US3770599A

US3770599A - Acid zinc plating baths

Info

Publication number: US3770599A
Application number: US00146445A
Authority: US
Inventors: S Martin
Original assignee: Oxy Metal Finishing Corp
Current assignee: OMI International Corp; Oxy Metal Industries Corp
Priority date: 1971-05-24
Filing date: 1971-05-24
Publication date: 1973-11-06
Anticipated expiration: 1990-11-06

Abstract

An acid zinc electroplating bath which contains a brightening amount of a soluble thiourea of the formula

D R A W I N G

Description

United States Patent 11 1 Martin [4 1 Nov. 6, 1973 [5 AC) ZINC PLATING BATHS 2,696,467 12 1954 Overcash et al. 204/52 R 2,742,412 4/1956 Cransberg et al..... 204/52 R [751 lnvemor- Mam", Dem)", 2,910,413 10 1959 Strauss et al 204 44 73 Assignee; o Metai Finishing Corporation, 3,502,551 3/1970 Todt et al. 204/52 R warren, Mich 3,558,448 1/1971 Accarles et al. 204/55 R Flledi y 1971 Primary Examiner-F. C. Edmundson [2]] Appl No; 146,445 Attorney-Wm. J. Schramm et al.

[63] ggg sgg z gg of 822941 May An acid zinc electroplating bath which contains a brightening amount of a solublethiourea of the formula [52] 11.8. C1. 204/55 R, 204/D1G. 2 s [51] Int. Cl C23b 5/12 ll [58] Field of Search 204/55, 55 R, 55 Y wherein R is independently selected from the groups References Clled consisting of hydrogen, alkenyl of up to 4 carbon atoms UNITED STATES PATENTS and alkynyl of up to 4 carbon atoms, provided that at 3,655,533 4 1972 Page et a1. 204 55 R least one R is alkenyl or y y The Zinc P g baths 2,080,479 5/1937 Hoff 204455 Y may be either acid sulfate or acid fluoroborate baths 2,828,252 3/1958 Fischer.... 204/55 Y and desirably contain the thiourea compound in an 1,903,860 4/1933 Gockel 0 /55 Y amount of at least about 0.01 grams per liter. 2,563,360 8/1951 Phillips et al. 204/52 R 2 Claims, No Drawings ACID ZINC PLATING BATHS This application is a continuation-in-part of U.S. Ser. No. 822,041 filed May 5, 1969, now abandoned.

This invention relates to improvements in the electrodeposition of zinc and more particularly it relates to improved compositions and processes for the electrodeposition of bright zinc from acid zinc plating baths.

Heretofore, a great deal of the bright zinc electroplating has been carried out using alkaline zinc electroplating baths which contain cyanide. Although such zinc plating baths have generally been satisfactory from the standpoint of the characteristics of the bright zinc electroplate produced, because of the highly toxic nature of the cyanide constituents, the use of such baths has involved considerable problems in the area of waste disposal. These problems have been accentuated recently by the adoption of more stringent laws and regulations on pollution;

Although acid zinc plating baths, instead of those containing cyanide, are not new, the use of such acid plating solutions does present some problems and, hence, these have not been widely adopted. Among the problems involved in using such acid zinc plating solutions is that it is often difficult to obtain a zinc plate having the desired brightness. Additionally, it has been found that even where the desired bright zinc plate is obtained, such plate is often undesirably brittle.

It is, therefore, an object of the present invention to provide an improved acid zinc plating composition for the electrodeposition of a bright zinc plate.

Another object of the present invention is to provide an improved process for bright zinc plating which utilizes an acid zinc plating solution.

A further object of the present invention is to provide an improved zinc plate having a uniform, high degree of brightness, which plate is not undesirably brittle.

These and other objects will become apparent to those skilled in the art from the description of the invention which follows.

Pursuant to the above objects, the present invention.

includes an electroplating bath which comprises an aqueous acidic solution of an inorganic zinc salt, which solution contains a brightening amount of a soluble thiourea material of the formula over a relatively wide range of operating conditions.

More specifically, the plating baths of the present invention are aqueous acidic solutions containing zinc sulfate or zinc fluoroborate, and a brightening amount of one or more soluble thiourea materials. Acid zinc plating baths, whether based on zinc sulfate or on zinc fluoroborate are conventional and known in the art. When based on zinc sulfate, these baths typically contain zinc sulfate in an amount within the range of about 50 to 400 grams per liter. Additionally, such baths may also contain conductive salts to improve the bath conductivity such as ammonium sulfate, ammonium chloride or bromide and the like, which salts are typically present in amounts within the range of about 10 to 30 grams per liter. Additives to control the pH of the bath, such as boric acid, ammonium sulfate, and the like, may also be included, typically in amounts within the range of about 10 to 30 grams per liter. Additionally, additives such as aluminum sulfate, dextrin, licorice, glucose, or the like may also be added, typically in amounts within the range of about 1 to 30 grams per liter, to improve the crystal structure of the zinc plate obtained and provide a wider operating range of current density.

With plating baths based on zinc fluoroborate, the zinc fluoroborate is typically present in amounts within the range of about 50 to 300 grams per liter. Such baths may also contain one or more ammonium salts, such as ammonium chloride, ammonium fluoroborate, and the like, which materials are typically present in amounts within the range of about 10 to 30 grams per liter.

In addition to the above components, the electroplating baths of the present invention also include a brightening amount of at least one soluble thiourea compound. By a soluble thiourea material, it is intended that the materials used have a sufficient solubility in the aqueous acidic plating baths so that a brightening amount of the thirouea material will be dissolved in the bath. In many instances, such brightening amount of the thiourea materials has been found to be at least about 0.01 gram per liter. The maximum amount of the thiourea brightening agent may be up to the limit of its solubility in the aqueous acidic plating bath and will, thus, vary, depending upon the particular thiourea material used. In many instances, it has been found that amounts of thiourea brightener in excess of about 10 grams per liter do not result in any appreciable increase in the brightness of the plate which is obtained. Preferably, the amount of the thiourea brightener in the acid plating bath of the present invention is within the range of about 0.01 to 10 grams per liter.

The soluble thiourea materials used desirably are of the formula:

wherein R is independently selected from the group consisting of hydrogen, alkenyl of up to 4 carbon atoms and alkynyl of up to 4 carbon atoms, provided that at least one R is alkenyl or alkynyl.

It is to be appreciated, that various thiourea materials, as encompassed by the definition set forth hereinabove which are soluble in the plating baths, may be used as brighteners in the electroplating baths of the present invention. Exemplary of specific thiouria materials which may be used are N-allylthiourea; N,N'- ethylenethiourea; N,N-dibutynylthiourea; N,N'- dibutenylthiourea and the like. It is to be appreciated, however, that the above are merely exemplary of the various thiourea materials which may be used as brighteners, and that other similar materials, as fall within the definition set forth hereinabove, may also be utilized to obtain satisfactory results.

The electroplating baths of the present invention may be used over a wide range of operating conditions. Desirably, the bright zinc plate is electrodeposited from the bath using an average cathode current density of from about 10 to amps per square foot, with bath temperatures within the range of about 15 to 40 C. If

desired, during plating the bath may be agitated with air or mechanically, or the work pieces may themselves be mechanically agitated, or plating may be carried out in a non-agitated bath. Preferably, during plating, the bath is maintained at a pH within the range of about 2.7 to 5.8, the desired pH generally being maintained by the addition of a suitable material, such as ammonium hydroxide, zinc carbonate, or the parent acid of the zinc salt in the system.

By the use of the method of the present invention, there is electrodeposited an excellent, bright zinc plate, which plate is not undesirably brittle. Moreover, it is found that this bright zinc plate is produced even in areas of low current density and that in high current density areas, there is little or no evidence of burning of the zinc electroplate deposit. Additionally, it is found that since only relatively small amounts of the thiourea material brighteners are required to produce these results, the use of such materials is quite economical.

In order that those skilled in the art may better understand the present invention and the manner in which it may be practiced, the following specific examples are given. In these examples, unless otherwise indicated, parts and percent are given by weight and temperatures are in degrees Centigrade. It is to be appreciated, however, that these examples are merely exemplary of the present invention and are not to be taken as a limitation thereof.

EXAMPLE 1 An aqueous acid zinc plating bath was formulated containing the following components in the amounts indicated:

Zinc sulfate l80 grams/liter Boric acid 23 grams/liter N-allylthiourea l grams/liter One liter of this bath, at a pH of 4.5 and a temperature of 24 C was air agitated and a bright zinc electroplate was obtained on steel cathodes by electrolyzing the bath at a cathode current density of about 40 ampereslsquare foot, at plating times of from 20 to 40 minutes.

EXAMPLE 2 Into two (60) gallon tanks were added 74 lbs. of ZnSo, 9 lbs. of (Nl-l.,) SO and 10 lbs. or boric acid.

lnto tank A was added 21 grams thiourea while to tank B was added 3.5 grams of N-allyl thiourea. The tanks were filled with water. Zinc was plated for 400 amp hours/gal. of solution taking from two to three months to complete. During the electroplating, replenishment solution was added hourly. To tank A" was added 435 mg/hr. of thiourea while to tank 8" was added 76 mg/hr. of N-allyl thiourea. At the end of the experiment, the amount of thiourea used was calculated at 12.5 mg/amp hour of plating time while N-allyl thiourea used only 2.09 mg/amp hour of plating time.

The results of the above described experiments clearly shown that an unsaturated thiourea, especially, N-allyl thiourea is surprisingly more stable than thiourea.

While there have been described various embodiments of the invention, the compositions and methods described are not intended to be understood as limiting the scope of the invention as changes therewithin are possible and it is intended that each element recited in any of the following claims is to be understood as referring to all equivalent elements for accomplishing substantially the same results in substantially the same or equivalent manner, it being intended to cover the invention broadly in whatever form its principle may be utilized.

What is claimed is:

1. An electroplating bath, which comprises an aqueous acidic solution having present therein 50 to 400 grams of zinc sulfate per liter or 50 to 300 grams of zinc fluoroborate per liter; 0.01 to 10 grams per liter of a soluble thiourea brightening material selected from the group consisting of N-allylthiourea; N,N- ethylenethiourea; N,N'-dibutynylthiourea; and N,N' dibutenylthiourea; 10 to 30 grams per liter of an ammonium salt selected from the group consisting of ammonium sulfate, ammonium chloride and ammonium bromide to improve the conductivity of the bath; 10 to 30 grams per liter of boric acid or ammonium sulfate to maintain the pH of the bath during plating within the range of about 2.7 to 5.8; and l to 30 grams per liter of a material selected from the group consisting of aluminum sulfate, dextrin, licorice and glucose to improve the crystalline structure of the zinc plate obtained and to provide a wider operating range of current density.

2. A method for the electrodeposition of a bright zinc plate which comprises electrodepositing zinc at an average cathode current density of from about 10 to amps per square foot and the bath temperature within the range of about 15 to 40 C from the aqueous acid zinc electroplating bath of claim 1.

Claims

2. A method for the electrodeposition of a bright zinc plate which comprises electrodepositing zinc at an average cathode current density of from about 10 to 120 amps per square foot and the bath temperature within the range of about 15 to 40* C from the aqueous acid zinc electroplating bath of claim 1.