US3823076A - Zinc electroplating additive - Google Patents

Abstract

AQUEOUS ADDITION AGENTS FOR ZINC ELECTROPLATING BATHS ARE PROVIDED WHICH HAVE DISSOLVED THEREIN (A) A PYRIDINIUM COMPOUND OF THE GENERAL FORMULA:

1-R'',3-R-PYRIDINIUM X(-)

WHEREIN R IS -CONH2,-CN,-CHO OR -COOR", R'' IS AN ALKYL GROUP OF 1-4 CARBON ATOMS, -CH2CH=CH2,-CH2C=CH, -CH2CH=CHCH2X, -CH2COOR" OR

-CH2-CH=CH-CH2-(3-R-PYRID-1-YL) X(-)

R" IS AN ALKYL GROUP OF 1-4 CARBON ATOM, AND X-IS A HALOGEN ION, AND (B) A POLYSTYRENESULFONATE, A POLYVINYLPYRROLIDONE, A POLYOOXYALKYLDIAMINE, A WATER-SOLUBLE QUATERIZED CONDENSATION PRODUCT OF AN EPIHALOHYDRIN AND A POLYAMINE, OR A WATER-SOLUBLE CONDENSATION PRODUCT OF A BENZENE OR A NAPHTHALENE SULFONIC ACID, OR A SALT THEREOF, WITH FORMALDEHYDE, SAID CONDENSATION PRODUCT CONTAINING AT LEAST 2 BENZENE OR NAPHTHALENE SULFONIC ACID GROUP CONNECTED WITH EACH OTHER BY METHYLENE BRIDGES.

Description

United States Patent 3,823,076 ZINC ELECTROPLATING ADDITIVE John Derek Rushmere, Wilmington, Del., assignor to E. I.

du Pont de Nemonrs and Company, Wilmington, Del. No Drawing. Continuation-impart of application Ser. No.

256,179, May 23, 1972, now Patent No. 3,769,184.

This application May 2, 1973, Ser. No. 356,432

Int. Cl. C23b 5/12, 5/46 US. Cl. 204-55 R 3 Claims ABSTRACT OF THE DISCLOSURE Aqueous addition agents for zinc electroplating baths are provided which have dissolved therein (a) a pyridinium compound of the general formula:

wherein R is CONH CN, CHO or COOR"; R is an alkyl group of 1-4 carbon atoms,

CH CH=CH CHZCECH,

CH CH=CHCH X, CH COO'R" or R is an alkyl group of 1-4 carbon atoms; and X- is a halogen ion; and

CROSS REFERENCE TO RELATED APPLICATION This is a continuation-in-part of application Ser. No. 256,179, filed May 23, 1972, assigned to the assignee of the present application and now US. Pat. No. 3,769,184.

BACKGROUND OF THE INVENTION Field of Invention This invention relates to zinc electroplating baths and processes, and additives useful therein, and, more particularly, to such baths and processes for depositing bright zinc plates.

Prior Art Numerous patents concerned with bright zinc deposits obtained from acid zinc baths have issued over the years. US. Pat. 3,537,959, issued Nov. 3, 1970, to Joachim Korpiun and Hans J. Steeg, is directed to the co-use of primary amines and naphthalene sulfonic acid-formaldehyde condensation products for this purpose. The co-use of quaternized pyridines with linear polyethers for acid zinc plating is disclosed in German Pat. 2,111,602, published Mar. 18, 1970. My copending application Ser. No. 157,662, filed June 28, 1971, discloses the use of certain quaternized pyridine compounds in acid zinc plating. Other patents directed to the use of sulfur and nitrogen compounds include US. Pat. 2,355,505, issued to John L.- Bray and Robert E. Howard on Aug. 8, 1944, and US.

3,823,076 Patented July 9, 1974 "ice Pat. 2,543,545, issued to Charles L. Faust and Arthur E. Bearse on Feb. 27, 1951, which discloses the use of sulfonated heterocyclics.

Quaternary pyridine compound additives useful in alkaline cyanide zinc plating are described in US. Pat. 3,318,- 787, issued to Gustav Rindt and Donald H. Becking on May 9, 1967, and certain pyridinium compounds useful in alkaline zinc plating are described in US. Pat. 3,411,996, issued to John D. Rushmere on Nov. 19, 1968.

SUMMARY OF THE INVENTION According to the present invention there is provided an addition agent for an aqueous zinc electroplating bath comprising an aqueous solution containing (a) about 1-25 percent by weight of a pyridinium compound of the general formula:

wherein R is CONH CN, CHO or COOR; R is an alkyl group of 1-4 carbon atoms,

R" is an alkyl group of 1-4 carbon atoms; and X- is a halogen ion; and

DETAILED DESCRIPTION OF THE INVENTION This invention pertains to the electrodeposition of zinc from zinc plating baths known to those skilled in the art. These baths may be formed by the dissolution of zinc oxide in common industrial acids such as hydrochloric, sulfuric, sulfamic and fluoboric. More commonly, however, the baths are formed by the dissolution of commercial zinc and ammonium salts such as the sulfates, chlorides, acetates, fluoborates or sulfamates in Water with subsequent adjustment of pH to the normal or desired range by means of aqueous ammonia, ammonium hydrox' ide or other bases, or an acid as required.

While the bath pH will generally be at a slightly acidic pH between 3.5- and 6.5, a higher pH bath, such as to pH 7.5, may be used, by the addition of a base such as ammonium hydroxide. However, for this invention, it is preferred to operate at a pH between 5 and 6.5 when using the preferred zinc chloride baths.

In zinc chloride baths, ammonium chloride is added to improve electrical conductivity and to help complex zinc ions, thereby increasing both throwing power and high temperature operability. Zinc metal content of the bath will range from about 545 g./l., preferably 5-20 g./1., most preferably 6-9 g./l. The Cl/Zn weight ratio will range between about 4/1 and 30/1 depending on the zinc metal content of the bath, the ratio being limited by bath temperature and ammonium chloride solubility. Thus, very good performance using the additives of this invention can be obtained from a bath containing 15 g./l. Zn, Cl/Zn ratio of 10/1, pH 5.1, and temperature of operation 10-45 C., preferably 20-30 C. A further improvement in performance can be obtained by using a bath containing 7.5 g./l. Zn, Cl/Zn ratio of 25-30/ 1, pH 6.1, and temperature of operation 10-50 0, preferably 20-45 C.

Bath formulations may contain mixtures of zinc salts such as zinc chloride and zinc sulfate. However, there appears to be little practical advantage for doing this. Bath formulations may also contain other metal salts such as a conductivity increasing salt, like sodium sulfamate or potassium sulfate.

Zinc deposits obtained from such acid baths without additives are typically coarse and dull gray in appearance and have little commercial value, especially in decorative plating of screws, chains and other items of hardware. It has now been found that when an additive combination comprising a mixture of certain quaternized pyridine compounds with a polystyrenesulfonate, a polyvinylpyrrolidone, a polyoxyalkyldiamine, a water soluble quaternized condensation product of an epihalohydrin and a polyamine, or water-soluble condensation products of an aryl sulfonic acid with formaldehyde is added to the acid zinc bath, bright, shiny zinc of high decorative quality can be obtained from both barrel plating and rack plating operations. The pyridinium compounds useful in the present invention have the [general formula:

p wherein R is -CONH CN, CHO or COOR"; R' is an alkyl group of 1-4 carbon atoms,

R" is an alkyl group of 1-4 carbon atoms; and

X is a halogen ion, preferably chlorine, bromine or iodine.

The pyridim'um compound is used at a concentration level of about 0.02 to 20 grams per liter, preferably about 0.05

to 5 grams per liter.

Preferred pyridinium compounds are l-allyl, 3-carboxamido pyridinium halide where the halide is chloride, bromide or iodide. Other compounds that have been found useful include:

The second component of the additive is a polystyrenesulfonate, a polyvinylpyrrolidone, a polyoxyalkyldiamine,

a water-soluble quaternized condensation product of an epihalohydrin and a polyamine, or a water-soluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof (usually alkali metal), with formaldehyde containing at least two benzene or naphthalene sulfonic acid groups which are connected with each other by means of methylene bridges. A naphthalene sulfonic acid is preferred. Preparation of these products is known and one such method is mentioned in US. Pat. 3,537,959. The second component is added in an amount to give a bath concentration of about 0.5 to 50 grams per liter, preferably about 1 to 20 grams per liter. The particular concentration used and found effective will depend upon the type and amount of pyridinium compound used and whether rack or barrel plating is being used.

The brightener combination of the present invention is preferably and effectively used as an aqueous solution addition agent containing about 1 to 25 percent by weight, preferably about 1 to 10 percent, of the pyridinium compound and about 1 to 50 percent by weight, preferably about 1 to 20 percent, of the condensation product. A particularly effective addition agent uses l-allyl, 3-carboxamido pyridinium chloride as the pyridinium compound and the sodium salt of a naphthalene sulfonic acid-formaldehyde condensation product. The addition agent is normally used by adding about 5 to 20 ml. of solution per liter of bath although larger amounts (such as up to 50 ml./l. can be used with effectiveness).

The invention can be further understood by referring to the examples in which parts and percentages are by weight unless otherwise indicated.

In conducting the following examples, a basic zinc chloride bath containing:

ZNCl

g /l 32 NH Cl g /1 200 pH 5.1

was used unless otherwise noted. Temperature of operation was 2228 C. again unless otherwise noted.

EXAMPLE 1 A steel Hull Cell panel was plated at 2 amps for 5 minutes in the basic bath containing 2.0 g./l. Darvan #1 and 2.0 g./1. l-propargyl, S-car-boxamido pyridinium bromide.

Very bright plate free of pits was obtained over the current density range 2-60 amps/ft.

EXAMPLE 3 To a 4-liter basic zinc chloride bath were added 65 cc. of an aqueous brightener containing 15 percent of a watersoluble condensation product between alkyl naphthalene sulfonic acid and formaldehyde (Daxad 1 1) and 6 percent 1-al1yl, 3-carboxamido pyridinium bromide. An automobile steel crank hold cover, a shape comprising both concave and convex surfaces, was still plated with no agitation at 2 amps for 20 minutes. (Current density approximately 20 amps/ftfi.) Shiny bright zinc was deposited on all surfaces including the recesses. The deposit took an excellent chromate conversion coating. Daxad products are made and sold by W. R. Grace Co. of Cambridge, Mass.

EXAMPLE 4 30 g. #6 x /2" steel wood screws were barrel plated in a minibarrel at 2 amps for 20 minutes in the basic bath containing 2.0 g./l. Darvan #1 and 0.4 g./l. 1- allyl, 3-carboxamido pyridinium bromide. A very bright lustrous zinc deposit was obtained. The deposit took both a nitric acid bright dip and a chromate conversion dip without difficulty.

EXAMPLE 5 A 30 g. load of #6 x /2" steel wood screws was barrel plated at 2 amps for 20 minutes in the basic bath containing 1.0 g./l. of a water-soluble condensation product between benzene sulfonic acid and formaldehyde (Darvan #2) and 0.4 g./l. l-allyl, 3-carboxamido pyridinium bromide. A shiny bright product was obtained.

Another 30 g. #6 x V2" steel wood screws were likewise barrel plated in the basic bath containing only 1.0 g./l. Darvan #2. The screws were dull matte gray and of unacceptable commercial quality.

A third 30 g. load of screws was likewise barrel plated in the basic bath containing only 0.4 g./l. l-allyl, 3-carboxam'ido pyridinium bromide. Again the screws were dull gray and of unacceptable commercial quality.

EXAMPLES 6-11 Minibarrel plating tests were conducted on 30 g. loads of screws, plated at 2 amps for 20 minutes, using the basic zinc chloride bath to which had been added 2.0 g./l. Daxad #11. In addition, quaternized pyridines were added in the amounts stated and with the results shown in Table I.

was added as brightener 2.0 g./l. Darvan #1 and 0.8 g./l. l-allyl, 3-car-boxamido pyridinium bromide. 30 g. of screws were barrel plated at 2 amps for 20 minutes in a minibarrel using this bath. As plated they were semibright. After dipping in 0.5 weight percent nitric acid, brightness was improved and they were of acceptable commercial quality.

EXAMPLE 14 A 4-liter basic zinc chloride bath containing 32 g./l. ZnCl and 200 g./l. NH Cl was operated at pH 5.1 for 610 ampere hours of barrel plating electrolysis using a 10 percent by weight aqueous brightener containing 2.5 parts of a. water-soluble condensation product between naphthalene sulfonic acid and formaldehyde and 1 part of l-allyl, 3-carboxamido pyridinium chloride. Average temperature of operation was 20-25" C. and the bath was producing fully bright zinc deposits. Temperature of the bath was raised successively to 30 C., 35 C., C. and C. As the temperature was raised, brightness was lost from the deposit, more particularly the liquid luster. However, work of acceptable commercial quality was obtained, after bright dipping, even at 45 C.

EXAMPLES 15-21 In examples 15 to 21 tabulated below, are recorded the results of 267 ml. Hull Cell tests on various polymerl-allyl, 3-carboxamido pyridinium bromide (ACPB) combinations. The tests were conducted at 2025 C. using the basic chloride bath containing 15 g./l. Zn, Cl/Zn=10/1 and pH 5.1. Electrolysis current was 1.5 amps for 5 minutes.

Amount ACPB Deposit Example Amount polymer (g./i.) (a./it. Appearance 15 4 g./l. Verse-TL" 70 0. 8 0:2 E 16 2g.ll. Verse TL" 400.. 0.8 6 A bright P 0. 4 0-80 Bright with some dull streaks. g ll "Ionac PE-100 0. 8 Brilliant above 6 a./i't.

. "Ionac" PE-llO- 0.8 Brilliant above 15 e../it.

.ll. Ionac PE-120 0.8 Brilliant above 12 a./it.=

./l. J efiamine" ED-600 0. 8 Brilliant above 6 a./1t.

TABLE I Ex. Amount No. Additive (g./l.) Results 6 1-propargyl, 3-carbo- 0. 04 Acceptable commercial rnethoxy pyridinium product after nitric bromide. acid bright dip.

7 l-allyl, 3-cyano 0. 08 Semibright, very nice pyridinium bromide; shiny bright roduct after bright p.

8"-.. l-allyl, 3-iormyl 0. 2 Semibiight. Bright shiny pyridinium bromide. giroduet after bright 9"..- 2-butene 1,4 bis (3- 0. 08 Very bright and shiny carboxamido after bright dip. pyridinium bromide). Brittle deposit.

10.--- 1-(4-ch1orobutene-2) 0. 4 Bright shiny deposit Bearboxamido after bright dip. Dark pyridinium bromide. color.

11.... l-carbomethoxy methyl 2 Shiny bright product S-earboxamido after bright dip. pyridinium bromide.

EXAMPLE 12 EXAMPLE 13 To a zinc sulfate bath containing: ZnSO -7H O Q /l.. 250 (NH SO g /l.. 30 pH 3.8

Versa-TL 70 and Versa-TL 400 are polystyrenesulfonates (sodium salts), average molecular weights 70,- 000 and 400,000 respectively, supplied by National Starch and Chemical Company of Plainfield, NJ.

PVP is polyvinylpyrrolidone, grade K15, average molecular weight 10,000, supplied by GAF Corporation of 140 W. 51st St., New York, N.Y.

Ionac PE-lOO, PEI-110, PE-120 are quaternized condensation products of epihalohydrins and polyamines manufactured and supplied by Ionac Chemical Division of Sybron Corporation of Birmingham, N.J., according to the teachings of US. 3,642,663.

Jeflamine ED-600 is a polyoxyalkylidamine, average molecular weight 600, supplied by I elferson Chemical Corporation of Houston, Tex.

EXAMPLE 22 A -liter bath containing 7.5 g./l. Zn, Cl/Zn weight ratio of 25 1, and pH 6.1 was operated continuously using a 10 wt. percent brightener solution containing 2.5 parts of a water-soluble naphthalene sulfonic acid-formaldehyde condensation product and 1 part of l-allyl, S-carboxamido pyridinium bromide. After an initial 2 1. addition of brightener, miscellaneous work pieces (bolts, nuts, washers, screws, hinges, etc.) were barrel plated so as to deposit about a 0.2 mil thickness of zinc at temperatures of 25C., 35 C., 43 C., and 51 C. No brightness loss was observed in raising temperature from 25 C. to 35 C. Some brightness loss was observed at 43 C. but was restored by adjusting the Cl/Zn ratio to 30/1. Some further loss in brightness was experienced at 51 C. which could not be restored either by brightener or ammonium chloride additions.

What is claimed is:

1. An aqueous addition agent for a zinc electroplating bath comprising an aqueous solution containing (a) about 1 to 25 percent by weight of a pyridinium compound of the general formula:

wherein R is CONH CN, CHO or -COOR"; R is an alkyl group of 14 carbon atoms,

--CH CH=CH -CH CHECH,

R" is an alkyl group of 1-4 carbon atoms; and X- is a halogen ion; and

or naphthalene sulfonic acid groups connected with each other by methylene bridges.

2. The addition agent of Claim 1 wherein the concentration of the pyridinium compound is about 1 to 10 percent by weight and the concentration of said other compound is about 1 to 20 percent by weight.

3. The addition agent of Claim 2 wherein the pyridinium compound is selected from the group consisting of l-allyl, 3-carboxamido pyridinium halide; l-methyl, 3- carboxamido pyridinium halide; l-propargyl, 3-carboxamido pyridinium halide; 1-(4-chlorobutene-2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3-carboxamido pyridinium halide); l-carbomethoxymethyl, 3-carboxamido pyridinium halide; l-propargyl, 3-carbomethoxy pyridinium halide; 1-allyl, 3-cyano pyridinium halide and l-allyl, 3-formyl pyridinium halide, wherein the halogen is chlorine, bromine or iodine; and wherein said other compound is a water-soluble condensation product of a naphthalene sulfonic acid, or a salt thereof, with formaldehyde, said condensation product containing at least 2 naphthalene sulfonic acid groups connected with each other by methylene bridges.

References Cited UNITED STATES PATENTS 3,318,787 5/1967 Rindt et al 204- Y 3,411,996 11/1968 Rushmere 204-55 Y X 3,734,839 5/ 1973 Hoyer et al. 204-55 Y 3,755,097 8/1973 Cope 204-55 Y GERALD L. KAPLAN, Primary Examiner US. Cl. X.R.

204Dig. 2