JPH0576830A - Production of painted metal plate excellent in film adhesion - Google Patents

Abstract

PURPOSE:To certainly improve the bonding durability between a chemical forming film and a paint film, especially, the water-resistant adhesion therebetween by applying baking curable resin paint containing a crosslinking agent to a metal pallet subjected to substrate treatment to bake the paint layer to form a first paint film and applying paint to said film to bake the same so as to obtain an objective film thickness. CONSTITUTION:Baking curable resin paint containing a crosilinking agent diluted so that the concn. of a resin solid becomes 1-10000ppm is applied to a metal plate which is subjected to phosphate type and/or chromate type substrate treatment and baked to form a first paint film layer and paint is applied to the paint film to be baked so as to obtain an objective film thickness. That is, the first paint film is provided in extremely thin film thickness not generating thickening in order to prevent crosslinking reaction from becoming by the formation of a thickening layer in the vicinity of the interface on the matrix side of the paint film layer and this thin film is baked and cured in order to prevent thickening thereafter. By this method, an uncured part where crosslinking reaction is imperfect can be eliminated or minimized.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for producing a coated metal plate such as a coated steel plate. The coated metal sheet produced by the present invention has excellent coating film adhesion, and is expected to be applied as a coated steel sheet for bonded structures. Specifically, it can be used for applications such as fluorescent lamps, home electric appliances such as refrigerators, steel furniture, building materials, etc., and in the future, it can be considered to be applied to automobiles and the like. In the following, a coated steel sheet, which is a typical coated metal sheet, will be mainly described, but the present invention is not limited to the coated steel sheet.

[0002]

2. Description of the Related Art Painted steel sheets, which have been pre-painted on steel sheets, are advantageous in terms of resource saving, pollution prevention, etc., because complicated coating processes for customers can be omitted. Demand is increasing year by year mainly for home electric appliances, etc., due to its excellent image quality. Generally, coated steel sheets are
On steel plate base material such as cold rolled steel plate or zinc-based plated steel plate,
It is manufactured by applying a chemical conversion treatment such as chromate or zinc phosphate and then coating. However, in the coated steel sheet, the chemical conversion film and the coating film do not have electrical conductivity, and spot welding cannot be used, so that the application site thereof is remarkably limited.

If mechanical joining by "caulking" is adopted as a joining method instead of welding, the coating film is destroyed and the appearance and corrosion resistance of the product are significantly lowered. Therefore, with the development of a strong adhesive in recent years, the joining of coated steel sheets has come to be performed by the adhesive. Painted steel sheets suitable for bonding are
For example, it is proposed in JP-A-62-225341 and JP-A-1-85753.

However, it has often been experienced that it is difficult to secure long-term reliability (durability) when conventional coated steel sheets are joined with an adhesive. In particular,
When the paint constituting the coating film is a cross-linking type multi-component coating material containing various resin components, the adhesion durability at the chemical conversion film and the coating film interface on the steel sheet base metal, that is, the coating film adhesion, especially The water-resistant adhesion was sometimes insufficient. For example, in a polyester / melamine cross-linking type primer coating film, if the types and relative proportions of the polyester type and melamine type are changed, the adhesive durability at the chemical conversion film / coating film interface of the coated steel sheet is significantly changed, Water resistance of the coating film is often insufficient.

Therefore, in the production of a coated steel sheet for adhesive bonding, in addition to the good general coating film physical properties that have been considered in the past, the initial adhesiveness and durable adhesiveness of the adhesive structure are secured. Must. However, it is difficult to satisfy all of these performances, and it has been at best to select the coating composition so that these performances are appropriately balanced.

Forcibly peeling after the adhesive joint of a coated steel sheet has been exposed for a long period of time often results in peeling at the coating / priming interface. That is, the interface that causes the most problems in durability is not the adhesive / coating film interface but the interface on the base material side of the coating film. In order to improve the durability of this portion and enhance the adhesion durability of the coated steel sheet, the present inventors have previously developed an ultra-thin film layer of polyester or epoxy resin on a base treatment layer formed by zinc phosphate or chromate treatment. Was proposed in advance (Japanese Patent Application No. 3-45062). This method is effective for improving the adhesion durability of the coated steel sheet, but in some cases, the adhesion durability may not be sufficiently improved even if such treatment is performed.

[0007]

The object of the present invention is to provide a coating metal capable of reliably improving the coating film adhesion of coated steel sheets, that is, the adhesion durability between the chemical conversion film / coating film, especially the water resistance adhesion. Is to provide a plate.

[0008]

Means for Solving the Problems The inventors of the present invention have investigated the cause of insufficient improvement of the adhesion durability by the above-mentioned treatment for forming an ultra-thin film layer in advance, and as a result, have found that a coating on the thin film layer When painting, depending on the type of thinner in the paint,
It has been found that the thin film layer formed with a certain amount of time may dissolve in this thinner, and this dissolution causes a decrease in adhesion durability.

In order to prevent this, before applying the desired coating, a bake-curable coating material containing a crosslinking agent is highly diluted to a coating of an extremely thin film thickness of 1 μm or less, and then this thin film is formed. The inventors have found that the above object can be achieved by baking and curing the above, and have completed the present invention. That is, in the method of the present invention, since the thin film layer formed in advance is cross-linked before coating of the target coating material, there is no fear of dissolution due to thinner in the coating material applied thereon, and the film is firmly fixed by the base treatment. Therefore, good durability is surely exhibited.

Here, the gist of the present invention is that a cross-linking agent is prepared by diluting a metal plate having a phosphate and / or chromate base treatment to a resin solid concentration of 1 to 10,000 ppm. A coated metal plate, comprising: baking and curing a bake-curable resin coating containing the above to form a first coating film layer, and then coating and baking the coating film on the coating film so that a target coating film thickness is obtained. Manufacturing method.

The base material of the coated metal sheet of the present invention may be any metal sheet, such as hot-dip zinc or zinc alloy plated steel sheet, galvanized zinc or zinc alloy plated steel sheet, alloyed hot dip galvanized steel sheet, and further stainless steel. It includes various steel plates including steel plates and cold rolled steel plates, and non-ferrous metal plates such as aluminum plates and titanium plates. Hereinafter, in order to simplify the description, similarly to the above, the present invention will be described mainly with respect to a coated steel plate whose base material is a steel plate, but those skilled in the art will understand that the same applies when the base material is a non-ferrous metal plate. Be understood.

[0012]

In the coating film of a coated steel sheet, a specific resin component is concentrated on the surface of the coating film after coating, especially during baking. As a result of detailed investigation of this phenomenon, the present inventors concentrated another similar resin component in the vicinity of the base material side interface of the coating film (the interface in contact with the chemical conversion film). It was found that in the membrane, the cross-linking reaction in the vicinity of this interface is not sufficiently performed, and the reinforcing effect due to the cross-link cannot be expected sufficiently.

In the present invention, in order to prevent the crosslinking reaction from being incomplete due to the formation of such a thickened layer near the interface on the base material side of the coating film, an ultrathin film in which thickening cannot occur. A thick first coating layer is provided, and this thin film is baked and cured to prevent subsequent thickening. This method eliminates or minimizes uncured areas with incomplete crosslinking reactions. In this way, it is important to preliminarily provide a resin layer that has been uniformly and strongly crosslinked / cured on the undercoating layer, and it is important not to create a portion with weak cohesive strength at the interface with the base metal. It is important for improving the coating film adhesion of coated steel sheets with paint.

The type of paint used for producing the coated steel sheet of the present invention is not particularly limited. Many ordinary bake-curable paints are multi-component paints that have a composition in which another resin that functions as a crosslinking agent is mixed with a base resin. Examples of useful paints include
Examples thereof include polyester coatings containing a melamine resin and isocyanate as a cross-linking agent, amino alkyd resin coatings containing an amino resin and an alkyd resin, and epoxy coatings containing an amino resin and a phenol resin as a cross-linking agent.

In the method for producing a coated steel sheet according to the present invention,
First, the base steel sheet is subjected to a phosphate-based and / or chromate-based undercoating treatment to form an underlying chemical conversion coating on the base steel sheet. This base treatment is essential to secure the adhesion of the coating film. These base treatments are conventional treatments and may be performed in the same manner as in the past.

Next, the resin solid content concentration is 1 to 10,000 ppm.
A bake-curable resin paint containing a cross-linking agent, which is diluted with a suitable solvent so that the above, is applied and baked to form the first coating layer. The reason for highly diluting in this way is to generate an extremely thin first coating film layer having a thickness equal to or smaller than the film thickness of the concentrated layer which is generated when the originally intended coating layer (main coating layer) is provided. The thickness of the thickened layer formed varies depending on the resin system, but is on the order of several tens to several thousands Å, that is, an ultrathin film of less than 1 μm. If the resin solids concentration exceeds 10,000 ppm, the thickness of the first coating layer that forms will exceed this range, and a concentrated layer will be formed near the interfaces on both sides of the coating, where specific resin components are concentrated. Therefore, the object of the present invention cannot be achieved.

The driving force for thickening a specific component in a multi-component coating film is considered to be the difference in surface tension between the components. That is,
Resins with high polarity concentrate near the interface with the base material, and those with low polarity concentrate near the surface (interface with air). It is not known whether such thickening occurs in the ultra-thin first coating layer of less than 1 μm as formed by the present invention, but the surface tension that is usually considered for such ultra-thin films is unknown.
It is a thin film region of a molecular order different from (a clear distinction is recognized between the surface and the bulk), and a clear distinction between the surface and the bulk is difficult. Therefore, in this ultra-thin first coating layer, the cross-linking reaction occurs almost uniformly, and there are no sites where the cross-linking reaction is incomplete, so the adhesion durability between the coating film and the base material is secured, and the coating film It is presumed that the adhesion and the water resistance adhesion are improved.

The paint used for forming the first coating layer may be any paint as long as it is a bake-curable resin paint containing a crosslinking agent. That is, it may be the same or the same paint system as the paint used for forming the present paint layer coated thereon, or a different paint system. Further, the solvent for dilution may be appropriately selected according to the resin type in the coating material used.

The method of applying the diluted coating material to form the first coating layer is not particularly limited. Although roll coating similar to normal primer coating can be adopted, since the solid content concentration of the paint is very low, it is possible to adopt a simple coating method that does not use rolls, such as dip coating, spraying, curtain flow coating. it can. Thereby, the coating process of the first coating layer can be carried out very simply and easily.

After the above-mentioned diluted paint is applied, this coating film is baked and cured to crosslink and cure the first coating film layer. The baking conditions are selected according to the paint system used. If the first coating layer is not cross-linked and cured, the resin component in the first coating layer will be dissolved by the solvent contained in the coating when the coating is applied to form the coating layer on it. However, a concentrated layer is newly formed near the interface with the base material. That is, by crosslinking and curing the first coating layer, the resin is fixed so that the resin does not move near the interface with the base material.

Thereafter, a bake-curable resin coating material which is the same as or different from the first coating layer is used for coating by a conventional method, followed by bake-curing to form the main coating layer. The bake-curable paint used to form this paint layer is 1
It may be a component system, and this paint may be a so-called primer. The thickness of the paint layer is usually in the range of several μm to several tens of μm. Thereafter, if desired, one or more coating layers may be further formed for the purpose of intermediate coating, top coating, and the like. The paint system used for this is not limited at all.

If necessary, in order to improve the surface adhesiveness of the coated steel sheet, surface modification treatment may be carried out by various conventionally proposed methods. Also, if the adhesion between the ultra-thin first coating layer and this coating layer (for example, a normal primer coating layer) is poor, after forming the first coating layer by coating baking, This layer may be subjected to a modification treatment for improvement.

Since the coated steel sheet produced by the method of the present invention has excellent coating film adhesion, it is suitable for producing various home electric appliances, building materials, office equipment, steel furniture, etc. using an adhesive. is there. Since the coating film is firmly bonded to the base material through uniform cross-linking, there is no risk of peeling at the base material (chemical conversion film) / coating film interface, unlike conventional coated steel sheets, even after long-term use. Due to its high water-resistant adhesion, it is also useful for products that are used outdoors and for products that are exposed to water such as washing machines.

Next, the present invention will be specifically described with reference to examples, but the present invention is not limited to the examples. In the examples, all parts are parts by weight.

[0025]

Example 1 Hot-dip galvanized steel sheet (one side areal weight 60 g /
One surface of m ² ) was treated with zinc phosphate (adhesion amount: 1 g / m ² ) and chromate rinse (adhesion amount: 5 mg / m ² as Cr) in order by a conventional method to perform a chemical conversion treatment on the underlayer. A two-layer coating film was formed by the method of the present invention on the conversion coating layer obtained by this base treatment, using a polyester-based coating containing a melamine resin as a crosslinking agent. The paint used was prepared by mixing 100 parts of a polyester resin paint (Vylon 29CS manufactured by Toyobo) with 10 parts of a melamine resin paint (Super Beckamine J820 manufactured by Dainippon Ink) as a crosslinking agent.

The first coating layer was prepared by diluting this coating material with cyclohexanone to a resin solids concentration of 10 ppm and applying it with a bar coater # 10. It was formed by baking and curing for 2 seconds. Then, bar-coat the same undiluted paint to a dry film thickness of 10 μm, and bake cure under the same conditions as above,
This paint layer was formed to obtain a coated steel sheet.

[0027]

[Comparative Example 1] The method of Example 1 was repeated except that the first coating layer was not formed, and the paint was directly applied on the base-treated steel sheet so as to have a dry film thickness of 10 µm and baked. Cured. That is, the coating layer is one layer made of crosslinked polyester.

[0028]

[Example 2] Epoxy resin (Epicote 82 made by Yuka Shell
8) Using the paint prepared by mixing 20 parts of the melamine resin paint used in Example 1 as a cross-linking agent in 100 parts, in the same manner as in Example 1, the method of the present invention was applied to a hot-dip galvanized steel sheet that had been pretreated. To form a two-layer coating film. That is, both the first coating layer of the thin film and this coating layer are
It was formed by a melamine paint. The dry film thickness of this paint layer was 5 μm.

[0029]

Comparative Example 2 The method of Example 2 was repeated, except that the epoxy-melamine-based paint was directly applied to the base-treated steel sheet to form a dry film thickness of 5 μm without forming the first coating layer. Painted and baked and cured.

[0030]

Example 3 The first coating layer of a thin film was formed on the hot-dip galvanized steel sheet subjected to the surface treatment in the same manner as in Example 1 by using the polyester-melamine-based coating material described in Example 1. The degree of dilution of the paint, the diluent solvent, the coating method, the baking conditions, etc. were all the same as in Example 1. The epoxy-melamine-based coating material described in Example 2 was used to form a cured coating film having a dry film thickness of 5 μm on the crosslinked and cured first coating film layer in the same manner as in Example 2 to form the upper layer and the lower layer. Painted steel sheets having different paint types were prepared by the method of the present invention.

The initial and secondary bond strengths of the coated steel sheets obtained in the above Examples and Comparative Examples were measured. The adhesive strength was measured as peel strength by T-type peeling after preparing two test pieces of each coated steel sheet and laminating the coated surfaces with a two-component urethane adhesive. Secondary adhesive strength is 80 ℃
* Adhesive strength measured after immersion in hot water for 14 days. The test results are summarized in Table 1 below.

[0032]

[Table 1]

Initially, all coated steel sheets showed cohesive failure of the adhesive and had good coating adhesion, but after immersion in hot water at 80 ° C. for 14 days, all coatings in the comparative example were coated. The interface is peeled off, and the difference from each example in which cohesive failure of the adhesive is recognized is large. This is because in the example, a crosslinked resin layer is formed near the interface, and the coating film continues to be firmly bonded to the base material,
It is thought that this is because of its excellent water resistance.

[0034]

As described above, according to the method of the present invention, an extremely thin cross-linked cured coating film is formed using a highly diluted resin composition containing a cross-linking agent before the main coating, whereby adhesion of the coating film is improved. It is possible to remarkably improve the adhesiveness, especially the water-resistant adhesiveness after aging, and prevent the deterioration of the adhesion durability, which is observed in the products assembled with conventional coated steel sheets with an adhesive, and the durability of the products. The practical effect on is remarkable. Also,
By using the method of the present invention, the degree of freedom in paint design can be expanded, and a paint metal plate having excellent coating film adhesion can be easily produced using a paint system having various excellent performances. Like

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Office reference number FI technical display location C23C 22/33 8520-4K // B32B 15/08 G 7148-4F

Claims (1)

[Claims] 1. A resin plate having a solid concentration of 1 to 1 on a metal plate which has been subjected to a phosphate-based and / or chromate-based undertreatment.
Baking-curable resin paint containing a crosslinking agent diluted to 10,000 ppm is applied to form a first paint film layer, and then paint is applied to the paint film to achieve the desired paint film thickness. A method for producing a coated metal plate, which comprises baking.