PL179068B1 - Bath for chromating electrodeposited zinc coatings - Google Patents

Abstract

A bath for chromating zinc coatings, containing as the main component 5.0-50.0 g / dm3 of chromate (VI) ions, 1.0-75.0 g / dm3 of mineral and / or organic acids and / or sodium salts of these acids and 1.0-5.0 g / dm3 of surfactants, characterized in that it contains 1.0-10.0 g / dm3 of catalyst selected from acid Sodium 3-hydroxy-2,7-naphthalenedisulfonyl or sodium 3-hydroxy-2,7-naphthalenedisulfbate acid Sodium 7-hydroxy-1,3-naphthalenedisulfonic acid or sodium 7-hydroxy-1,3-naphthalenebdl sulfbate, Sodium 6-hydroxy-2-naphthalenesulfonic acid or sodium 6-hydroxy-2-naphthalenesulfonate, or mixtures of 3-hydroxy-2,7-naphthalenesulfonic acid 7-hydroxy-1,3-naphthalenedisulfonic acid together with 6-hydroxy-2-naphthalenesulfonic acid.

Description

The subject of the invention is a bath for chromating zinc coatings yellow.

The baths used for chromating zinc coatings contain as a basic component chromate (VI) ions, introduced into the bath in the form of chromic anhydride, chromium (VI) trioxide - CrO3 and / or salts such as sodium dichromate - Na ₂ Cr2O7 dichromate (VI) ammonium - (NH ₄ ) ₂ Cr ₂ O ₇ and zinc dichromate (VI) - ZnCr ₂ O ₇ , in amounts up to 250 g / dm3. Chromating baths contain mineral acids and / or salts such as sulfuric (VI), phosphoric (V), nitric (V), boric, fluoroboric, sulphates (VI), phosphates (V), hydrogen phosphates (V), nitrates ( V), chlorides, fluorides, organic acids such as acetic acid, formic acid, oxalic acid, citric acid, and compounds with surfactant properties. Some baths additionally contain metal ions such as iron, cobalt, nickel, manganese, molybdenum, aluminum, lanthanum, cerium or mixtures of these.

There are also known baths for chrcmiancwama, in which the basic ingredient is chiOmu (III) ions, usually introduced in the form of chromium (III) sulfate (III) - Cr ₂ (SOO3 or chromium (III) and potassium sulfate (VI) - KCr (SO4h) As in the previous baths, these baths also contain - mineral and organic acids, salts, surfactants and metal ions. Additionally, they must contain compounds with properties that oxidize chromium (IIJ) ions to chromate (VI) ions, most often nitrate ( V) sodium.

There are also known baths for zinc coating, containing chromate (VI) ions, introduced into the bath in the form of chromic anhydride and / or dichromate (VI), and compounds with reducing properties, such as sodium or potassium sulphates (IV) or hydrogen sulphate (IV). , saccharides. These compounds reduce chromate (VI) ions to chromium (III) ions. Also in this type of baths, mineral and organic acids, salts and active surfactants are additionally used.

Chromating bath for zinc coatings, containing as the main component 5.0-50.0 g / dm3 of chromate (VI) ions, introduced as chromic anhydride (Cr03) and / or sodium dichrcmate (VI) (Na2Cr ₂ O7), as additional ingredients the bath contains 1.0-75.0 g / dm3 of mineral and / or organic acids and / or sodium salts of these acids and 1.0-5.0 g / day of the surface compounds according to the invention additionally contains

1.0-10.0 g / dm3 of the catalyst selected from 3-hydroxy-2,7-naphthalenedisulfonic acid or sodium 3-hydroxy-2,7-naphthalenedisulfonate, 7-hydroxy-1,3-naphthalenedisulfonate or 7-hydroxy- Sodium 1,3-naphthalene sulfonate, 6-hydroxy-2-naphthalene sulfonic acid or sodium 6-hydroxy-2-naphthalenesulfonic acid or a mixture of 3-hydroxy-2,7-naphthalenedisulfonic acid 7-hydroxy-1,3-naphthalenedisulfonic acid together with 6-hydroxy-2-naphthalenesulfonic acid.

The above-mentioned hydroxynaphthalenesulfonic acids and a mixture of these acids were obtained by sulfonating β-naphthol with 98% sulfuric acid at temperatures from 288K (15 ° C) to 395K (122 ° C).

The bath according to the invention is characterized by durability, stability of operation and the ability to form a yellow chromate coating resistant to corrosion.

Example.

The chromating bath was prepared containing 35.0 g / dm ³ of chromate ions (VI) 10.0 g / dm3 of sulfate ions (VI) is introduced in the form of sulfuric acid (VI) 10.0 g / dm3 of nitrate ions (V) introduced in the form of nitric acid, 15.0 g / dm3 of phosphate (V) ions introduced in the form of orthophosphoric (V) acid, 10.0 g / dm3 of acetate ions introduced as acetic acid or sodium acetate, and

2.5 g / dm3 of surfactants introduced in the form of "Rokanol" or "Rokafenol" preparations. The catalyst used was successively 3-hydroxy-2,7-naphthalenedisulfonic acid, sodium 6-hydroxy-2-naphthalenesulfonate, 7-hydroxy-1,3-naphthalenedisulfonic acid, sodium 7-hydroxy-1,3-naphthalenedisulfonate, 6-hyairoxy acid Sodium -2-naphthalenesulfonic, 6-hydroxy-2-naphthalenesulfonate and a mixture of the above-mentioned acids in the amount of 4.0 g / dm3.

In the above-mentioned baths, zinc coatings were subjected to chromating, immediately after their deposition from the alkaline zinc bath. The chromate coatings were yellow, uniformly shiny, without stains and stains. After chromating, the samples were tested in a salt chamber, in neutral salt spray (NSS), at the temperature of 308K (35 ° C), according to the Polish Standard PN-76 / H-04603. The first signs of corrosion were observed after approximately 180 hours of salt spray test.

179 068

Publishing Department of the UP RP. Circulation of 60 copies

Price PLN 2.00.

Claims (1)

Patent claim A bath for chromating zinc coatings, containing as the main component 5.0-50.0 g / dm ³ of chromate (VI) ions, 1.0-75.0 g / dm ³ of mineral and / or organic acids and / or sodium salts of these acids and 1.0-5.0 g / dm3 of surfactants, characterized in that it contains 1.0-10.0 g / dm3 of a catalyst selected from 3-hydroxy-2,7-naphthalenedisulfonic acid or 3-hydroxy-2 , Sodium 7-naphthalenedisulfonate, 7-hydroxy-1,3-naphthalenedisulfonic acid or sodium 7-hydroxy-1,3-naphthalene disulfonate, sodium 6-hydroxy-2-naphthalenesulfonic acid or sodium 6-hydroxy-2-naphthalenesulfonate or a mixture of 3- 7-hydroxy-1,3-naphthalenedisulfonic acid hydroxy-2,7-naphthalenedisulfonic acid together with 6-hydroxy-2-naphthalenesulfonic acid.