JPH0660432B2 - Plating method for avoiding dark deposition when depositing a matte coating from a bright nickel bath or a bright nickel / cobalt alloy bath - Google Patents

Description

TECHNICAL FIELD The present invention contains an organic brightener and a nonionic surfactant,
The nonionic surfactant is present as an emulsified second phase at bath treatment temperatures. The present invention relates to a technique for depositing a matte coating, a so-called velvet-like coating, on a surface of a conductive substrate from an iron-free bright nickel electroplating bath or a bright nickel / cobalt alloy electroplating bath. More specifically, the invention relates to means for avoiding dark deposits and / or black pores that occur during the deposition of this coating.
This matte coating is characterized as a matte coating or a velvety-like coating or a shusu-like coating.

In the following, the term bright nickel is meant to include bright nickel / cobalt alloys as well, but the following points should be noted in relation to the above technology. That is, the matte bright nickel layer has been used for a long time in durable tools such as sanitary equipment, furniture decoration fittings, and household appliances due to its special decorative effect. The bright nickel electroplating bath additionally contains foreign substances, either inorganic or organic, which either accumulate in the bright nickel layer or impede nickel deposition by electrostatic distribution in the cathodic coating. In either case, the surface of the coating is damaged and the incident light is diffusely reflected.
Therefore, this foreign substance in the bath should be as finely and uniformly dispersed as possible, or emulsified, to give a matte effect, i.e. a glint-free or low-gloss effect, over the entire surface of the substrate.

To this end, it is more finely dispersed or emulsified than dispersed inorganic materials such as oxides, carbides, diamond powders, etc. which are industrially customarily used to provide wear resistant dispersed nickel coatings. Organic foreign substances are preferred. The above-mentioned inorganic substances also have the drawback of high density. This is significantly affected by gravity, which gives the deposited coating a different degree of matting. Matte bright nickel coatings as used herein should not be confused with plain nickel coatings which are deposited without brightener from, for example, Watt's nickel electrolyte.

In the bath forming the basis of the present invention (West German Patent No. 1621087), the bath for depositing the matte bright nickel coating contains a nonionic surfactant, which precipitates with increasing temperature and is electrolyzed as an organic foreign substance. Form a liquid and an emulsion. This emulsion leads to agglomeration which must be avoided. Special measures are needed to bring the method to practical use. The bath must be cooled in the associated circulation, thereby bringing it below the cloud point of the nonionic surfactant and re-dissolving it in the bath. The bath must then be heated again to the required processing temperature, which again leads to emulsification. Therefore, special heating / cooling-attached circulation is required. The known baths contain organic brighteners containing aromatic sulfonic acids and sulfonamides and sulfonimides because of the matte bright nickel layer. This has the drawback of giving a milky dark deposit with black pinholes in the low cathode current density area. On the other hand, on the other hand, it is often necessary to treat with a low average current density in the range of 0.5 to 5 A / dm ² , and in the case of substrates with extremely complex contours, such as instruments, a low cathode current density is unavoidable. Is. Moreover, when using known baths, the above disadvantages cannot be avoided by increasing the average cathode current density. This increase in current density locally causes so-called charring, that is, coarse crystalline or amorphous deposition on the exposed surface portion. Especially when a coating layer, in particular a metal carbide and / or metal nitride coating layer, is formed on the surface of the coating, the black pinholes are particularly disturbing. At this time, this black pinhole exudes, so to speak.

In order to avoid the above-mentioned drawbacks, it is proposed to treat using a special foreign substance (West German Patent 2327881).
issue). However, in the known measures so far,
Organic foreign substances in the electrolyte are formed by the reaction of at least one cationically active or acid / alkali amphoteric substance with the organic anion of at least one compound. The anion-donating substances are, in particular, alkyl- or arylsulfates, alkyl- or arylsulphonic acids and sulfinic acids, as well as sulfonamides or sulfonimides. The electrolytic solution further contains known primary and / or secondary brighteners in order to provide a matte and glossy character. This organic foreign substance provides a decoratively effective matting within a certain treatment time, after which the foreign substance must be filtered off as a result of the agglomeration phenomenon. Therefore, organic foreign substances have to be added again each time for the next treatment cycle, which leads to high costs.

Therefore, the technical problem in this field to be solved by the present invention is the bath mentioned at the beginning of the specification, especially West German Patent 162.
Suppressing the occurrence of dark deposits and / or black pinholes when depositing a matte coating on the surface of a conductive substrate from No. 1087 bath.

SUMMARY OF THE INVENTION This technical problem, however, is based on the fact that iron-free, containing organic brighteners and nonionic surfactants, the nonionic surfactants being present as an emulsified second phase at bath treatment temperatures. A plating method for avoiding dark color deposition and / or formation of black pinholes when depositing a matte coating on the surface of a conductive substrate from a bright nickel electroplating bath or a bright nickel / cobalt alloy electroplating bath. In addition to organic brighteners and nonionic surfactants, benzenesulfinic acid,
p-Toluenesulfinic acid or an alkali metal salt thereof is added alone or as a mixture in an amount of less than 100 mg / l so as not to impair the matting effect, and
Solution by a plating method characterized by being treated with an average cathodic current density in the range of 5 to 5 A / dm ² and by heating / cooling-attached circulation equipped with a filtration device, the two-phase state of the bath is sufficiently maintained. It has been found that this can be done.

The matte coating formed by such a plating method can have a coating layer formed thereon, especially a metal carbide and / or metal nitride coating layer deposited thereon. It is also possible to electroplate a bright chrome coating on the matte coating.

Adding organic sulfinic acid to a bath containing an emulsifying foreign substance for depositing a nickel- or nickel-alloy-containing schuss-like coating, and further stabilizing heating / cooling-emulsion so as not to require additional circulation. Is basically known (West German publication No. 3736171.6). However, it must be added in large quantities and not always achieve its purpose.

(Structure of the Invention) In the present invention, a conventional primary brightening agent (eg, sulfonimide, sulfonamide, benzenesulfonic acid, naphthalenesulfonic acid, alkanesulfonic acid, arylsulfonate) and a secondary gloss are used in the bath. In addition to agents (eg alkenes or alkyne sulfonic acids or alkali metal salts of sulfonic acids), benzenesulfinic acid and /
Alternatively, p-toluenesulfinic acid, especially its sodium salt, is added in an amount of less than 100 mg / l. When the concentration of the organic sulfinic acid or its salt is too high,
At the same cathodic current density, too much gloss is produced in the deposited film, which hinders the matte effect. The person skilled in the art can determine with a simple test in advance how much sulfinic acid is preferred in each case. In this case, the amount of sulfinic acid must be selected to be relatively small, and at the same time, it is necessary in principle that the concentration of the emulsifier in the bath be selected to be relatively small. In the present invention also alkylsulfinic acids such as methane, ethane, propane, butanesulfinic acid, dimethanedisulfinic acid,
Basically, dichloromethanesulfinic acid can also be used. However, this aliphatic sulfinic acid is often unstable in water.

According to the present invention, when a matte bright nickel layer or a bright nickel / cobalt alloy layer is deposited and deposited from an emulsion-containing nickel bath, especially a bath according to German Patent 1621087, dark color deposition in a low cathode current density range is effective. Can be blocked. This is based on the fact that, in the bath as described above, under its operating conditions, it is a two-phase system of the dissolved substance and the undissolved or emulsified substance. The cause of the dark deposits at low cathodic current densities lies in the insoluble organic matter, which on the other hand must be present in order to give a matting effect.
Although it has been known that sulfinic acid provides a high tolerance for dissolved impurities in electroplating baths, the ability to avoid and overcome the aforementioned drawbacks in two-phase systems containing insoluble materials is
This is something that could not be expected before the present invention. The invention can be used not only in pure nickel electrolytic baths such as the Watts bath consisting of nickel sulphate, nickel chloride and boric acid, but also in nickel / cobalt alloy electrolytic baths. In the latter case, an additional limited amount of cobalt sulfate or cobalt chloride is added to the Watts bath.
The previously mentioned heating / cooling circulation according to West German patent 1621087 must also be set up in this improved method according to the invention.

The present invention will be described more specifically by the following examples.
The present invention allows electrolytic as well as non-electrolytic coatings (eg bright chrome or titanium nitride) to be formed on high quality, glare-free bright nickel layers.

Experimental Example 1 The following nickel bath was prepared, and electroplating was performed using this.

Nickel sulfate _x7H 2 O 300 g of nickel chloride _x6H 2 O 50 g boric acid 40g benzoate sulfonimide sodium salt 1 g EO content 20 wt%, PO content 80% by weight, average molecular weight of about 2
500 propylene oxide / ethylene oxide block copolymer 0.012 mmol Water was added to the above to prepare a 1 liter bath.

pH value 4.2 to 4.4 (adjusted with sulfuric acid or nickel carbonate) Temperature 52 ° C. Cathode current density 3 A / dm ² Anode Electrolyte nickel substrate according to DIN 1702 Mild movement Treatment time 15 minutes “LPW-Taschenbuch, Fur, Galva Notechinique ", 1988 thirteenth edition, Vol. 1, 570, p. 62.
A brass plate having the outer shape shown in the figure was degreased and purified by a conventional electroplating technique, and then plated with matte bright nickel in the above electrolytic bath. Dark deposits with black pinholes were observed in the low current density areas at the corners.

Experimental Example 2 To the electrolytic bath of the above Experimental Example 1, 0.12 mmol of benzenesulfinic acid sodium salt was added before heating.
A precipitation experiment was conducted. A glossy surface having a glare-free surface effect was observed at the corners of the test metal plate, and no black pinhole was observed.

Experimental Example 3 After plating a metal plate with nickel in the same manner as in Experimental Examples 1 and 2,
Bright chrome plating or Ti in a conventional manner in electroplating technology
A hard coating layer was formed by N vapor deposition (PVD method). Experimental example 2
By using a nickel bath similar to, the test metal sheet gave a satisfactory coating layer even in its corners.

Experimental Example 4 Instead of 0.12 mmol of benzenesulfinic acid sodium salt in Experimental Example 2, a corresponding amount of p-toluenesulfinic acid sodium salt was used. Also in this case, similarly, a deposited film having a matte gloss corner portion without black pinholes was formed.

Experimental Example 5 An electrolytic bath similar to those of Experimental Examples 1, 2 to 4 was prepared without adding a block copolymer as an emulsion forming agent.
No black pinholes were observed in the corners of the test plate in this case either. The deposited film exhibited a gloss (rather than a high degree of glare) rather than a plain background gloss.

It was used with the addition of cobalt sulfate x7H ₂ O in 30 g / l in the electrolyte bath of Experimental Example 6 Experimental Example 1-5. The results were the same as described above.

Experimental Example 7 An apparatus system for performing heating / cooling circulation (about 1/3 bath volume / hour) in which the same treatment as in Experimental Example 2 was cooled to 18 to 20 ° C. before heating the bath treatment temperature again. The prepared bath was run every hour. Similarly, a uniform matte gloss effect was produced by the continuous operation of the attached circulation system. The corners of the test metal plate also maintained their glossy state without producing black pinholes.

Experimental Example 8 The bath of Experimental Example 7 was subjected to an hourly precipitation-deposition treatment without operating the heating / cooling circulation system. The gloss state was maintained without causing black pinholes in the corners of the test metal plate, but the gloss effect without glare became poor and unsightly due to aggregation of the emulsion over time.
The agglomeration without activation of the heating / cooling circulatory system was determined by observing the surface conditions and the resulting R ₂ values and by the principle of the three-angle reflectometer (DIN 67530). The glossiness of the deposit is increased accordingly.

Similar experiments were carried out on actually mounted parts, but when the parts were mounted so as to be perfect members after the surface treatment, the difference in the matte gloss effect was extremely remarkable. In other words, the aesthetic effect of the surface was excellent and unrivaled. That is, a uniform matte gloss effect is ensured by the heating / cooling circulation system to be provided according to the invention.

Experimental Example 9 In the electrolytic baths of Experimental Examples 1 and 2, the amount of benzenesulfinic acid sodium salt was increased to 3.6 mmol and added, and a deposition experiment was conducted. In this case, the corners of the test metal showed a black pinhole-free luster, but with increasing amount, the matte luster effect confirms the unfavorable luster of the coating even at moderate and high cathodic current densities.
This effect can be compensated to a certain extent by increasing the concentration of the propylene oxide / ethylene oxide block copolymer, but such a measure again promotes the flocculation of the emulsion, which leads to heating / cooling circulation. It must be further strengthened, and if this is done under the necessary processing conditions, it will result in a significant cost increase. In other words, it is advantageous to keep the emulsion liquid concentration low, and the benzenesulfinic acid sodium salt concentration can also be selected low.

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Klaus, Schulze-Berge, Federal Republic of Germany, 5630, Remscheid, Adolf-Westen-Strasse, 14 (56) Reference JP-A-49-130835 (JP, A) JP-A-51-140842 (JP, A) JP-A-52-48526 (JP, A) US Patent 3839165 (US, A)

Claims (3)

[Claims] 1. An iron-free bright nickel electroplating bath or brightener comprising an organic brightener and a nonionic surfactant, the nonionic surfactant being present as an emulsified second phase at bath treatment temperature. A plating method for avoiding the formation of a dark color deposit and / or a black pinhole when depositing a matte coating on the surface of a conductive substrate from a nickel / cobalt alloy electroplating bath. In addition to the surface-active agent, benzenesulfinic acid, p-toluenesulfinic acid or alkali metal salts thereof, alone or as a mixture, are used so as not to impair the matting effect.
added in an amount less than mg / l, 0.5-5 A / dm
A plating method, characterized in that the bath is maintained at an average cathode current density in the range of ² and the two-phase state of the bath is sufficiently maintained by heating / cooling-attached circulation equipped with a filtration device. 2. A plating method according to claim 1, wherein a coating layer, in particular a metal carbide deposited on the matte coating, and / or
Alternatively, a plating method is characterized in that a coating layer of metal nitride is formed. 3. The plating method according to claim 1, wherein a glossy chromium coating layer is formed on the matte coating by an electroplating method.