NO810448L - GLASS FOR SINK ELECTROPLETTING SOLUTIONS - Google Patents

Description

The present invention generally relates to aqueous, acidic or alkaline zinc electroplating solutions and a method for using such solutions for depositing a corrosion-resistant and decorative zinc electroplating coating on a number of substrates such as e.g. ferrous objects such as iron and steel. A number of such zinc electroplating solutions have previously been proposed for commercial use and used containing various additives to increase gloss, ductility, adhesion and/or leveling of the electrocoating. Conventionally, such additives are used in a mixture whereby each of a number of gloss agents contributes to the desired end result.

The present invention provides an improved aqueous zinc electroplating solution which overcomes some of the problems and shortcomings in connection with previously known formulations and contains a primary gloss agent which provides a shiny, ductile and adherent zinc coating and which can be used both in acidic chloride and sulfate type solutions as well as in cyanide and non-cyanide zinc electroplating solutions of the alkaline type. The improved aqueous zinc electroplating bath is suitable for use over a wide pH range as well as over a wide range of current densities.

The advantages of the invention are achieved by an aqueous zinc electroplating solution containing zinc oxides and an effective amount sufficient to provide a glossy, adherent and ductile zinc coating on a conductive substrate of a bath-soluble brightening agent and mixtures of brightening agents represented by the structural formula:

in which:

R is H or C 8 -C 10 aryl, or C 6 -C 20 alkylaryl wherein the alkyl group is C -C -C ; or C^-C22~<a>lky1 or ^ 2~ C10 neterocyclic nitrogen compound having at least one tertiary or quaternary ring containing nitrogen; as well as mono-, di- or tri-substituted derivatives thereof including -OH,

-SO₂H or -COOH; group I and group II as well as NH^ salts thereof; and aldehyde, ketone and ether derivatives thereof;

X is R or -OR' or -NR^ wherein R' is H or

a C-j^-C^ aliphatic residue; and

Y is H or SO 3 H

as well as compatible bath-soluble salts thereof.

The bath-soluble salts of the brighteners usually include Group IA and Group IIA metals as well as ammonium aq.

The primary gloss agent can be used in amounts of approx. 0.001 up to approx. 10 g/l as amounts of approx. 0.01 - approx. 5 g/l is preferred. In addition to the primary brightener, the electroplating solution may further contain one or more supplemental or secondary brighteners of various types well known in the art and suitable for use in this particular acid chloride, acid sulfate or alkaline zinc plating solution.

According to the method according to the invention, glossy, ductile and adherent zinc electroplating coatings are deposited on conductive substrates using the above-mentioned aqueous zinc electroplating solutions which are regulated to a temperature of approx. 15 and until approx. 82°C at current densities within the range 1 up to 300 amperes per square feet depending on the particular type and composition of the electroplating solution.

Further, advantages of the invention will be apparent from the following description of preferred embodiments in connection with the accompanying examples.

The improved aqueous zinc electroplating solution according to the invention contains as primary gloss-giving compound a compound with the structural formula:

where in:

R is H or C 8 -C 20 -aryl or C 8 -C 20 -alkylaryl wherein the alkyl group is C1-C4' or C1-C22 alkyl or C1-C2 heterocyclic nitrogen compound with at least one tertiary or quaternary ring containing nitrogen; as well as mono-, di-, or trisubstituted derivatives thereof including -OH, -SO^H or -COOH; group I and group II as well as NH^ salts thereof; and aldehyde, ketone and ether derivatives thereof;

X is R or -OR' or -NR^ wherein R' is H or

a C-^-C^j aliphatic residue; and

Y is H or SO 3 H

as well as compatible bath-soluble salts thereof.

Characteristic compounds that can be used as primary gloss-giving agents according to the structural formula stated above are those listed in table 1.

Table 1

3- sulfopropanoic sodium salt,

4-phenyl-4-sulfobutan-2-one sodium salt,

4-phenyl-4-sulfobuten-2-one sodium sulfate,

4-phenyl1-4,4-disulfobutan-2-one disodium salt,

4-sulfo-4-(3,4-dimethoxyphenyl)-butan-2-one sodium salt, 4-(3,4-methylenedioxyphenyl)-4-sulfobutan-2-one sodium salt, 3-sulfo-3-phenylpropanal- sodium salt,

3-sulfo-3-phenylpropanoic acid monosodium salt,

1,3-diphenyl-3-sulfopropan-1-one sodium salt,

3-sulfobutanal sodium salt,

3-(2-furyl)-3-sulfopropanal sodium salt,

3-(3-Indolyl)-3-sulfopropanoic acid monosodium salt, 3-(5-bicyclo-[2.2.1]-heptene)-3-sulfopropanoic acid monosodium salt,

4-sulfobutan-2-one sodium salt,

3.3-diphenyl-3-sylphopropenal sodium salt,

3-phenyl-3,3-disulfopropanal disodium salt,

1-(4-piperidyl)-3-sulfo-5-(3,4-methylenedioxyphenyl)-4-penten-1-one sodium salt,

1-(4-piperidyl)-5-sulfo-5-(3,4-methylenedioxyphenyl)-2-pentene-. 1-on sodium salt,

1-(4-piperidyl)-3,5-disulfo-5-(3,4-methylenedioxyphenyl)-1-pentanone disodium salt,

3-(3-Pyridyl)-3-sulfopropanoic acid monosodium salt, 3-(4-Imidazyl)-3-sulfopropanoic acid monosodium salt, 4-pheny1-2-sulfo-4-oxobutanoic acid monosodium salt, 4-phenyl-3-sulfo- 4-oxobutanoic acid monosodium salt, 1,7-di-(3-methoxy-4-hydroxyphenyl)-7-sulfo-1-heptene-3,5-dione disodium salt,

1,7-di-(3-methoxy-4-hydroxyphenyl)-1,7-disulfohepta-3,5-dione disodium salt,

4-(2-furyl)-4-sulfobutan-2-one sodium salt,

4-pheny 1-4-sulf obutan-2-one sodium salt ,■

4-phenyl-4,4-disulfobutan-2-one disodium salt, 3-pheny1-3-sulfopropenal sodium salt,

3-phenyl-3,3-disulfopropanal disodium salt,

4- sulfobuten-2-one sodium salt,

4.4- Disulfobutan-2^one disodium salt.

The gloss-giving agents according to the invention can conveniently be prepared by reacting essentially equal molar amounts of an α,|3-unsaturated carboxyl compound with an alkali metal or ammonium bisulphite or -metabisulphite in an aqueous or aqueous organic solvent at temperatures up to reflux temperatures for a period of time sufficient to effect substantially complete reaction. The reaction product can be isolated by crystallization from the reaction mixture and can be further purified by recrystallization.

E.g. 4-phenyl-4-sulfobutan-2-one sodium salt can be prepared according to the following procedure: To a solution of 26.15 g or 0.25 mol of sodium metabisulphite in 50 ml of r^O heated to 45°C added 40.2 g or 0.275 mol of a liquefied benzalace ton. The solution was stirred and heated to reflux temperature, 105°C, at which point the reaction became exothermic. The heat was removed and the reflux continued alone for 5-10 minutes, after which the reaction mixture was clear and only one layer was visible. The reaction mixture was cooled slowly and a small amount of ether was added for extraction. Because the solution began to solidify, 175 ml of water was added and then the water content was reduced by volume slowly until crystallization just began. Recrystallization from acetone and drying in a vacuum desiccator heated to 70°C gave 45 g of 4-phenyl-4-sulfobutan-2-one sodium salt in a yield of 73%.

According to the invention as far as the composition is concerned, the primary brightening agent as indicated in table 1 or mixtures thereof can be used in aqueous zinc electroplating solutions in regulated effective quantities to provide a shiny, ductile and adherent zinc coating. In general, the amount is within the range of 0.001 and up to 10 g/l, while amounts of approx. 0.01 up to approx. 5 g/l is usually preferred.

The primary brighteners can be used in aqueous acidic zinc chloride electroplating solutions, aqueous acidic zinc sulfate electroplating solutions as well as in aqueous alkaline cyanide and non-cyanide zinc electroplating solutions. The primary brightening agent is particularly applicable in solutions of the non-cyanide type. The concentration of the zinc ions in such solutions can generally range from approx. 5 g/l and up to saturation in the solution at the particular operating temperature for the bath, e.g. 300 g/l or higher at bath temperatures of approx. 38°C and above. Characteristically, in acidic chloride solutions the zinc ion concentration is conventionally controlled to within a range from approx.

7 - approx. 50 g/l. In acid sulfate electroplating solutions, the zinc ion concentration is usually regulated to within a range of approx. 30 to up to 110 g/l while the zinc ion concentration in aqueous alkaline non-cyanide zinc solutions is usually regulated to within a range from approx. 5 and up to 25 g/l. It will be clear from the foregoing that the zinc ion co-concentration for the various non-cyanide electroplating solutions can generally be used in an amount within the range of approx. 5 and up to saturation, and preferably from approx.

5 g/l to approx. 110 g/l.

In acidic chloride electroplating solutions, it is conventional to further incorporate inert salts to increase the conductivity of the solution and these are usually used in amounts from approx. 20 and up to approx. 450 g/l. Such inert salts appropriately include alkali metal chlorides in which the term "alkali metal" is used in its most comprehensive sense to also include ammonium chloride as well as specific alkali metals such as sodium, potassium and lithium.

It is also conventional practice to use suitable buffering agents in acid chloride and acid sulfate electroplating solutions. Characteristically, boric acid can be used for this purpose and used in quantities within the range of approx. 1 and up to approx. 40 g/l. In acidic plating baths, the pH value can be within the range 1.0 - approx. 6.5. In the acidic chloride electroplating solution, the hydrogen ion concentration is usually regulated so that an operating pH value for the bath of approx. 4.5 and up to approx. 6.2, while the hydrogen ion concentration in acidic sulphate electroplating solutions is usually regulated to a pH value of approx. 3.5 and up to 5.2.

In alkaline cyanide and non-cyanide baths, the pH value is above approx. 8.0. In non-cyanide baths, suitable alkali metal hydroxides such as sodium hydroxide or potassium hydroxide are used to provide conductivity to the bath and to further provide a hydroxyl ion concentration to achieve an operating pH value in the bath which is usually above approx. 12.

In addition to zinc ions and primary brightening agent, the aqueous zinc electroplating solutions may further contain supplementary or secondary brightening agents of the type usually used in acid chloride, acid sulfate or alkaline cyanide or non-cyanide zinc electroplating solutions. Such additional glossing agents may be of any type known in the art and are generally used in amounts of up to about 10 g/l while amounts of approx. 0.2 and up to approx. 5 g/l is usually preferred. Characteristic of such secondary or supporting gloss-giving agents which can suitably be used in acidic zinc chloride electroplating solutions are polyethers, aromatic carboxylic acids and their salts, nicotinate quaternary compounds and the like. For alkaline zinc electroplating solutions, additional brightening agents of the type comprising polyamine and polyethyleneimine quaternary compounds, aromatic aldehydes, polyvinyl alcohols and the like are typical. For acidic zinc sulfate electroplating solutions, characteristic additional glossing agents are polyacrylamides. thioureas, nicotinate-quaternary compounds, etc. Such additional gloss-giving agents are usually used in the form of a mixture of two or more in combination with the primary gloss-giving agent in the improved zinc plating bath according to the invention.

According to the method of the invention, one can work with the aqueous zinc electroplating solutions containing primarily a gloss-giving agent at approx. room temperature and up to approx. 50°C while temperatures within the range approx. 18°C and up to approx. 32°C is more characteristic. The current density at which the solutions can be used varies depending on the particular type of bath. E.g. alkaline zinc and acidic chloride electroplating solutions can be used at current densities of approx. 1 and up to 80 amperes per square feet while acid sulphate baths can be used at current densities of approx. 20 and up to approx. 300 amperes per square feet. The specific current density used will vary depending on the plating technique used, the type of object being plated and the particular bath composition and concentration.

To further illustrate the improved aqueous zinc plating solution of the invention, reference is made to the accompanying specific examples. It will be clear that the examples are only illustrative and are not intended to be restrictive of the invention as described herein and as described in the accompanying claims.

Example I

An acidic chloride zinc electroplating solution is prepared containing 30 g/l zinc ions, a total chloride ion content of approx. 300 g/l, boric acid in an amount of approx.. 2 7 g/l, 0.5 g/l of a carrier or an additional brightening agent comprising the commercially available compound "Surfynol 485" (acetylenic glycol 2,3.7.9 -tetramethyl-5-decyn-4,7-diolethoxylated) and 0.3 g/l primary brightening agent, 3-sulfopropanal sodium salt. According to the structural formula given above, this corresponds to primary gloss. agent a compound in which R is H, X is H and Y is H.

Objects plated in this solution at a cathodic current density of approx. 40 amperes per square feet gave

good overall shine in the ductile and adherent zinc coating.

Example II

An acidic chloride zinc electroplating solution is prepared containing 25 g/l of zinc ions, a total chloride ion content of 280 g/l, 27 g/l of boric acid, 3 g/l of benzoic acid as an additional brightening agent, 0.4 g/l of the additional brightening agent agent "Surfynol 485" as used in example I and as primary gloss agent 4-phenyl-4-sulfobutan-2-one sodium salt in a concentration of 0.05 g/l. This primary gloss corresponds to the above structural formula where R is a phenyl group, X is a methyl group and Y is H.

Articles coated in this bath solution at a cathodic current density of 50 amperes per square foot gave good overall gloss for the ductile and adherent zinc coating.

Example III

An acid chloride zinc electroplating solution is prepared containing 35 g/l zinc ions, 320 g/l chloride ions in total, 27 g/l boric acid, 2 g/l salicylic acid as additional gloss agent, 0.25 g/l ethoxylated 3-naphthol as additional gloss agent agent and 0.06 g/l 3-sulfo-3-phenylpropanal sodium salt as primary gloss agent. The bath has a pH of approx. 5.5.

The primary brightening agent corresponds to the above structural formula in which R is phenyl, X and Y are equal to H.

Articles coated in this solution at a cathode current density of 30 amperes per square foot gave good overall gloss in the adherent and ductile zinc coating.

Example IV

An alkaline solution was prepared containing 8 g/l zinc ions, 80 g/l sodium hydroxide, 1 g/l polyethyleneimine quaternary compound as an additional brightening agent and 0.5 g/l 4-sulfo-4-(3,4-dimethoxyphenyl) )-butan-2-one sodium salt as primary gloss agent. This agent corresponded to a structural formula where R comprises a substituted phenyl group with 2 ether groups, X is a methyl group and Y is H.

The pH value of the bath was 14. A "Hull Cell" plate coated in this solution at a current density of 1 amp gave a good shine at current densities below approx. 50 - 60 amperes per square feet.

Example V

An acidic sulphate plating solution is prepared containing 180 g/l zinc sulphate monohydrate, 30 g/l boric acid, 15 g/l ammonium sulphate and 0.5 g/1 4-phenyl-4-sulfobutan-2-one sodium salt as the primary brightening agent. The solution had a pH value of approx. 4.2.

Sample plates coated in this solution at a current density of approx. 20 - approx. 90 amperes per square feet gave very good semi-gloss zinc coatings.

Example VI

An acidic chloride plating solution is prepared containing 35 g/l zinc ions, 2l0 g/l chloride ions together, 1 g/l ethoxylated α-naphthol as an additional brightening agent,

as well as 0.5 g/l 3-sulfo-3-phenyl-propanoic acid monosodium salt as primary gloss agent. This primary remedy corresponds to

the above formula wherein X is OH, R is phenyl and Y

is H. The pH of the solution is approx. 5.0.

Objects coated with this solution at a cathode current density of approx. 40 amperes' per square feet gave good overall, gloss.

Example VII

An acid chloride plating solution is prepared containing 30 g/l zinc ions, 260 g/l total chloride ions, 30 g/l boric acid, 0.75 g/l "Surfynol 485" as an additional brightening agent and 0.05 g/l 4-phenyl -4-sulfobuten-2-one sodium salt.

Sample plates coated with this solution at a temperature of approx. 24°C in the presence of air agitation at a pH

of 5.3 and a current density of 35 amperes per square feet provided substantially uniform gloss over the entire surface area.

Example VIII

An acid chloride electroplating solution is prepared containing 35 g/l zinc ions, 300 g/l total chloride ions, 20 g/l boric acid, 0.5 g/l "Surfynol 485" as additional brightening agent, 0.025 g/l 4-phenyl-2 -butyn-2-one as second additional brightening agent and 0.03 g/l of a mixture of 4-phenyl-4-sulfobuten-2-one sodium salt and 4-phenyl-4-disulfobutan-2-one sodium salt. The solution had a pH value of approx. 5.5.

Test plates coated with this solution at a current density of approx. 45 amperes per square feet under air stirring and a bath temperature of approx. 24°C gave very good and clear color and gloss.

It will be clear that the examples illustrate advantages of the invention, it should also be clear that they are not intended to be limiting.

Claims (11)

1. Aqueous zinc electroplating solution comprising zinc ions and an effective amount sufficient to provide a shiny, adherent and ductile zinc coating on a conductive substrate, of a bath-soluble polishing agent, characterized in that the polishing agent is a compound or mixtures of compounds represented by the structural formulas : in which: R is H or C 8 -C 4 -aryl, or C 8 -C 4 -alkylaryl wherein the alkyl group is C-^ -C^ ; or C-1-C1-alkyl or C2-C10 heterocyclic nitrogen compound having at least one tertiary or quaternary ring containing nitrogen; as well as mono-, di- or tri-substituted derivatives thereof including -OH, -SO₂ H or -COOH; group I and group II as well as NH^ salts thereof; and aldehyde, ketone and ether derivatives thereof; X is R or -OR' or -NR^ wherein R' is H or a C 1 - C 4 aliphatic residue; and Y is H or SO 3 H as well as compatible bath-soluble salts thereof. 2. Plating solution according to claim 1, characterized in that the gloss-giving agent is present in an amount of approx. 0.001 - approx. 10 and preferably from approx. 0.01 - approx. 5 g/l. 3. Solution according to claim 1, characterized in that the zinc ions are present in an amount of from approx. 5 - approx. 110 g/l. 4. Solution according to claim 1, characterized in that it comprises an acidic chloride solution containing zinc ions in an amount from approx. 7 - approx. 50 g/l and hydrogen ions to give a pH value between approx. 4.5 and approx. 6.2.. 5. Solution according to claim 1, characterized in that it comprises an acidic sulfate solution containing zinc ions in an amount of approx. 30 - approx. 110 g/l and hydrogen ions to give a pH value of approx. 3.5 - approx. 5.2. 6. Solution according to claim 4 or 5, characterized in that it further contains approx. 1 - approx. 40 g/l boric acid as a buffer. 7. Solution according to claim 4, grade i-, characterized in that it further contains approx. 20 - approx. 450 g/l alkali metal chloride salts. 8. Solution according to claim 1, characterized in that it comprises an aqueous solution containing zinc ions in an amount of approx. 5 - approx. 25 g/l and an alkali metal hydroxide to give a pH value of approx. 12 - approx. 14. 9. Solution according to claim 1, characterized in that it further contains compatible secondary gloss-giving agents in an amount of up to 10 g/l, preferably approx. 0.2 - approx. 5 g/l. 10. Method for electrodeposition of zinc on a substrate, characterized in that it comprises electrodeposition of zinc from an aqueous zinc electroplating solution as stated in any one of claims 1-5 or 7-9. 11. Method for electrodeposition of zinc on a substrate comprising electrodeposition of zinc from an aqueous zinc electroplating solution as set forth in claim 6.