CS258358B1 - Lee-forming pH set for electrolytic deposition of zinc coatings up to 50 µm thick - Google Patents

Abstract

A brightening additive for electrolytic deposition of zinc coatings from weakly acidic galvanizing baths without or containing ammonium salts, based on aromatic ketones, sodium or potassium salts of organic acids, non-ionic surfactants prepared by ethylene oxidation of aliphatic alcohols, non-ionic surfactants prepared by copolymerization of ethylene oxide with propylene oxide and containing 4-dimethylaminoazobenzene, 4'-dimethylaminoazobenzene-3-sulfonic acid, 4'-dimethylaminoazobenzene-2-carboxylic acid, or 4'-hydroxyazobenzene-4-sulfonic acid, which convert the decomposition products of aromatic ketones formed by the passage of electric current during galvanic plating into a very harmless form. They thus ensure long-term stability of coating parameters and significantly extend the interval after which the bath must be cleaned with oxidizing agents and activated carbon.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a gloss-forming additive for the electrolytic deposition of glossy zinc coatings from weakly acidic zinc baths containing ammonium salts consisting of or containing zinc chloride or ammonium chloride or ammonium salts consisting of zinc chloride or sulfate, sodium or potassium chloride and boric acid. .

A number of organic substances have been proposed for the deposition of zinc coatings from weakly acidic baths, which influence the course of electrocrystallization and provide suitable coating parameters. The mechanism of their action is the sorption at the active centers of the parent metal crystal lattice, which causes an increase in the number of crystallization centers. The formation of a fine crystalline deposit is a prerequisite for achieving good technical parameters of coatings, in particular equalization and gloss.

In practice, the combination of salts of organic acids such as acetic, benzoic and aromatic ketones such as acetophenone, diphenylketone has been widely used. However, these are not soluble in aqueous solutions and must be emulsified with suitable surfactants. For example, polyethylene glycols, ethylene oxide-propylene oxide copolymers, ethoxylated higher fatty alcohols and the like have proven to be useful.

Through the passage of the electroplating current, aromatic ketones are degraded and their decomposition products accumulate in the bath. Above a certain concentration, the leveling and gloss of the coatings, the hiding power and the ductility decrease and the internal stresses increase. The quality of the coatings thus deteriorates continuously, only the deposition of the coating on the metallized goods, with which a part of the impurities also leaves, is beneficial. If an economical non-flowable rinse or material closure of the circuit using special technology is included, the bath becomes degraded relatively soon.

The decomposition products are removed from the baths according to the best practice, generally oxidized with potassium permanganate and the reaction products are collected on activated carbon. This operation is technically and economically very demanding. The bath has to be taken out of operation, the electrolyte is lost as well as a partial decomposition of the brightening agents.

The described drawbacks are overcome by the solution according to the invention, which consists in adding aromatic azo compounds to the brightening agent containing aromatic ketones. Gloss-forming additive intended for the deposition of glossy zinc coatings up to 50 µm thickness consists of non-ionic surfactants prepared by ethylene oxidation of aliphatic alcohols of the general formula R - O- (CH ₂ CH ₂ O) _χ Η, where R is an alkyl of 8 to 20 carbons, x is an integer of 1 to 30, non-ionic surfactants prepared by copolymerization of ethylene oxide and propylene oxide of a molecular weight of 1 000 to 12 000, sodium or potassium salts of organic acids - acetic, benzoic, 4-methoxybenzoic and salicylic, aromatic ketones - acetophenone, methyl-2-naphthyl ketone , methylphenylketone and benzylidenaoetone and aromatic azo compounds of 4-dimethylaminoazobenzene, 4'-dimethylaminoazobenzene-3-sulfonic acid, 4'-dimethylaminoazobenzene-2-carboxylic acid and 4'-hydroxiazobenzene-4-sulfonic acid. The additive always contains at least one of the five compound groups, an organic solvent - ethanol, propanol, isopropanol or acetone, and water.

It has been found that this additive has the ability to allow the deposition of highly glossy, well-aligned, ductile coatings with minimal internal stress, porosity and good adhesion to the parent metal and, due to the aromatic azo compound content, to convert decomposition products resulting from electric current low harmful forms, which ensures long-term stability of coating parameters and minimal interruption of bath operation by cleaning operations.

A detailed explanation is given in the following examples.

Example 1

000 g of a brightener was prepared by mixing 220 g of a non-ionic surfactant with an 8-carbon alkyl and one ethoxy group per molecule, 300 g of ethylene-propylene oxide copolymers of MW. 1000, 10 g sodium 4-methoxybenzoate, 50 g benzylideneacetone and 0.1 g 4-dimethylaminoazobenzene, 300 g ethanol, 119.9 g water. This additive was dispensed into a galvanizing bath containing, in 1000 ml, 75 g of zinc chloride, 150 g of sodium chloride, 4 g of boric acid.

In the bath, steel test specimens were plated on hinges at a current density of 400 A per m @ 2, a voltage of 3.1 V and a temperature of 21 ° C for 30 minutes. Regular addition of 4 ml per 10 A.h resulted in a visible reduction in gloss and zinc coating after passing 170 to 200 A.h per 1,000 ml bath.

For comparison, a galvanizing bath containing a similarly prepared brightening agent, but without the aromatic azo compound, was loaded in the same way. A comparable decrease in gloss and leveling of zinc coatings occurred after passing 60-90 A.h per 1000 ml.

Example 2

000 g of a brightener was prepared by mixing 300 g of a non-ionic surfactant with an alkyl of 20 carbons and 24 ethoxy groups per molecule, 150 g of ethylene-propylene oxide copolymers of MW. 2,500, 100 g sodium acetate, 0.1 g acetophenone, 40 g benzylideneacetone, g 4'-dimethylaminoazobenzene-3-sulfonic acid, 300 g propanol and 108.9 g water. This additive was metered into the galvanic bath as in Example 1 in an amount of 4 ml per 1000 ml. The samples were also metallized as in Example 1. The gloss and leveling decreased in zinc coatings after passing 190 to 230 A.h per 1000 ml.

Example 3

000 g of a brightener was prepared by mixing 50 g of a non-ionic surfactant with an alkyl of 18 carbons and 30 ethoxy groups per molecule, 300 g of ethylene and propylene oxide copolymers of MW. 12,000, 1 g sodium benzoate, 60 g methylphenyl ketone, 0.03 g 4'-dimethylaminoazobenzene-2-carboxylic acid, 300 g isopropanol and 288.97 g water. This additive was metered into the galvanic bath as in Example 1 in an amount of 4 ml per 1000 ml. The samples were also metallized as in Example 1. The gloss and leveling decreased in zinc coatings after passing 150 to 180 A.h per 1000 ml.

Example 4

000 g of a brightener was prepared by mixing 200 g of a non-ionic surfactant with an alkyl of 8 carbons and 11 ethoxy groups per molecule, 50 g of ethylene-propylene oxide copolymers of MW. 12,000, 70 g of potassium salicylate, 100 g of methyl 2-naphthylketone,

0.01 g 4'-hydroxiazobenzene-4-sulfonic acid, 200 g acetone and 371.99 g water. This additive was metered into the galvanic bath as in Example 1 in an amount of 4 ml per 1000 ml. Plating samples were as in Example 1. The decrease in gloss and the leveling of zinc coatings occurred after the passage of 160 to ¹ 190 Ah per 1000 ml.

The invention can be used in the galvanizing of products in the field of engineering and electrotechnical companies and production cooperatives.

Claims (1)

object of the invention Gloss-forming additive for electrolytic deposition of zinc coatings up to 50 µm thick from weakly acidic zinc baths containing ammonium salts, consisting of zinc chloride or ammonium chloride, or without ammonium salts, consisting of zinc chloride or sulfate, sodium or potassium chloride and borates, containing nonionic surfactants prepared by ethylene oxidation of aliphatic alcohols, nonionic surfactants prepared by copolymerization of ethylene oxide and propylene oxide, salts of organic acids and aromatic ketones, characterized in that it consists of - 5 to 30 wt. nonionic surfactants of the general formula R-O-IC (CH3O) _χ Η, where R is an alkyl of 8 to 20 carbons, x is an integer of 1 to 30 - 5 to 30 wt. nonionic surfactants prepared by copolymerization of ethoxide and propylene oxide of molecular mass 1 000 to 12 000 0.1 to 10 wt. sodium or potassium salts of acetic, benzoic, 4-methoxybenzoic or salicylic acid 0.01 to 10 wt. acetophenone,. methyl 2-naphthylketone, methylphenylketone or benzylidene acetone 20 to 40 wt. ethanol, propanol, isopropanol or acetone - 10 to 50 wt. water and further contains 0.01 to 0.1 wt. 4-dimethylaminoazobenzene, 4-dimethylaminoazobenzene-3-sulfonic acid, 4'-dimethylamino-azobenzene-2-carboxylic acid or 4'-hydroxiazobenzene-4-sulfonic acid, each containing at least one of the abovementioned compound groups.