US3915815A

US3915815A - Alkaline zinc electroplating bath

Info

Publication number: US3915815A
Application number: US415757A
Authority: US
Inventors: Reinhard Koch
Original assignee: Individual
Current assignee: Individual
Priority date: 1972-11-15
Filing date: 1973-11-14
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

The alkaline zinc electroplating bath of the present invention contains as brightening agent the reaction product of A. POLYETHYLENE IMINE OR POLYPROPYLENE IMINE WITH B. AN AROMATIC ALDEHYDE, C. AMMONIA AND/OR ETHYLENEDIAMINE, OR DIETHYLENE TRIAMINE AND D. EPICHLOROHYDRIN. Due to the addition of said reaction product its cyanide content can be considerably reduced without impairing the brightness of the zinc deposit.

Description

United States Patent Koch Oct. 28, 1975 [54] ALKALINE ZINC ELECTROPLATING BATH 3,472,743 10/1969 Rushmere 204/55 Y 3,655,534 4/1972 Kampe [76] Inventor Remha'd Koch 6081 Gemshem" 3,806,431 4/1974 Koch 204/55 Y Germany [22] Filed: Nov. 14, 1973 Primary Examiner-G. L. Kaplan [2U Appl No 415,757 Attorney, Agent, or FirmErich M. H. Radde [301 Foreign Application Priority Data [57] ABSTRACT Nov. 15, 1972 Germany 2256000 The alkaline Zine electroplating bath of the Pleserlt vention contains as brightening agent the reaction 52 us. c1. 204 55 Y; 260/292 EP; 260/72 R product of [51] Int. C1. C25D 3/24 P y y mine or P yp py mine with 58 Field of Search 204/55 Y, 55 R, 432, 44 an aromatic aldehyde.

c. ammonia and/or ethylenediamine, or diethylene References Cited triamine and UNiTED STATES PATENTS eplchlmhydm- 2288318 6/1942 Hoffman 204,55 Y Due to the addition of said reaction product its 2,630,712 6/1954 Diggin et a1 204,55 Y cyanide content can be considerably reduced without 2,791,554 5 1957 Winters 204/55 Y impairing the g ne f h zin p i 2,860,089 11/1958 Jackson 204/55 Y 3,227,638 1/1966 Burnson 204/55 Y x 9 Clams, N0 Drawmgs ALKALINE ZINC ELECTROPLATING BATH BACKGROUND OF THE INVENTION 1. Field of the Invention bath and more particularly to a The present invention relates to a cyanide-containing zinc electroplating bath cyanide-containing zinc electroplating bath yielding smooth and bright to fully bright zinc plates, to a process of producing said baths, and to a method of using such baths for electroplating.

2. Description of the Prior Art Cyanide-containing zinc baths for electrolytic deposition of zinc plates are known. Bright zinc plates of excellent throwing power, metal distribution, and brilliance are produced, when using such baths.

Cyanide-containing Zinc baths require the addition of special brightening additives in order to produce zinc layers of high brilliance. Such additives are, for instance, amino-aldehyde derivatives such as aldehydealkanolamines, water-soluble polyvinyl alcohols, salts of metals of the groups VIIB or VIII of the Periodic System, and sugars. The amounts of such additives, however, must be carefully adjusted in relation to the zinc content and/or the cyanide content of the bath.

More recently, and in ever increasing numbers, weakly acid or alkaline cyanide-free zinc baths or baths of a low cyanide content are used in order to meet the requirements of pollution control which demands special waste disposal treatment and equipment so as to conform with legal provisions. However such cyanidefree zinc baths or baths of a low cyanide content usually do not yield zinc coating of a brilliance comparable to that attained with cyanide-containing zinc baths.

SUMMARY OF THE INVENTION It is one object of the present invention to provide a novel and advantageous cyanide-containing zinc bath and especially a zinc bath of a low cyanide content which yields bright zinc coatings, has a satisfactory throwing power, and achieves good metal distribution, said bath exhibiting the properties of a good zinc bath of the usual high cyanide content, said bath permitting to considerably decrease its cyanide content even when operating at a current density below I amp./sq.dm.

Another object of the present invention is to provide a simple and effective process of producing such a zinc bath.

A further object of the present invention is to use such a zinc bath for zinc electroplating and the deposition of a bright zinc coating.

Other objects of the present invention and advantageous features thereof will become apparent as the description proceeds.

In principle the bright zinc plating bath according to the present invention contains, in addition to an alkali metal hydroxide, cyanide and zinc as suitable, salts to form zincate and complex zinc cyanide ions, polyvinylalcohol or acetyl derivatives thereof, and if desired, salts of metals of the Groups VII B and VIII of the Periodic System, and a monosaccharide or polysaccharide, as they are present in the known bright zinc electroplating baths, a reaction product of a. a polyalkylene imine such as polyethylene imine or polypropylene imine with b. an aromatic aldehyde, c. ammonia and/or ethylenediamine and diethylene triamine respectively, and

d. epichlorohydrin. Said reaction product is prepared by first reacting componentsta) and (b) in an aqueous medium, such as water at a temperature between 20C. and 50C., adding component (c) and subsequentlyadding component (d) and heating the reaction mixture to a temperature of between 30C. and 60C., if desired, with further dilution of the reaction mixture with water. The solution of the reaction product obtained may be used without separating the reaction product. The amounts of said reaction product (calculated as non-aqueous product) added to the zinc plating bath are between 0.1 g./l. and 10 g./l., preferably between 0.2 g./l. and 5.0 g./l. of zinc bath. The amounts of zinc are normally between 5 g./l. and 50 g./l. and the amounts of cyanide are between 5 g./l. and g./l. of zinc bath. Such a bath has an alkali metal cyanide: Zinc ratio (M-factor) between 1 and 3.2.

As aromatic aldehydes, there are preferably used benzaldehydes, halogenor hydroxyl-substituted benzaldehydes such as 2,4-dichlorobenzaldehyde, phydroxy benzaldehyde, and other aldehydes of the general formula CHO In said formula R indicates hydroxyl and/or lower alkoxy with l to 4 carbon atoms and especially methoxy, while X indicates one of the numerals 0, l, or 2. Preferred aldehydes of this type are salicylaldehyde, anisaldehyde, vanillin, and veratraldehyde. The molecular proportions of the components of the brightening reaction product added to the zinc plating bath are preferably as follows: 7

Molecular proportion of polyethylene imine or respectively, polypropylene imine to aromatic aldehyde between about 1:: l and l 15;

molecular proportion of polyethylene imine or, re-

spectively, polypropylene imine to epichlorohydrin between about 1 3 and about 1 40;

molecular proportion of ammonia or, respectively,

ethylene diamine or diethylene triamine to epichlorohydrin I l.

Salts of manganese or nickel are preferably used as salts of a metal of the Groups VIIB or VIII of the Periodic System. They are employed in amounts between 0.01 g./l. and 0.1 g./l. and preferably between 0.01 g./l. and 0.05 g./l.

Polyvinylalcohol or an acetyl derivative thereof having a degree of polymerisation between about 300 and about 1500, such as sold under the tradename Mowiol by Farbwerke I-Ioechst is added in an amount between 0.05 g./l. and 0.5. g./l. and preferably in an amount between 0.l g./l. and 0.5 g./l.

As monoand polysaccharides one or several of dextrose, glucose, saccharose and dextrines are preferably added in an amount between 0.01 g./l. and 0.08 g./l.

"DESCRIPTION or THE PREFERRED EMBODIMENTS EXAMPLE 1 Smooth and even, bright zinc deposits on iron are obtained with a bath of the following composition, said bath having excellent throwing power, metal destribution, and brilliance. The amounts of its components are given as amounts in grams per liter of bath:

Zinc calculated as zinc oxide Sodium cyanide Sodium hydroxide Reaction product of a. polyethylene imine, b. veratraldehyde, c. ammonia, and d. epichlorohydrin in the following proportions:

(a) (b) l:l moles; (a) I (d) 1:3 moles; (C) (d)= 1:] moles Polyvinylalcohol (Mowiol N 30-88) Dextrose Manganese sulfate Nickel sulfate 0.2 g. to 5.0 g. 0.05 g. to 0.5 g. 0.5 g. to 5.0 g.

Such a bath is used at a bath temperature between C. and 35C.

The current density is between 0.3 amp./sq.dm. and 5.0 Amp./sq./dm.

EXAMPLE 2 Smooth and even, bright zinc coatings on iron are produced with the following bath having an excellent throwing power, metal inhibition, and brilliance. The amounts of the components are calculated as amounts in grams per liter of bath:

7 g. to g. 81.5 g. 95 g.

Zinc (calculated as zinc oxide) Sodium cyanide.

Sodium hydroxide.

Reaction product made from g 0.05 g. to 0.5 g.

Such a bath is used at a bath temperature between 15C. and C.

The current density is between 0.3 Amp./sq.dm and 5.0 Amp/sq. dm.

EXAMPLE 3 The reaction product of the polyalkylene imine, an aromatic aldehyde, ethylene diamine and/or ammonia, and epichlorohydrin is prepared as follows:

25 g. (0.01 mole) of polyethylene imine are reacted with 53 g. (0.5 mole) of benzaldehyde with the addition of 50 cc. of water at a temperature of 50C. within about 30 minutes. The reaction mixture is cooled to room temperature. 24 g. (0.4 mole) of ethylene diamine are added thereto and the resulting mixture is made up with water to 300 cc. Thereafter, there are added portion by portion 2.76 g. to 27.6 g. (0.03 mole to 0.3 mole) and subsequently 36.8 g. (0.4 mole) of epichlorohydrin in such a manner that the reaction temperature does not exceed a temperature of 60C. The reaction mixture is then made up with water to one liter.

Polyethylene imine can be replaced in said example by the equivalent amount of polypropylene imine.

In place of ethylene diamine, there can also be used 40 cc. of a 36% ammonia solution.

The benzaldehyde can be replaced by equimolecular amounts of other aromatic aldehydes.

I claim:

1. In an alkaline zinc electroplating bath comprising, in aqueous solution, a zinc salt, an alkali metal cyanide, an alkali metal hydroxide, and a water-soluble polyvinylalcohol, the improvement which comprises said bath containing, as brightening agent, between about 0.1 g./l. and about 10.0 g./l. of the reaction product obtained by reacting in an aqueous medium at a temperature between about 20 and 50C.

a. a polyalkylene imine selected from the group consisting of polyethylene imine and polypropylene imine, with b. an aromatic aldehyde, in a molar ratio between about 1:1 to 1:50 of imine to aldehyde, adding c. a basic agent selected from the group consisting of ammonia, ethylene diamine, and diethylene triam' ine, and

d. epichlorohydrin, in a molar ratio between about 1:3 to 1:40 of imine to epichlorohydrin and about 1:1 of basic agent to epichlorohydrin, and heating the reaction mixture.

2. The zinc electroplating bath of claim 1 additionally containing a salt of a metal selected from the group consisting of a metal of the Groups VllB and VIII of the Periodic System.

3. The alkaline zinc electroplating bath of claim 2, wherein said metal salt is present in an amount of between about 0.01 and 0.1 g./l.

4. The zinc electroplating bath of claim 1 additionally containing a monoor polysaccharide.

5. The alkaline zinc electroplating bath of claim 3, wherein said monoor poly-saccharide is present in an amount of between about 0.01 and 0.08 g./l.

6. The zinc electroplating bath of claim 1 additionally containing a salt of a metal selected from the group consisting of a metal of the groups VllB and VIII of the Periodic System and a monoor polysaccharide.

7. The alkaline zinc electroplating bath of claim 6, wherein said metal salt is present in an amount of between about 0.01 and 0.1 g./l. and said monoor polysaccharide is present in an amount between about 0.01 and 0.08 g./l.

8. The zinc electroplating bath of claim 1, in which the aromatic aldehyde component of the reaction product is an aromatic aldehyde selected from the group consisting of benzaldehyde, a halogen-substituted benzaldehyde, a hydroxyl-substituted benzaldehyde, atoms and and an aromatic aldehyde of the formula X is a numeral selected from the numerals of 0, l,

and 2. 9. The alkaline zinc electroplating bath of claim 1, in CH which said bath contains, as brightening agent, between about 0.2 g./l. and about 5.0 g./l of the reaction product X Of a. a polyalkylene imine selected from the group consisting of polyethylene imine and polypropylene 1O imine, with b. an aromatic aldehyde,

- c. a basic agent selected from the group consisting of in which ammonia, ethylene diamine, and diethylene triam- R is a member selected from the group consisting of ine, and

hydroxyl and lower alkoxy with l to 4 carbon d. epichlorohydrin.

UNITED STATES PATENT OFFICE CERTIFHIATE OF CQHRECTION Patent No. 3,915,815 Dated October 28, 1975 Inventor) REINHARD KOCH It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Column 1, line 6: "bath and more particularly" should be cancelled.

Q line 7: "to a" should be cancelled.

line 8: After "bath" there should be added and more particularly to a Signed and Sealed this tenth Day Of February 1976 [SEAL] Arrest:

RUTH C. MA SON C. MARSHALL DANN Allemn g Officer Commissioner oj'Parents and Trademarks

Claims

1. IN AN ALKALINE ZINC ELECTROPLATING BATH COMPRISING, IN AQUEOUS SOLUTION, A ZINC SALT, AN ALKALI METAL CYANIDE, AN ALKALI METAL HYDROXIDE, AND A WATER-SOLUBLE POLYVINYLALCOHOL, THE IMPROVEMENT WHICH COMPRISES SAID BATH CONTAINING, AS BTIGHTENING AGENT, BETWEEN ABOUT 0.1 G./1. AND ABOUT 10.0 G/1. OF THE REACTION PRODUCT OBTAINED BY REACTING IN AN AQUEOUS MEDIUM AT A TEMPERATURE BETWEEN ABOUT 20* AND 50*C. A. A POLYALKYLENE IMINE SELECTED FROM THE GROUP CONSISTING OF POLYETHYLENE IMINE AND POLUPROPYLENE IMINE, WITH B. AN AROMATIC ALDEHYDE, IN A MOLAR RATIO BETWEEN ABOUT 1:1 TO 1:50 OF IMINE TO ALDEHYDE, ADDING C. A BASIC AGENT SELECTED FROM THE GROUP CONSISTING OF AMMONIA, ETHYLENE DIAMINE, AND DIETHYLENE TRIAMINE, AND D. EPICHLOROHYDRIN, IN A MOLAR RATIO BETWEEN ABOUT 1:3 TO 1:40 OF IMINE TO EPICHLOROHYDRIN AND ABOUT 1:1 OF BASIC AGENT TO EPICHLOROHYDRIN, AND HEATING THE REACTION MIXTURE.

2. The zinc electroplating bath of claim 1 additionally containing a salt of a metal selected from the group consisting of a metal of the Groups VIIB and VIII of the Periodic System.

4. The zinc electroplating bath of claim 1 additionally containing a mono- or polysaccharide.

5. The alkaline zinc electroplating bath of claim 3, wherein said mono- or poly-saccharide is present in an amount of between about 0.01 and 0.08 g./l.

6. THE ZINC ELECTROPLATING BATH OF CLAIM 1 ADDITIONALLY CONTAINING A SALT OF A METAL SELECTED FROM THE GROUP CONSISTING OF A METAL OF THE GROUPS VIIB AND VIII OD THE PERIODIC SYSTEM AND A MONO-OR POLYSACCHARIDE.

7. The alkaline zinc electroplating bath of claim 6, wherein said metal salt is present in an amount of between about 0.01 and 0.1 g./l. and said mono- or poly-saccharide is present in an amount between about 0.01 and 0.08 g./l.

8. The zinc electroplating bath of claim 1, in which the aromatic aldehyde component of the reaction product is an aromatic aldehyde selected from the group consisting of benzaldehyde, a halogen-substituted benzaldehyde, a hydroxyl-substituted benzaldehyde, and an aromatic aldehyde of the formula

9. The alkaline zinc electroplating bath of claim 1, in which said bath contains, as brightening agent, between about 0.2 g./l. and about 5.0 g./l of the reaction product of a. a polyalkylene imine selected from the group consisting of polyethylene imine and polypropylene imine, with b. an aromatic aldehyde, c. a basic agent selected from the group consisting of ammonia, ethylene diamine, and diethylene triamine, and d. epichlorohydrin.