JP2973868B2 - Hot-dip galvanized steel sheet with excellent adhesive bonding properties - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a hot-dip galvanized steel sheet used for automobiles, building materials, containers and the like.

[0002]

2. Description of the Related Art Galvanized steel sheets, alloyed galvanized steel sheets, or alloy-coated steel sheets of zinc and other metals (hereinafter, referred to as "metallic steel sheets").
In addition, zinc-coated steel sheets) have been widely used in automobiles, home appliances, outdoor equipment, building materials, and the like because of their excellent corrosion resistance. In particular, when used as a material for automobiles, various zinc-based alloy-plated steel sheets have been developed due to the requirement of corrosion resistance in the usage environment.

[0003] In the case of automobiles, these plated steel sheets are incorporated into products through various processes such as processing, forming and joining when used, and spot welding is frequently used as a joining method. However, since spot welding is not always sufficient as a joining method, application of adhesive joining using an adhesive has been studied. Adhesive bonding is considered to be advantageous in that it can reduce the weight of the product, improve rigidity, and can join different materials, compared to spot welding. With respect to such a usage, one of the properties that a steel sheet should have is that it has excellent adhesive bonding properties in addition to the conventional corrosion resistance, paintability, and spot weldability.

[0004] As is well known, when a metal is bonded with a resin-based adhesive, the adhesive force is a mechanical anchoring effect between the metal surface and the adhesive and a chemical attractive force due to hydrogen bonding or the like. It is said that the union will be decided. The surface of many metals is covered with an extremely thin film of a nonmetallic compound such as an oxide formed by reacting with oxygen in the atmosphere, and the properties of the film also affect the adhesiveness.

[0005] Zinc-coated steel sheets are industrially manufactured by a hot-dip plating method or an electroplating method.
Adhesive bondability is inferior to a cold-rolled steel sheet that is not plated. In particular, the galvanized steel sheet manufactured by the hot-dip plating method has poor adhesion as compared with the case of the electroplating method. In the hot-dip galvanized steel sheet, there are few irregularities on the surface that enhance the mechanical anchoring effect, and oils and fats that deteriorate the wettability of the adhesive adhere to the surface. It can be considered that oxides, phosphates, phosphates, silicates, heavy metal oxyacids, etc. adhere in large amounts due to contamination during handling and the amount thereof is not constant, and thus it is considered that the adhesive bonding property is not good. For this reason, fats and oils on the surface are removed with a degreasing solvent or the like, and products and deposits on the surface are removed by mechanical polishing. However, it is troublesome and the improvement in adhesiveness is not always sufficient.

[0006] The thickness of the plating layer of the hot-dip galvanized steel sheet is about several μm, but the thickness of the extreme surface layer involved in the adhesive bonding made of the above-mentioned nonmetallic compound is several nm. Focusing on this extreme surface layer, as an invention to improve the adhesive bonding property of hot-dip galvanized steel sheet, JP-A-6-10156 discloses that
After the surface is cleaned, an oxide film is formed on the outermost surface layer to a thickness of 1 nm or more, and the molar ratio of aluminum oxide (Al ₂ O ₃ ) to zinc oxide (Zn 0) in the oxide film layer is 0.5 or less. Steel sheet is presented. However, in the case of a hot-dip galvanized steel sheet that is generally manufactured, the molar ratio of aluminum oxide to zinc oxide in the oxide film on the surface is
It is in the range of 0.5 to 2.0, and it is not always easy to control the molar ratio of aluminum oxide to zinc oxide in the coating to 0.5 or less.

[0007] Such a joining technique of a plated steel sheet using an adhesive has a relatively new demand, and therefore has a good adhesive joining property and a good chemical conversion treatment property. No satisfactory plated steel sheet has been developed yet.

[0008]

SUMMARY OF THE INVENTION The present invention relates to a zinc-based hot-dip galvanized steel sheet which has been demanded as such a rust-proof steel sheet for automobiles and the like, has good performance such as corrosion resistance and has excellent adhesive bonding properties. The manufacturing method is provided.

[0009]

Means for Solving the Problems The inventors of the present invention have conducted various studies on hot-dip galvanized steel sheets, mainly using a soft synthetic rubber-based adhesive, and concerning factors for improving the adhesiveness. First, in order to make the surface stable against adhesion, the surface was cleaned and examined for its effect, but the adhesion was not always good. This is because the cleaned metal surface does not have good wettability of the adhesive, so that not only the mechanical anchoring effect is not sufficiently exerted, but also factors that generate chemical attraction such as hydrogen bonding on the metal side. It was thought that it was enough.

[0010] Next, a method of forming an oxide film by oxidizing the surface under controlled conditions after cleaning was examined. However, if the oxidation is slight, even if the adhesion is improved, the oxidation proceeds. Decreases. This was presumed to be because the wettability of aluminum oxide was not as good as that of zinc oxide.

In a hot-dip galvanized steel sheet, the presence of aluminum in the plating layer is inevitable for stable production of the plating even if it is not zinc-aluminum alloy plating. The aluminum contained in the plated zinc, even in small amounts, is selectively oxidized on the plating surface in an oxidizing atmosphere, such as in the air, whereby it diffuses from the inside and thickens, and the oxide film or electrode The amount of aluminum oxide in the surface layer increases.

Therefore, in consideration of the fact that aluminum is concentrated in the extreme surface layer, various studies were made on a method for improving the adhesiveness. As a result, it was found that if the aluminum oxide in the extreme surface layer was replaced with aluminum hydroxide, the adhesiveness was greatly improved, and the present invention was reached.

The gist of the present invention is as follows: (1) Thickness of plating surface 1
A hot-dip galvanized steel sheet with excellent adhesive bonding properties, characterized in that aluminum hydroxide is present in the surface layer of up to 5 nm in a molar fraction of at least 10% with respect to other compounds, and
(2) a method for producing a hot-dip galvanized steel sheet having excellent adhesive bondability, characterized by forming the extreme surface layer according to (1) on the surface of the plating by treating with high-temperature steam,
It is.

Here, the extreme surface layer means a thin layer made of a nonmetallic compound such as an oxide, which covers the surface of the plating, which cannot be detected by optical microscopic observation of the cross section. Of saturated steam.

[0015]

The hot-dip galvanized steel sheet used as the base material of the present invention is:
Hot-dip galvanized steel sheet, alloyed hot-dip galvanized steel sheet, hot-dip zinc-aluminum alloy coated steel sheet, and the like. The extreme surface layer made of a non-metallic compound on the plating surface of these steel sheets has a thickness of 1 to 5 nm, and the adhesiveness is improved if aluminum hydroxide of 10% or more is present in the extreme surface layer by mole fraction. Is done.

When the thickness of the extreme surface layer is less than 1 nm, there are portions where the metal (plating layer) is exposed, and the wettability is poor and the adhesive strength is insufficient. On the other hand, when the thickness exceeds 5 nm, not only the extreme surface layer is destroyed when stress is applied, and the adhesive strength is lowered, but also the chemical conversion property at the time of coating on the plating may be deteriorated. Compounds other than aluminum hydroxide in the extreme surface layer may include, in addition to hydroxides and oxides, phosphates, borates, silicates, heavy metal oxyacid salts, and the like. 10% by mole fraction of aluminum hydroxide in the extreme surface layer consisting of
If it is above, the adhesive strength is improved, and if it is less than 10%, the improvement effect is not exhibited. The composition of the extreme surface layer can be analyzed by applying photoelectron spectroscopy (XPS) or the like.

Although the reason why the presence of aluminum hydroxide improves the adhesive bonding property is not fully understood, since hydroxyl groups are present as compared with aluminum oxide which is usually contained in a large amount,
It is conceivable that the wettability is improved, and that hydrogen bonds related to the adhesive strength are easily formed.

As a method for stably obtaining such a hot-dip galvanized steel sheet in which aluminum hydroxide is present, first, for example, a cleaning method of degreasing a raw steel sheet with an alkaline solution and removing a surface oxide simultaneously with an alkaline solution, The surface is cleaned by a method of mechanically removing the surface layer such as grinding. However, when a clean state immediately after plating is maintained, cleaning is not particularly required. Next, steam is sprayed on the steel sheet to form aluminum hydroxide. In this case, the temperature of the steam is desirably set to 150 to 350 ° C (saturated steam). It is desirable to set the holding time to 0 to 10 s.

The cleaning of the surface before the steam treatment is intended to obtain a stable adhesive strength by reducing the compound species other than aluminum hydroxide remaining on the surface. If the temperature of the steam treatment is too low, the production of aluminum hydroxide is too small to obtain sufficient adhesive strength, and if the temperature is too high and the time is too long, the surface layer becomes too thick and the adhesive bondability is deteriorated. Instead, the iron-zinc alloy layer of the plating layer may develop excessively and lose the integrity of the plating.

As described above, the method for improving the adhesive bonding property of the present invention can be carried out quickly and simply, and can be realized, for example, by installing a simple steam treatment facility in a production line of a hot-dip galvanized steel sheet. it can.

[0021]

[Example] Plating weight of about 40 manufactured under general conditions
A hot-dip galvanized steel sheet, a galvannealed hot-dip galvanized steel sheet, and a hot-dip galvanized-5% aluminum alloy-plated steel sheet having a thickness of 1 g / m ² and a thickness of 1 mm were prepared. After cleaning the surface with an alkaline solution, water vapor at 200 ° C. was irradiated with water vapor to form aluminum hydroxide on the surface. In this case, the treatment time was changed to change the thickness of the extreme surface layer and the mole fraction of aluminum hydroxide. The mole fraction was measured using XPS. Table 1 shows the results of the analysis of the steam treatment time, the thickness of the extreme surface layer, and the foundation.

[0022]

[Table 1]

A test piece having a width of 25 mm and a length of 150 mm was cut out from the plated steel sheet in which aluminum hydroxide was formed on the extreme surface layer, and an adhesive strength test was performed by a T-peeling method. In this case, a commercially available soft synthetic rubber-based adhesive (trade name: Sunstar Giken E6045) was used as the adhesive, the chuck portion in the peel test was 50 mm, the length of the bonded portion was 100 mm, and the thickness of the adhesive was 0.15. A spacer was provided so as to be mm and bonded.
After overlapping and pressing, they were baked and cured in an oven heated to 165 ° C. for 25 minutes.

The test results are also shown in Table 1. However, factors other than the adhesive strength at the interface between the adhesive and the steel sheet are added to the bonding strength. Good adhesion (○ mark) when broken inside the agent (cohesion failure), poor adhesion (× mark) when the entire surface peels off at the interface between the adhesive and the steel sheet (x mark) The case where peeling was mixed was indicated as slightly good adhesiveness (marked with △).

As is apparent from these results, when aluminum hydroxide is present in the surface layer of the plating at a molar fraction of 10% or more, peeling between the adhesive and the interface is not recognized, and the adhesive bonding is not performed. It can be seen that the properties are good.

[0026]

The hot-dip galvanized steel sheet of the present invention has excellent adhesive bonding properties and is suitable as a rust-preventing steel sheet used for automobiles and home electric appliances. Also, the manufacturing method of the steel sheet is
Quick, simple, and easy to implement.

Continuation of the front page (56) References JP-A-4-131386 (JP, A) JP-A-3-146648 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) C23C 2 / 00-2/40

Claims (2)

(57) [Claims] An aluminum alloy having a thickness of 1 to 5 nm on the surface of a plating surface, wherein aluminum hydroxide is present in a molar fraction of 10% or more with respect to other compounds. Galvanized steel sheet. 2. A method for producing a hot-dip galvanized steel sheet having excellent adhesive bonding properties, wherein the extreme surface layer according to claim 1 is formed on the surface of the plating by treating with high-temperature steam.