Electrodeposition of zinc and additive therefore

In an aqueous alkaline, cyanide-free zinc electroplating bath containing zinc ions and hydroxyl ions, the improvement comprising:

• including in said bath an effective brightening amount of
• a. at least one linear polyamine obtained by condensing a diamine of the formula:
• ##STR6## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4, which may be the same or different, each represent a hydrogen atom or an alkyl group with 1 to 4 carbon atoms, and where m is an integer from 1 to 5, with a dihalide of the formula
• X -- (CH.sub.2).sub.n -- Y -- (CH.sub.2).sub.p -- X (II)
• where X represents a halogen atom, Y represents an oxygen atom, an ethynylene group (--C.dbd.C--), an ethenylene group (--HC.dbd.CH--), or a group ##STR7## where Z represents a hydrogen atom, an alkyl group with 1 to 4 carbon atoms or a hydroxy group, and n and p, which may be the same of different, are zero or an integer from 1 to 5;
• provided that when Z represents a hydroxy group and n and p are both 1, R.sup.1 and R.sup.2 in formula (I) both represent hydrogen atoms;
• together with
• b. at least one of a pyridine compound of formula IIIa or a pyridine compound having a cation of formula III (b) ##STR8## where R.sup.5 represents a hydrogen atom or an alkyl group with 1 to 5 carbon atoms;
• and R.sup.6 represents a cyano group, a group -COOR.sup.7 where R.sup.7 represents a hydrogen atom, an alkali metal cation or an alkyl group with 1 to 5 carbon atoms;
• or a group --CONR.sup.8 R.sup.9 where R.sup.8 and R.sup.9 which may be the same or different each represents a hydrogen atom or an alkyl group with 1 to 5 carbon atoms;
• and R.sup.10 represents a radical selected from the group consisting of aralkyl, alkyl, alkenyl, esterified carboxyalkyl and hydroxyalkyl groups.

A brightener composition for addition to an alkaline, cyanide-free zinc electroplating bath, comprising a mixed solution of

• a. at least one linear polyamine obtained by condensing a diamine of the formula:
• ##STR9## where R.sup.1, R.sup.2, R.sup.3 and R.sup.4, which may be the same or different, each represents a hydrogen atom or an alkyl group with 1 to 4 carbon atoms, and where m is an integer from 1 to 5, with an alkyl dihalide of the formula
• X -- (CH.sub.2).sub.n -- Y -- (CH.sub.2).sub.p -- X (II)
• where X represents a halogen atom;
• Y represents an oxygen atom, an ethynylene group (--C.dbd.C--), an ethenylene group (--HC.dbd.CH--), or a group ##STR10## where Z represents a hydrogen atom, an alkyl group with 1 to 4 carbon atoms or a hydroxy group, and n and p, which may be the same different, are zero or an integer from 1 to 5;
• provided that when Z represents a hydroxy group, n and p are both 1 and R.sup.1 and R.sup.2 in formula (I) both represent hydrogen atoms;
• and
• b. at least one of a pyridine compound of formula IIIa or a pyridine compound having a cation of formula IIIb ##STR11## where R.sup.5 represents a hydrogen atom or an alkyl group with 1 to 5 carbon atoms;
• and R.sup.6 represents a cyano group, a group -COOR.sup.7 where R.sup.7 represents a hydrogen atom, an alkali metal cation or an alkyl group with 1 to 5 carbon atoms;
• or a group CONR.sup.8 R.sup.9 where R.sup.8 and R.sup.9 which may be the same or different each represents a hydrogen atom or an alkyl group with 1 to 5 carbon atoms and R.sup.10 represents an aralkyl, alkyl, alkenyl, esterified carboxyalkyl or hydroxyalkyl group.