NL9000308A - MIXTURE AND METHOD FOR MANUFACTURING METAL DEPOSITS. - Google Patents

Description

Title: Mixture and method of manufacturing metal deposits. DESCRIPTION

This invention concerns the electroless production of black nickel deposits.

Electroless deposition of nickel has been known for some time.

Electroless nickel plated articles are described e.g. in US-A-3,088,846. Today, there is a general commercial need, partly motivated by fashion issues, for black electroless nickel deposits primarily but not exclusively for decorative application. Such deposits are typically required on exposed metal parts and / or housings for television sets, video cassette recorders and hi-fi equipment.

EP-A-0.094.127 proposes a solution to the problem of manufacturing black electroless nickel deposits. It describes that an electroless nickel-coated article can be treated in a chromate ion, phosphate ion and optionally sulfate ion bath, and subjected to a periodic reversal flow. EP-A-0.094.127 indicates that the electroless nickel can be deposited from a bath marketed by Enthone under the trademark ENPLATE 415. (The word "ENPLATE" is a trademark.)

It has been found, however, that deposits formed by the ENPLATE 415 bath, which are then converted, only yield a quite black layer when the electroless metal deposition bath is older than 1, but not more than 3, metal turnovers. (A metal turnover is achieved when deposited from a metal deposition bath that weight of metal ions that was originally present in the bath; during the metal deposition, the bath is replenished with metal ions and generally with reducing agent.)

Since the electroless metal deposition bath can only be effectively used for two metal turnovers, neither of which is the first, if the nickel deposited subsequently turns black, a significant waste of materials of the metal deposition bath occurs unless this bath is used for other purposes during the first and after the third turnover.

It has now been found that the presence of saccharin in an electroless nickel plating bath provides the opportunity to deposit nickel throughout the life of the bath and that the deposited nickel-phosphorus alloy can then be blackened uniformly or at least in a better manner than it has been was possible.

According to a first aspect of the present invention, an electroless nickel deposition material containing saccharin with is provided. Saccharin is generally present in an effective amount to black the deposited nickel later.

It is to be understood that references made to "nickel deposition" in this specification include references to a deposited alloy of nickel and some other element, such as phosphorus, as typically formed in electroless nickel plating.

The nickel source can be nickel sulfate or another suitable soluble nickel salt. The amount of nickel present in the bath can be 0.1 - 50 g / l, e.g. 1-25 g / 1, typically 2 - 10 g / 1. In electroless metal deposition baths, the metal ion is not reduced by electricity, but by a chemical reducing agent. Any suitable nickel ion reducing agent can be used in the bath, but in practice the preferred reducing agent is likely to be sodium hypophosphite leading to a nickel phosphorus deposit. The reducing agent may be present in the electroless metal deposition material in an amount of 1 - 100 g / l, e.g. 5 - 50 g / 1, typically 20 - 40 g / 1.

In order to avoid premature reduction of the nickel ions in mass solution, it is customary for an electroless nickel plating material to include a complexing agent with nickel ions. Any suitable complexing agent can be used, but lactic acid is a preferred complexing agent. (It will be understood that references in this specification to lactic acid or other weak organic acid include references to lactate or other corresponding ions as it will, of course, depend on the pH which species is present.) Other complexing agents which, in addition to lactic acid useful may include succinic acid, glycolic acid, malic acid and citric acid. The complexing agent can be present in an amount of 1 - 100 g / l, e.g. 5 - 50 g / 1 and typically 20 - 40 g / 1. Other complexing agents, including mixtures, can be used.

Saccharin is generally present or added to the bath in soluble form. A suitable soluble form of saccharin is sodium saccharin, but other soluble salts can be used. The saccharin should be present in the bath in an amount of at least 0.7 g / l for good results. Furthermore, if more than 2 g / l is present, it has been found that this can sometimes give rise to a mottled effect after blacking. Between 1.0 and 1.8 g / l, e.g. 1.5 g / l was found to be a particularly suitable amount of saccharin. As a further guideline, it has been found experimentally that for the maintenance of the bath the addition of between 25 and 200 mg saccharin per gram of nickel consumed has been found to give good results; preferred ratios are between 75 and 125 mg of saccharin per gram of nickel, with the addition of about 100 mg of saccharin per gram of nickel proving to be optimal.

A buffer may be present in the bath. The buffer can be an acetic acid / acetate system, although any other buffer, e.g. based on a weak organic acid and its salt, can be used. The buffer can be present in an amount of 1-50 g / l, e.g. 5-40 g / 1, typically 20 - 30 g / 1. If sodium acetate is used as a buffer, it can be supplied as the trihydrate salt.

The mixture may additionally contain one or more stabilizers. In appropriate amounts, lead has been found to be a suitable stabilizer for electroless nickel systems. Lead can be added as lead acetate or as any other suitable soluble lead salt. Lead can be present in an amount of 0.1-5 mg / l, e.g. 0.2-3 mg / 1, typically 0.5-1.5 mg / 1.

Sulfur-containing compounds are a further class of useful stabilizers. A useful compound of this class is 3 - ((amino-iminomethyl) thio) -1-propanesulfonic acid, although others can be used. The sulfur-containing compound can be present in an amount of 0.1-10 mg / l, e.g. 0.2-5 mg / 1, typically 0.5-3 mg / 1.

The pH of the electroless nickel plating mixture is usually on the acidic side. The pH can be 3-6, e.g. 4 - 5.5, typically 4.5 - 5.

According to a second aspect of the invention there is provided a process for the production of a black electroless nickel deposit, the process comprising: contacting a substrate for deposition with a saccharin-containing electroless nickel plating mixture, and forming a conversion layer containing chromium. The conversion layer may contain phosphorus and optionally sulfur. In particular, the conversion layer may contain a hydrated, basic chromium phosphate, which may contain the components CrPO ^ and Cr (OH) where Cr ^ (SO ^) ^ may be present and the weight ratio Cr: P: S = 1: (0 , 2 to 1.5): (0 to 0.5).

In the formation of the electroless nickel deposition, the temperature of the metal deposition mixture may be from 40 to 99 ° C, e.g. 60 - 95 ° C, typically 85 - 9> C. Metal deposition can take place for a suitable period of time, e.g., 5 minutes to 5 hours, depending on the thickness required. Deposition periods of 20 minutes to 2 hours are common, while periods of 30-45 minutes are typical of obtaining a thickness of about 10 µm of the deposition.

The conversion layer can contain chromium, phosphorus and sulfur, the ratio Cr: P: S = 1: 1: (0 - 0.2).

The conversion layer is generally formed on an electroless nickel-plated article treated with periodic reversing current, as described in EP-A-0 094 127, which. to the extent permitted by law, this reference should be deemed to be inserted. The frequency of the current reversal can be 0.1 - 50 Hz, e.g. 0.5 - 25 Hz, typically approx. 1 Hz, amounts,

The ratio of the time during which the electroless nickel-plated article is the cathode and the duration during which it is the anode at a given current cycle (t / t) need not be equal to cdx an of 1. A t / t ratio of 0.05-20 can generally be canned.

suitable, but a t / t ratio of less than 1 is preferred.

C & t 3.Π t, / t ratios of 0.1 to 0.8 were found to be most acceptable.

The current density can typically be 0.1 - 1 ASD, e.g. 0.2 - 0.5 ASD, typically about 0.25 ASD.

According to an important preferred feature of the invention, it has been found that if nitrate ions are present in the conversion mixture, the performance is improved: improvements in throwing power were observed and the tendency to form greenish colors in areas of high current density was markedly reduced. Therefore, the conversion mixture preferably contains nitrate ions, which can be added as nitric acid. 1-10 ml / l nitric acid (65%) was found to be suitable, e.g. 5-10 ml / 1, with about 7.5 ml / 1 being optimal.

The chromate ions in the conversion mixture can be present in an amount of 1 - 40 g / l CrO 2, e.g. 2 - 20 g / 1, typically 5 - 15 g / 1. Phosphate ions can be present in an amount that would be provided by the addition of 1-60 ml / l concentrated phosphoric acid, e.g. 2-40 ml / 1, typically 10 - 30 ml / 1. Sulfate ions can be present in an amount provided by 0-10 ml / l concentrated sulfuric acid, e.g. 0.1-5 ml / 1, typically 0.5-3 ml / 1.

Other preferred properties of the conversion mixture and the conversion process can be found in EP-A-0.094.127.

The invention is now illustrated by the following examples. Example 1

An electroless nickel plating mixture was prepared in water as follows:

Ni2 + (as nickel sulfate) 6.2 g / 1 lactic acid (80% w / v) 30.0 ml / 1 CH ^ COONa.3Η ^ Ο 24.0 g / 1

Na hypophosphite 30.0 g / 1 2+

Pb (as lead acetate) 1.3 mg / 1 3 - ((amino-iminomethyl) thio) -1-propanesulfonic acid 2.0 mg / 1

NaOH, about 3.6 g / l

Na-saccharin 1.5 g / 1 pH 4.8 *

A steel sheet was provided with a deposited metal layer in the above mixture for 35 minutes at pH 4.9 and a temperature of 89 ° C.

Example 2

The nickel-plated steel sheet obtained according to example 1 was treated in a solution with the following composition:

CrO 3 10 g / 1 H3PO4 (85%) 20 ml / 1 H 2 SO 4 (98%) 2 ml / 1 under conditions under which the flow was periodically reversed, as generally described in EP-A-0 094 127, but using the following specific parameters: anodic time 0.8 seconds cathodic time 0.2 seconds

current density 0.25 ASD

temperature 20-22 ° C

The electrolytic treatment lasted 30 minutes. Excellent uniform black deposit was obtained.

Example 3

Steel plates were nickel plated as described in Example 1. During nickel plating, nickel was added along with. appropriate additional amounts of hypophosphite and stabilizer to return the ingredients to their original concentrations. Furthermore, lactic acid was added to prevent precipitation of nickel orthophosphite, which is an unavoidable by-product of the process. After 1, 2, 3, 4 and 5 metal turnovers, a steel sheet was subjected to the conversion process described in Example 2. In any case, an excellent uniform black deposit was obtained.

Comparative example

A steel sheet was electroless coated with nickel in a composition as described in Example 1, except that the sodium saccharin was omitted. After one metal turnover, the steel panel was taken from the bath and subjected to the conversion process described in Example 2. Areas of the converted nickel deposit having a high current density were dark green, areas of medium current density were black with some iridescence, and areas of low current density were iridescent and dark; a satisfactory black deposit was not obtained.

Claims (22)

1. Electroless nickel plating mixture containing saccharin. The mixture of claim 1, wherein nickel is present in an amount from 1 to about 25 g / l. Mixture according to claim 1 or 2, containing a reducing agent present in an amount of about 5 to about 50 g / l. The mixture of claim 3, wherein the reducing agent comprises sodium hypophosphite. Mixture according to claim 1 or 2, containing an agent which forms a complex with the nickel ion in an amount of about 5 to about 50 g / l. The mixture of claim 5, wherein the complexing agent. lactic acid. The mixture of claim 1, wherein the saccharin is present in an amount of at least about 0.7 g / l. The mixture of claim 1, wherein the saccharin is present in an amount up to about 2 g / l. A mixture according to claim 1, containing from about 5 to about 40 g / l buffer. The mixture of claim 9, wherein the buffer comprises acetic acid. Mixture according to claim 1, containing one or more stabilizers. A process for the preparation of a black electroless nickel deposit, the process comprising: contacting a substrate for this deposition with a saccharin-containing mixture for electroless nickel plating, and forming a conversion layer comprising chromium. The method of claim 12, wherein the conversion layer comprises phosphorus and optionally sulfur. The method of claim 13, wherein the conversion layer comprises a hydrated, basic chromium phosphate, which comprises the components CrPO2 and (Cr (OH) 3), wherein Cr2 SO2) can be present, and wherein the weight ratio Cr: P: S = 1: (0.2 - 1.5): (0 - 0.5). The method of claim 12, wherein the conversion layer is formed by treatment in a periodic reverse flow conversion mixture. The method of claim 15, wherein the frequency of the current reversal is about 0.5 to about 25 Hz. The method of claim 12, wherein the ratio of the time during which the electroless nickel-plated article is the cathode and the time during which it is the anode at a given current cycle (t Vt) is about 0.1 to about 0.8 is cat an The method of claim 12, wherein the conversion layer is formed by contacting a conversion mixture containing nitrate ions. The method of claim 18, wherein nitrate ions are present in an amount as supplied by about 5 to about 10 ml / l nitric acid (65%). 20. A method according to claim 12, wherein conversion is effected by contact with a mixture containing about 2 to about 20 g / l CrO 2. The method of claim 12, wherein conversion is by contact with a mixture containing phosphate ions in an amount such as is provided by about 2 to about 40 ml / l concentrated phosphoric acid. The method of claim 12, wherein conversion is by contact with a solution containing sulfate ions in an amount such as is provided by about 0.1 to about 5 ml / l concentrated sulfuric acid.