel sheet manufactured as described above according to the present invention has the surface of the plated steel sheet 1 containing at least aluminum as a plating component coated with a chemical conversion film 2, and An undercoat film layer 3 containing a mixture of a rust preventive pigment 4 and mica-like iron oxide particles (MIO) 5 is formed on the base coat.
Further, by having a cross-sectional structure in which a top coat layer 6 uniformly containing PAN fine particles 7 is formed thereon, it has various advantages as follows. That is, since MIO5 is contained only in the undercoat film layer 3, there is extremely little risk of damaging the topcoat film during processing. Since a large amount of PAN fine particles 7 are uniformly present in the top coat layer 6, the weather resistance of the top coat layer 6 is extremely excellent even when directly influenced by the external environment.
Even if the topcoat film layer 6 is damaged, it has a strong effect of preventing the progress of deterioration of the paint film due to the external environment, so it is difficult to affect the deep parts. Even if corrosion-promoting factors such as water and ions reach the undercoat layer 3 through the topcoat layer 6 for some reason, the anticorrosion pigment 4 and MIO 5 are allowed to coexist in the undercoat layer 3. Due to the chemical action of anti-rust pigment 4 and MIO5
A very strong anti-corrosion effect is achieved by the mutually complementary physical shielding effect. Since the surface of the plated steel plate 1 is not exposed to the outside air, an oxide film does not form on the aluminum plated metal even in a humid environment, and the sacrificial corrosion protection effect on the iron parts can be maintained. Therefore, the coated steel sheet manufactured by the present invention has various advantages as mentioned above, and even if it is processed and used as an exterior building material, it will hardly be corroded by water, ions, etc. that enter from the processed parts etc. It is a coated steel plate with excellent durability that can completely prevent damage. EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to the Examples. It should be noted that all numerical values indicating compounding ratios described in Examples and Comparative Examples are in parts by weight unless otherwise specified.

【Example】

Examples 1 to 16, Comparative Examples 1 to 21 20 parts by weight of zinc chromate and an average particle size of 15 μ per 100 parts by weight of the above resin were added to a thermosetting epoxy solvent-based paint with a resin content of 40% by weight. An undercoat paint was prepared by adding and mixing MIO of 100% by weight with various parts by weight ranging from 0 to 55 parts by weight as shown in the table.
In addition, a brown thermosetting polyester paint containing red iron and carbon black pigments and a thermosetting acrylic resin paint of the same color containing the same pigments were used separately, and each was mixed with 100 parts by weight of non-volatile content. PAN fine particles with an average particle size of 15μ (manufactured by Nippon Exlan Kogyo KK, trade name: Toughchik) were mixed in various weight parts ranging from 0 to 55 parts by weight as shown in the table (0 parts by weight is only when polyester paint is used). Two types of top coats were prepared by adding and mixing to uniformly disperse. Aluminum-plated steel sheets, Zn-55% Al (Zn45% by weight, Al55% by weight) alloy-plated steel sheets, and Zn-4%Al (Zn96% by weight, Al4
(weight%) alloy-plated steel plates were used, and the sizes of both were 200 mm x 300 mm x 0.35 mm (plate thickness). Before painting these plated steel plates, apply a phosphoric acid chromate treatment solution (manufactured by Nippon Paint KK, trade name: Allozin 407-47,
A chromium coating amount of 25 mg/m ² ) was used, and a phosphate-based treatment solution (manufactured by Nihon Parkerizing KK, trade name Bonderite 1310, chromium coating amount of 10 mg/m ² ) was used for Zn-Al alloy plated steel sheets. Chemically treated. The above-mentioned undercoat paint was applied to a chemical conversion treated steel plate so that the film thickness after drying would be 7μ, baked and dried for 30 seconds at a final board temperature of 200±10℃, and then the above two types of topcoat paints were applied. One of these was applied so that the coating thickness after drying was 20 μm, and baked and dried in the same manner as in the case of the undercoat to obtain a coated steel plate. The combinations of top coat and undercoat paint are as shown in the table, and in each comparative example except Comparative Example 21 in which only one type of paint was used, either one or both of the top coat and undercoat paint is used in the present invention. It is of a composition outside the scope of the invention. In Comparative Example 21, 20 parts by weight of MIO was added to 100 parts by weight of the non-volatile content of the thermosetting polyester paint.
Add 10 parts by weight of PAN fine particles and mix with MIO.
A top coat containing PAN in the same paint was prepared, and an undercoat was prepared by adding only 20 parts by weight of zinc chromate to 100 parts by weight of the resin for forming the coating film of the thermosetting epoxy solvent-based paint. Prepare
This is a case in which the undercoat paint and the topcoat paint were applied and baked in the same manner so that the film thicknesses were the same as in the above example. Each coated steel sheet thus obtained was processed under certain conditions as described below, and was then subjected to a corrosion resistance test (salt spray test and zinc acid gas test) and a weather resistance test to evaluate its performance. The painted steel plate is processed by bending it approximately 180 degrees in about 1 second around a rod with a diameter of approximately 2 mm with the painted surface facing outward.
Place 3 plates of the same thickness as the painted steel plate on the inside of the bent part.
I used a method of sandwiching the pieces and rapidly tightening them in a vise. The coated steel sheets processed in this way were used as test pieces and various tests were conducted in accordance with the following. The state of the coating film and the state of rust occurrence were observed and evaluated. (i) Corrosion resistance test Salt spray test Compliant with JIS Z 2371. Test time: 3000 hours Sulfur dioxide gas test The test was conducted using a sulfur dioxide gas test device based on JIS D 0201. Test time: 500 hours, SO ₂ concentration: 100ppm, Temperature: 40℃, Humidity (RH): 90% or more After the test, the flat part, end face, and processed part of each specimen were observed using a 10x magnifying glass. and evaluated based on the following criteria. ◎: No blisters on the paint film ○: Slight blisters on the paint film △: Blisters on the paint film ×: Blisters and rust on the paint film (ii) Weather resistance test JIS K 2246 (using Sunshine Weather Meter) for 2000 hours, and the color difference (ΔE) of each test piece after the test was measured using Color Analyzer Model 307 manufactured by Hitachi, Ltd. The above is summarized in the table below.

【table】

【table】

[Table] As can be seen from the table, when an aluminum plated steel plate is used as the original plate for coating, the corrosion resistance of the coated steel plates of Examples 1 to 8 obtained by the present invention is not limited to the salt spray test as well as the severe test. Even in the so-called sulfur dioxide gas test, there was no blistering or rust on the paint film, not only on flat areas, but also on edge areas and processed areas.
It shows extremely excellent performance. On the contrary, MIO and
In Comparative Examples 1 to 9, in which PAN fine particles were contained, but the content was outside the range of those used in the present invention, at least slight blistering of the coating film was observed in the end face and processed parts in the salt spray test. In the sulfur dioxide gas test, the same phenomenon was observed in most of the flat areas. In addition, when a Zn-Al alloy plated steel plate is used as the original plate for painting, there is a tendency for the overall performance to be slightly inferior to that when an aluminum plated steel plate is used, but still, Examples 9 to 9
As can be seen from Comparative Examples 10 and 11, the painted steel sheet according to the present invention has sufficiently excellent performance.
The performance is inferior. On the other hand, as for weather resistance, as can be seen from Examples 1 to 16, the coated steel sheets obtained by the present invention all have △E in the range of 0.5 to 0.8 and exhibit excellent performance. In Comparative Examples 3, 5, and 9, in which a small amount of was used, ΔE was 2.0, indicating that the weather resistance was poor. Comparative Examples 12 to 20 either contain no MIO in the undercoat or contain MIO in the topcoat.
It contains either no PAN fine particles or both, and as can be seen from the table, painted steel sheets using such paints have extremely poor corrosion resistance, weather resistance, or both.
Furthermore, when MIO and PAN fine particles are mixed in the coating film, as seen in Comparative Example 21, the corrosion resistance is insufficient. As described in detail above, according to the present invention, an anti-rust pigment and MIO are contained in an undercoat, and PAN fine particles are contained in a topcoat to coat a plated steel sheet containing at least aluminum as a plating component. By coating and baking to form a two-layer coating, a coated steel sheet with excellent corrosion resistance and weather resistance can be obtained.

[Brief explanation of the drawing]

The figure is a cross-sectional view schematically showing an example of a coated steel plate obtained by the present invention. DESCRIPTION OF SYMBOLS 1... Plated steel plate, 2... Chemical conversion film, 3... Undercoat film layer, 4... Antirust pigment, 5... Mica-like iron oxide (MIO), 6... Top coat film layer, 7... PAN
Fine particles.

Claims (1)

[Claims] 1. After chemical conversion treatment of a plated steel sheet containing at least aluminum as a plating component, coating film-constituting resin is applied.
An undercoat containing 5 to 30 parts by weight of a rust preventive pigment and 5 to 50 parts by weight of mica-like iron oxide particles per 100 parts by weight is applied and baked, and then 100 parts by weight of non-volatile matter other than polyacrylonitrile polymer particles are applied. 5 parts by weight of polyacrylonitrile polymer fine particles
A method for producing a coated steel sheet with excellent durability, characterized by applying and baking a top coat containing ~50 parts by weight. 2. The method for producing a coated steel sheet with excellent durability according to claim 1, wherein the plated steel sheet containing at least aluminum as a plating component is an aluminum-plated steel sheet. 3. The method for producing a coated steel sheet with excellent durability according to claim 1, wherein the plated steel sheet containing at least aluminum as a plating component is a Zn-Al alloy plated steel sheet. 4. The method for producing a coated steel sheet with excellent durability according to claim 1, wherein the plated steel sheet containing at least aluminum as a plating component is an Al-Si alloy plated steel sheet. 5. The method for producing a coated steel sheet with excellent durability according to any one of claims 1 to 4, which uses chromate as a rust-preventive pigment. 6 Forms scale-like mica-like iron oxide particles and 10
The method for producing a coated steel plate with excellent durability according to any one of claims 1 to 5, wherein a steel plate having a size of 50 μm is used. 7 Polyacrylonitrile polymer fine particles that are spherical with virtually no internal voids, have an acrylonitrile content of 80% by weight or more, and have an average particle size of 2 to 200μ
Claims 1 to 6 that use
A method for producing a coated steel plate with excellent durability according to any one of the preceding items.