JPH02163400A - Composition zn plated material - Google Patents

Abstract

PURPOSE:To produce a composite Zn plated material having satisfactory adhesion of the plating layer, superior press formability and corrosion resistance by forming a Zn plating layer contg. an acrylamide polymer on the surface of a metallic base material under specified conditions. CONSTITUTION:An acrylamide polymer and/or a methacrylamide polymer contg. 120-200mol% N-methylol groups per one monomeric unit is added to a Zn plating bath by 0.001-10wt.% and the surface of a metallic base material is electroplated with the bath to form about 1-40g/m<2> Zn plating layer contg. the polymer. In the plating layer, (002) crystal faces as bottoms are preferentially oriented, the crystal structure is made dense and the plating layer has superior corrosion resistance.

Description

Detailed Description of the Invention [Field of Application in Industry A] The present invention provides a coating film that has good adhesion of the plating layer, has excellent press formability and corrosion resistance, and has excellent coating film properties without any pre-painting treatment. The present invention relates to a Zn-based plating material that can provide good adhesion, and is useful for outer panels of automobiles, vehicles, household electrical appliances, and the like.

[Conventional technology].

Zn-plated materials, which are made by applying Zn gloss to steel plates, have good corrosion resistance and have been used in a wide range of applications, including automobiles, household electrical appliances, and construction materials.

However, as the technology becomes more sophisticated and the demands of users become more stringent, the corrosion resistance of Zn and % plated materials is also required to be even higher. Conventionally, measures have been taken to meet these demands, such as (a) increasing the amount of plating deposited (c) adopting Zn-based alloy plating such as Zn-Ni or Zn-Fe.

[Problems to be Solved by the Invention] However, in the method (A') above, as the amount of plating increases, a phenomenon in which the plating layer adheres to the mold during press molding (build-up phenomenon) occurs, In addition, in the method (b) above, since the alloy plating layer is hard, the plating layer peels off during press forming (bacterial phenomenon), and in the end, both methods (() and (b) are difficult to press. There was a problem that moldability was impaired.

Furthermore, when using plated materials for parts such as automobiles and home appliances, it is common to apply a coating, but Zn
Since the coating film adhesion of the surface to which system plating has been applied is insufficient, it is necessary to perform IA filling using phosphates, chromates, etc. before painting, which tends to make the process complicated.

The present invention was made in view of these circumstances, and its purpose is to provide excellent press formability without causing build-up or powdering phenomena during press molding, and to eliminate pre-painting treatment. An object of the present invention is to provide a Zn-based plated material that can provide excellent paint adhesion without carrying out any steps.

[Means for Solving the Problems] The structure of the present invention that can solve the above problems is that one N-methylol group per monomer unit is added to the surface of the metal base material.
Acrylamide containing 20 to 200 mol% and/or
Or methacrylamide polymer from 0.001 to 10
! The gist is that a Zn-plated layer is formed which contains Zn in an amount of % i and the remainder is made of Zn or a Zn alloy preferentially oriented in the crystal bottom (002) plane.

[Function] The present inventors have investigated the cause of the poor press formability of conventional Zn-plated materials and Zn alloy-plated materials, and have obtained the following knowledge. In other words, in conventional Zn-based plating, poor lubricity on the plating surface causes build-up, and in Zn alloy plating such as Zn-Ni and Zn-Fe, the plating layer is hard. It was thought that the hardness was too different from that of the plating base material, causing powdering.

Therefore, we investigated ways to improve the lubricity of Zn plating and the hardness of the Zn-based alloy plating layer, and found that if the plating layer contained an organic polymer, the lubricity would be excellent, and the hardness of the plating layer would also be lower than normal. It was found that the hardness was approximately Hv 100 to 200, which was almost similar to the hardness of the plating base material used, and that the press formability of the plated material could be improved.

We also investigated paintability and found that if polar groups are present on the surface of the plating layer, hydrogen bonds will occur between the surface of the plating layer and the coating film due to the action of the polar groups, resulting in excellent coating properties even without pre-treatment. It was concluded that membrane adhesion could be obtained. As a result of further research based on these findings, we found that among organic polymers, N-methylolacrylamide units or N-
- 10 to 70 mol% of methylol methacrylamide units
An acrylamide-based or methacrylamide-based polymer (hereinafter referred to as an AM-based polymer) containing an amount of 0.001 to 10% is used in a Zn-based plating layer made of Zn or a Zn alloy. It was confirmed that the press formability and paintability were significantly improved by containing about % i, and a patent application was previously filed (Japanese Patent Application No. 258115/1983, unpublished).

However, as I continued my research further, I discovered that AM-? The N-methylol modification amount of the t-polymer does not necessarily show a good effect only in the range of 10 to 70 mol%, but when the modification amount is increased to 120 to 200 mol%, this polymer is blended in an amount of 'a. It was revealed that the paintability (coating film adhesion) and corrosion resistance (corrosion resistance after coating) of the Zn-based plating material were much better, and the press formability was also very excellent. That is, in the prior invention, the paintability and press formability of the Zn-based plating material are the same as the N-
The amount of methylol modification shows a peak in the range of 10 to 70 mol%, and if the amount of modification exceeds 70%, the stability of the polymer in the plating bath decreases, so the effect of adding AM polymer tends to decrease. We believe that it indicates
In fact, the effect of improving paintability, etc. in the modification amount range of 70 to 120 mol% is worse than that in the modification amount range of 10 to 70 mol%. However, when the amount of N-methylol modification is increased to 100 mol% or more, the improvement effect increases again, and when the amount of modification is 120 to 200 mol%, both paintability and corrosion resistance (removability of the paint film after painting) are 10 to 10%. The improvement effect exceeds that of the 70 mol% modified product.

For example, Figure 1.2 is a graph showing the relationship between the amount of N-methylol modification of AM-based polymers, paintability (coating 11i adhesion) and corrosion resistance (paint peelability), and the experimental conditions were as follows. be.

Plating layer composition: Zn ten-modified AM polymer 1% by weight Plating amount: 20 g/m2 Top coat: Melamine modified alkyd resin paint (20μ
m) Paintability: Calculated from the amount of paint film removed by tape peeling when the painted material was subjected to the Erichsen test on the substrate Corrosion resistance: When the painted material was subjected to the salt spray test after cross-cutting, and the tape was peeled off 24 hours later. Calculated based on the peeling width of the coating film As is clear from Figure 1, the paintability showed good results when the amount of N-methylol modification was in the range of 10 to 70 mol%, but slightly decreased when the amount of N-methylol modification was in the range of 70 to 120 mol%. It gets worse, but 120
When the mol% is exceeded, excellent coating properties are again exhibited. Furthermore, as is clear from Figure 2, the corrosion resistance is better when the N-methylol modification amount is 120 to 200 mol%.
It is confirmed that it is superior to that of 70 mol%.

These effects are due to the hydrogen bonding force based on the large polarity of the methylol groups present in large amounts in the AM tea-based polymer, as well as the polycondensation reaction that occurs between the methylol groups and the coating film components during paint baking, which improves the adhesion of the paint film. This is thought to be due to further improvement in corrosion resistance.

Furthermore, when electrolytic plating is performed by adding AM-based polymer with a high methylol modification amount to a Zn-based plating bath, Zn
A Zn-based plating layer is formed in which the crystal bottom plane [especially the (002) plane] is preferentially oriented, which is said to have excellent corrosion resistance among the Zn-based platings, and the crystal structure also becomes denser, further improving the corrosion resistance of the plating layer. It will be excellent. For example, Fig. 3 (A), ([1) shows ZnJl, self-plated FI
[Figure 3 (B)] and a Zn-based plating layer containing 11% by weight of N-methylol modified AM polymer [Figure 3 (A)]
It can be confirmed that the (002) plane of Zn is preferentially oriented in the plating layer of the present invention (the latter).

Next, Figure 4 shows the coating film peeling rate by the base Erichsen test of the melamine-modified alkyd resin paint coating material and the drobead test of the plating material for samples prepared with various modified AM-based polymer contents in the plating layer. This figure shows the results of measuring the amount of plating peeled off afterwards. However, the N-methylol modification amount of the modified AM polymer used was 140 mol%, and the thickness of the plating layer was 40 g/rn2.

As is clear from Figure 4, modified AM in the plating layer
When the content of the system polymer is less than 0.0011i%, there is little improvement in both press formability and paintability; on the other hand, 10! When the amount exceeds i%, there is no adverse effect on the paintability (!!! film adhesion), but the plating layer becomes brittle and bacterium tends to occur.

From this point of view, the content of modified AM polymer should be 0.
The content must be set in the range of 0.001 to 10% by weight, and the effect is more reliably exhibited in the range of 0.5 to 5% by weight. Incidentally, when the amount of methylol modification is increased, the plating performance is improved, but since the activity of the polymer itself is also improved, stability in the plating bath may become a problem. Under normal plating bath conditions, this is not a particular problem, but if necessary, adding an appropriate amount of an appropriate stabilizer depending on the plating bath to prepare the plating will not affect the plating performance in any way. It's not a thing.

As mentioned above, in the present invention, Zn-based alloys can be used in addition to Zn from the viewpoint of improving corrosion resistance, but the most common alloying elements used are Ni, Co, and C.
r, Mn, etc., and these alloying elements may be used alone or in combination with 2f! A combination of the above components is usually added in a range of 3 to 20% by weight in Zn.

Although the amount of plated coating is not particularly specified, if it is less than 1 g/m', it is difficult to sufficiently coat the surface of the substrate, while if it exceeds 40 geQ+2, no further effect in terms of corrosion resistance etc. can be obtained. On the contrary, press formability tends to deteriorate. Therefore, the coating weight is preferably in the range of 1 to 40 g/m'.

Next, the plating base material used in the present invention is steel, A1
, Cu, and other metals and alloys that can be plated, and the shape may be plate-like, rod-like, tubular, irregularly shaped, etc. In addition, Zn or Z is added to these base materials.
A base material that has been subjected to n-alloy plating (electroplating, hot-dip plating, alloyed hot-dip plating, vapor deposition plating, etc.) is used, and the above-mentioned modified AM-based polymer-containing Zn-based plating is applied to this surface to form multilayer plating. It is also possible to do this.

The plating method is also not particularly limited, but the most common is electroplating, for example, consisting of an aqueous solution containing Zn ions (in the case of alloy plating, containing metal ions as alloying elements) and N-methylol-modified AM-based polymer. A method is adopted in which a plated base material whose surface has been purified by degreasing, pickling, etc. is immersed in an electroplating bath and electrolyzed. In this case, if the concentration is adjusted so that the N-methylol-modified AM polymer content in the electroplating ranges from 0.1 to 0.1, a plated layer with the desired composition shown above can be obtained. easy.

Next, the present invention will be explained in more detail with reference to Examples.
The present invention is of course not limited by the following examples, and any modification and implementation as appropriate within the scope of the above and below-mentioned spirit is within the technical scope of the present invention.

[Example] A cold-rolled steel sheet that had been pretreated by degreasing and pickling was subjected to the following electroplating treatment. That is, a predetermined N-methylol-modified AM polymer was added to a Zn plating bath or a Zn alloy plating bath, and electroplating was performed to form a plated layer having the composition shown in Table 1. The coating weight was 20 g/m'' in each case.The coatability, corrosion resistance, and press formability of each of the obtained galvanized steel sheets were examined using the following methods, and the results shown in Table 1 were obtained. Ta.

Paintability: A melamine-modified alkyd resin paint was applied directly to a galvanized steel plate to a film thickness of about 20 μm, and after baking was treated, the paint film peeling rate was determined by the degree of tape peeling according to the Erichsen test.

O: Paint film peeling rate 5% or less ○: 〃 5-15% △; 〃 15-30% After 24 hours, the cross-cut portion was peeled off with a tape, and the width of the coating film peeled off was determined.

◎: Coating film peeling width 101111 or less O: 〃 1-2 mm Δ: 〃 2-5■ X: // 5 mm or more Press formability: A plated steel plate was subjected to a drobead test, and the plating l! lJl! The quantity was evaluated.

◎: Plating peeling amount 0.5 g/m2 or less 0: NO, 5-0.8 g/m'△:
/7 0.8-1.5g/m2X: n
1.5g/m" From Table 1, it can be considered as follows.

Experiment Nos. 1 to 5 are all examples that satisfy the specified requirements of the present invention, and good results were obtained in all aspects of paintability, corrosion resistance, and press formability.

On the other hand, Experiment No. 8 is a comparative example consisting of a Znn paddy layer, and both performances are poor.

Moreover, Experiment Nos. 7 and 10 are comparative examples in which the polymer content in the plating layer is insufficient, and the performance of all of them is insufficient. Experiments Nos. 9 and 11 are comparative examples in which the amount of N-methylol modification in the polymer is insufficient, and all three performances are insufficient. Furthermore, Experiment No. 8 is a comparative example in which the polymer content in the plating layer exceeds the specified range, and although the paintability is good, the plating layer becomes somewhat brittle, resulting in poor press formability and poor corrosion resistance. .

[Effects of the Invention] The present invention is configured as described above, and includes AM having a specified amount of N-methylol modification in the Zn or Zn alloy plating layer.
By containing an appropriate amount of a type polymer, it has excellent moldability and adhesion without causing build-up or bactering phenomena during the press molding process, and exhibits excellent corrosion resistance, and can be coated without pre-painting treatment. It has now become possible to provide a Zn-based plated material that exhibits good coating film adhesion.

[Brief explanation of the drawing]

Figure 1.2 is a graph showing the relationship between the N-methylol modification amount of AM-based polymer, coating peeling rate, and coating peeling width, Figure 3 is an X-ray diffraction chart of the plated layer, and Figure 4 is the inside of the plated layer. It is a graph which shows the relationship between N-methylol modified AM type polymer content and coating film peeling rate.

Claims (1)

[Claims] 0.001 to 0.001 to 0.001 to methacrylamide based polymer containing 120 to 200 mol% of N-methylol groups per monomer unit on the surface of the metal base material.
10% by weight of a Zn-based plated material, characterized in that a Zn-plated layer is formed thereon, the remainder being Zn or Zn alloy with preferential orientation of the crystal bottom (002) plane.