JPH06240490A - Corrosion resistant chromium plating - Google Patents

Abstract

PURPOSE:To produce decorative Cr plating excellent in corrosion resistance. CONSTITUTION:Plating is carried out with an Ni-P alloy contg. 8-15wt.% P to form a substrate in 5-20mum thickness and then Cr plating is formed. Even when the Ni-P alloy plating is exposed through a flaw or crack in the Cr plating, a condensed layer of P is formed simultaneously with the beginning of dissolution of the Ni-P alloy plating due to the formation of a local cell and passivation is caused. Since the electromotive force of the local cell is vanished by the passivation and corrosion is stopped, the corrosion resistance of the Cr plating is remakably improved.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to decorative chrome plating applied to the surface of automobiles, electric appliances, or parts thereof.

[0002]

2. Description of the Related Art Chromium plating has a beautiful metallic luster with a bluish tint, and this luster is extremely stable in the atmosphere and does not fog or discolor. For this reason, decorative chromium plating, which enhances corrosion resistance and decorative effect by applying copper-nickel-chromium or nickel-chromium plating to the surface of automobiles, electric products, or parts thereof, is often used.

In the decorative chrome plating step, the following has been conventionally used. Base-Copper plating-Bright nickel plating-Chromium plating Then, the bright plating not only provides a bright electrodeposition on the plated surface, but also has a smoothing action to reduce the roughness of the base or the underlying plated surface.

However, these copper-nickel-chromium or nickel-chromium plating forms a local battery due to flaws or cracks in the chromium plating film to cause corrosion, resulting in corrosion of the base material and not only poor appearance but also product. Could be a fatal flaw in the. In particular, since bright nickel plating contains sulfur in electrodeposited nickel, it has a lower potential and poorer corrosion resistance than nickel that does not contain sulfur. I will end up.

Therefore, conventionally, a method has been adopted in which the thickness of each plating layer is increased, the plating layers are multilayered, or the chromium plating layer is provided with microcracks or micropores to disperse local batteries in advance. There is.

[0006] For example, the two-layer nickel plating is a bright nickel plating containing sulfur (0.05%) on semi-bright nickel that does not contain sulfur. The bright plating containing sulfur becomes a semi-bright plating in a corrosive environment. On the other hand, it works as an anode and the corrosion reaction stops at the bright nickel plating layer, so it has good corrosion resistance.

The microcrack chrome is a decorative chrome with fine cracks, and has the effect of dispersing the corrosion points generated by the fine cracks, preventing the concentration of the corrosion, and preventing the corrosion of deep areas. . The microporous chrome plating is to improve the corrosion resistance by generating a large number of minute holes in the chrome plating to disperse the corrosion.

As an example of the microporous chrome plating, there is an invention of Japanese Patent Publication No. 56-15471. In this invention, insoluble fine particles are dispersed in the nickel plating which is a lower layer of the chrome plating, and When chromium plating is performed on the non-metallic particles, the non-metallic particles are not plated with chromium, so that many holes are generated in the chromium plating.

[0009]

However, in the two-layer nickel plating, the bright nickel plating layer serves as a sacrificial anode and the corrosion spreads laterally. Corrosion holes eventually penetrate the semi-bright plating layer and reach the substrate. , Microcrack chrome is a special nickel stripe plating with high stress on bright nickel plating to generate uniform cracks on chrome plating with high stress of nickel, but on the contrary, unless the thickness and stress of nickel are strictly controlled. Corrosion resistance decreases.
In addition, the microporous chrome plating has a drawback in that once a flaw is formed, a large amount of corrosion occurs from there. In addition, the fine particles are dispersed so that the micropores are uniformly generated,
It is required to control it so that it will co-deposit with nickel.If it is not strictly controlled, uneven appearance will occur due to uneven gloss due to the non-uniform amount of eutectoid, and corrosion resistance will be a problem due to partial corrosion. It was

The present invention has been made in order to solve the above-mentioned problems of decorative chromium plating, and has corrosion resistance without complicated steps and without requiring complicated management of the underlayer. It is an object of the present invention to provide a corrosion-resistant chromium plating that can obtain an excellent plating layer.

[0011]

Means for Solving the Problems The present inventors have noticed that nickel-phosphorus alloy plating has excellent corrosion resistance, and have conceived that this nickel-phosphorus alloy plating is used as an underlayer plating of chromium plating. Then, as a result of further intensive studies on the relationship between the phosphorus content and the plating thickness and the corrosion resistance in the nickel-phosphorus alloy plating, it was found that the corrosion resistance is remarkably improved by setting the predetermined plating thickness at the predetermined phosphorus content. To complete the present invention.

The corrosion-resistant chromium plating of the present invention contains phosphorus of 8%.
The gist is that a nickel-phosphorus alloy containing ˜15 wt% is plated as a base layer for 5 to 20 μm and then chrome plated. Furthermore, the gist is that semi-bright nickel plating and bright nickel plating are sequentially formed as an underlayer of the nickel-phosphorus plating, if necessary.

For the nickel-phosphorus alloy plating of the underlayer, either electroplating or electroless plating may be used. The phosphorus content of the plating layer formed by nickel-phosphorus alloy plating varies widely depending on the production conditions such as bath composition, pH, and electrolysis conditions.
These generation conditions are appropriately selected so as to be ˜15%.

By controlling the phosphorus content of the nickel-phosphorus alloy plating layer to 8% or more, the film forms a passivation film and becomes a film excellent in corrosion resistance. That is, the phosphorus content is 8
It should be -15%. This is because if the phosphorus content is less than 8%, the corrosion resistance is not effective and it is the same as that of ordinary nickel plating. If the phosphorus content exceeds 15%, the corrosion resistance is excellent, but the electrodeposition rate decreases and bath management , Because it is difficult to work and is not practical.

The thickness of the nickel-phosphorus alloy plating layer must be 5 to 20 μm. By setting the thickness of the plating layer to 5 μm or more, defects that occur in the plating film are prevented and the film has excellent corrosion resistance. If the plating thickness is less than 5 μm, the corrosion resistance deteriorates, and if the thickness exceeds 20 μm, the plating becomes cloudy and unsuitable for decorative purposes.

When nickel-phosphorus alloy plating is applied to the underlayer, fine particles are dispersed and plated in a plating bath, and a large number of micropores are intentionally formed in the chromium plating layer plated on the underlayer. Thus, by dispersing the corrosion caused by the local battery, the corrosion resistance of the plating layer can be further improved.

For the chrome plating, a commonly used decorative chrome plating bath can be used. The thickness of the chrome plating needs to be 0.05 μm or more depending on the required scratch resistance and the like, but if the plating thickness exceeds 3 μm, the appearance is poor such as gray and kogation, which is not suitable for decorative purposes. If a passivation film is formed on the nickel-phosphorus alloy plating film, the chrome plating will not be evenly deposited and will be gray, making it difficult to use for decorative purposes. desirable.

According to the present invention, the corrosion resistance is ensured by nickel-phosphorus alloy plating, and the chromium plating is used to secure the scratch resistance and the chrome color, and the decorative chromium plating film excellent in corrosion resistance is formed. Nickel-phosphorus alloy plating is characterized by hardness, wear resistance, magnetism, and chemical resistance, and is utilized for plating cylinders, drum can-making materials, etc. by making the most of these characteristics.

[0019]

[Function] In the conventional plating method, a local battery is configured in advance,
It is a corrosion-dispersion type corrosion-resistant plating film that disperses electromotive force and suppresses the progress of corrosion. Even if a local battery is formed by scratches or cracks in the chromium plating, it has little effect. Corrosion is Figure 2
As shown in the cross-sectional view of, by the electrolytic reaction from the porous portion,
Dissolution starts from bright nickel with a low potential, but since the electromotive force is small, the corrosion current density is also small and the dissolution is slow.

According to the plating method of the present invention, even if the nickel-phosphorus alloy plating film is exposed due to scratches or cracks in the chromium plating, the nickel-phosphorus alloy film can form a local battery as shown in the sectional view of FIG. At the same time as the melting starts, a phosphorus condensed layer is formed and passivation occurs, the electromotive force of the local battery disappears, and the corrosion stops. As described above, the present invention is a plating method in which the electromotive force of the local battery is not dispersed by corrosion but by corrosion inhibition by passivation, and the corrosion resistance is significantly improved.

[0021]

EXAMPLES Examples of the present invention will be described in comparison with comparative examples,
The effect of the present invention will be clarified. (Example 1) An ABS resin was used as a raw material, electroless nickel plating was applied thereto, and then electroplating was performed as Example 1 of the present invention by the following method. Acid immersion Liquid composition Sulfuric acid 25-80 g / l Bath temperature Room temperature Immersion 5 seconds to 1 minute Rinse with water

Copper Strike Plating Liquid Composition Copper Pyrophosphate Trihydrate 15-25 g / l Potassium Pyrophosphate 60-100 g / l Potassium Oxalate 10-15 g / l P Ratio 11-13 Bath Temperature 40-50 ° C. PH 8-9 Cathode current density 1-5A / dm ² Stirring Air stirring Water washing

Acid immersion Liquid composition Sulfuric acid 30 to 60 g / l Bath temperature Room temperature Immersion 5 seconds to 1 minute

Copper plating solution composition Copper sulfate pentahydrate 150 to 200 g / l Sulfuric acid 50 to 90 g / l Hydrochloric acid 40 to 100 g / l Brightening agent (thiourea) 3 to 7 ml / l Brightening agent (dextrin) 0.5 to 1 ml / L Bath temperature 15 to 25 ° C Cathode current density 1 to 5 A / dm ² Stirring Air stirring Water washing

Acid immersion Liquid composition Hydrochloric acid 5 to 10 g / l Bath temperature Room temperature Immersion 30 seconds to 1 minute Rinsing with water

Semi-bright nickel plating solution composition Nickel sulfate hexahydrate 250 to 350 g / l Nickel chloride hexahydrate 35 to 50 g / l Boric acid 30 to 60 g / l Brightening agent (sodium naphthalenedisulfonate) 0.1 0.2g / l Liquid temperature 40-60 ° C PH 3.5-4.5 Cathode current density 1-5A / dm ² Stirring Air stirring

Bright Nickel Plating Liquid Composition Nickel Sulfate Hexahydrate 250-360 g / l Nickel Chloride Hexahydrate 35-60 g / l Boric Acid 30-50 g / l Brightening Agent (5-Naphthalenedisulfonate Sodium) 5-40 g / l Brightener (2-butyne-1,4-diol) 0.1 to 10 g / l Liquid temperature 40 to 60 ° C PH 3.5 to 4.5 Cathode current density 1 to 5 A / dm ² Stirring Air stirring Water washing

Phosphorus-nickel alloy plating solution composition Nickel sulfate hexahydrate 180 to 220 g / l Nickel chloride hexahydrate 70 to 90 g / l Additive (phosphorus compound) 200 to 250 cc / l Bath temperature 55 to 65 ° C. PH 0. 5 to 1.5 Cathode current density 3 to 10 A / dm ² Stirring Air stirring Water washing

Chromium plating solution composition Chromic anhydride 150 to 400 g / l Sulfuric acid 0.5 to 4 g / l Fluorosilicate 0.5 to 10 g / l Bath temperature 35 to 55 ° C. Cathode current density 5 to 25 A / dm ² Washing with water The obtained plating film was a standard two-layer plating, and the appearance was equivalent to or better than the conventional one.

Example 2 An ABS resin was used as a raw material, electroless nickel plating was applied thereto, and then the steps of Example 1 were omitted, and electroplating was performed as Example 2 of the present invention. In this example, the semi-bright nickel plating was omitted, but the appearance of the plating film was the same as the conventional one.

(Embodiment 3) Using an iron material as a raw material, electroplating was carried out as a third embodiment of the present invention in the steps 1 to 3. In this example, an iron material was used as the raw material, but the appearance of the plating film was comparable to that of the conventional one.

Example 4 An ABS resin was used as a raw material, electroless nickel plating was applied thereto, and then electroplating was performed as Example 4 of the present invention by using the same steps as in Example 1. However, plating was performed by adding inorganic fine particles to the liquid composition of the process as shown below. 'Phosphorus-nickel alloy plating solution composition Nickel sulfate hexahydrate 180-220 g / l Nickel chloride hexahydrate 70-90 g / l Aluminum oxide 10-15 g / l Additive (phosphorus compound) 200-250 cc / l Bath temperature 55-55 65 ° C. PH 0.5 to 1.5 Cathode current density 3 to 10 A / dm ² Stirring Air stirring Washing with water In this example, fine particles are dispersed in a plating bath for plating, and the chromium plating layer plated on this underlayer is conscious. Although a large number of micropores were generated to further improve the corrosion resistance, the obtained plated film had a slight loss of gloss, but it was within the range.

Example 5 After the steps of Example 2, the following nickel plating was applied, and then chromium plating was applied thereon. Liquid composition nickel sulfate hexahydrate 250 to 360 g / l nickel chloride hexahydrate 35 to 60 g / l boric acid 30 to 50 g / l inorganic fine particles 15 to 20 g / l brightener (2-butyne-1,4 diol) 0. 1 to 10 g / l Bath temperature 40 to 60 ° C. PH 3.5 to 4.5 Cathode current density 1 to 5 A / dm ^{2 In} this example, fine particles are dispersed and plated in a plating bath, and this underlayer is plated. The chrome plating layer was intentionally formed with a large number of micropores to further improve the corrosion resistance, but the obtained plating film had a slight loss of gloss, but it was within the range.

(Evaluation of Corrosion Resistance) According to Examples 1 and 3, copper plating, semi-bright nickel plating, bright nickel plating, nickel-phosphorus alloy plating, and chrome plating were plated as the film thicknesses shown in Table 1. . The thickness of the nickel-phosphorus alloy plating was 5 μm in all cases,
In the comparative example, the underlayer was the same as in Example 1 and the nickel-phosphorus alloy plating layer was 2 μm. Corrosion resistance of the obtained plating film was evaluated according to Japanese Industrial Standard JIS D0201 "General rules for electroplating of automobile parts", Annex 1, Corrode coat test, and Annex 2, Cass test. For comparison, as a conventional example, a sample plated according to Example 3 (d) of Japanese Patent Publication No. 56-15471 was evaluated for corrosion resistance by the same method. In this conventional example, the nickel-phosphorus alloy plating was fine particle dispersed nickel plating.
The obtained evaluation results are summarized in Table 1 as a latency number.

[0035]

[Table 1]

In Table 1, Cu: copper plating SNi: semi-bright nickel plating BNi: bright nickel plating alloy: nickel-phosphorus alloy plating (fine particle dispersed nickel plating in the conventional example) Cr: chromium plating. The corrode coat test was conducted for 3 cycles and the cast test was conducted for 200 hours.

As shown in Table 1, the comparative example is nickel-
Since the thickness of the phosphorus alloy plating layer was as thin as 2 μm, the latency number in the corrode coat test was 6.0 and the latency number in the cass test was 6.5, and the corrosion resistance was poor. In the conventional example, the latency number in the corrode coat test was 8.0, which was a high value, but the latency number in the cass test was 6 or less, and the corrosion resistance was poor.

On the other hand, in Examples 1 and 3 of the present invention, since the nickel-phosphorus alloy plating layer had a thickness of 5 μm, it had sufficient corrosion resistance and no nickel-phosphorus alloy plating layer was formed. By mobilization, the latency numbers of the corrode coat test were 9.0 and 8.0, and the latency numbers of the cass test were 9.8 and 8.0, confirming the effect of the present invention. .

Next, according to the plating process shown in Example 1, the phosphorus content of the nickel-phosphorus alloy plating layer was varied between 0 and 25% with the film thickness shown in Table 1 to form a plating film. Formed. When the corrosion resistance and the electrodeposition rate of the formed plating film were evaluated, the results shown in FIG. 3 were obtained.
The evaluation criteria of corrosion resistance are indicated by ○, △, ×, ○ indicates no change in appearance (latency number 9.8 to 10), and △ indicates change in appearance but not so noticeable (latency number 8 ~ 9.0), x is a problem in appearance and quality (latency number 5 or less).

As shown in FIG. 3, it was found that when the phosphorus content of the nickel-phosphorus alloy plating layer was less than 8%, the corrosion resistance deteriorated sharply. It was also found that when the phosphorus content of the nickel-phosphorus alloy plating layer exceeds 15%, the electrodeposition rate sharply decreases. As a result, nickel
It was confirmed that the best results were obtained by setting the phosphorus content of the phosphorus alloy plating layer to 8 to 15%.

Then, according to the plating process shown in Example 1, the film thickness of the nickel-phosphorus alloy plating layer was changed from 0 to 25 μm to form a plating film with the film thickness shown in Table 1. . When the corrosion resistance and appearance of the formed plating film were evaluated, the results shown in FIG. 4 were obtained.

As shown in FIG. 4, it was found that when the thickness of the nickel-phosphorus alloy plated layer was less than 5 μm, the corrosion resistance deteriorated sharply, and when the thickness exceeded 20 μm, the appearance deteriorated. The thickness of the phosphorus alloy plating layer is 5 to 20
It was confirmed that the best result was obtained by setting the thickness to μm.

[0043]

As described above in detail, the corrosion-resistant chromium plating of the present invention is performed by plating the nickel-phosphorus alloy containing 8 to 15% by weight of phosphorus as an underlayer for 5 to 20 μm and then performing the chromium plating. The feature is that even if the nickel-phosphorus alloy plating film is exposed due to scratches or cracks in the chromium plating, the nickel-phosphorus alloy film begins to dissolve in the formation of the local battery and at the same time a phosphorus condensation layer is formed. Since the passivation occurs, the electromotive force of the local battery disappears and the corrosion stops, so the corrosion resistance could be significantly improved.

[Brief description of drawings]

FIG. 1 is an explanatory view showing a corrosion mechanism in a chromium plating film of the present invention.

FIG. 2 is an explanatory view showing a corrosion mechanism in a conventional chromium plating film.

FIG. 3 is a diagram showing the relationship between the phosphorus content of a nickel-phosphorus alloy coating and the corrosion resistance and electrodeposition rate.

FIG. 4 is a diagram showing a relationship between a film thickness of a nickel-phosphorus alloy film and corrosion resistance and appearance.

 ─────────────────────────────────────────────────── --- Continuation of the front page (72) Inventor Akito Tsuchida 1487 Nagasawa, Yokosuka City, Kanagawa Prefecture (72) Inventor Shigeru Suzuki 2-19 Futabacho, Yokosuka City, Kanagawa Prefecture

Claims (2)

[Claims] 1. A nickel-phosphorus alloy containing 8 to 15% by weight of phosphorus is plated as a base layer for 5 to 20 μm,
Corrosion-resistant chrome plating characterized by being plated with chrome. 2. The corrosion resistant chromium plating according to claim 1, wherein a semi-bright nickel plating and a bright nickel plating are sequentially formed as a lower layer of the nickel-phosphorus plating.