Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D3/00—Electroplating: Baths therefor
  • C25D3/02—Electroplating: Baths therefor from solutions
  • C25D3/22—Electroplating: Baths therefor from solutions of zinc

Definitions

• R is CONH,, -CN, CHO or COOR;
• This invention relates to acid zinc electroplating baths and processes, and additives useful therein, and, more particularly, to such baths and processes for depositing bright zinc plates.
• Quaternary pyridine compound additives useful in alkaline cyanide zinc plating are described in U.S. Pat. No. 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 U.S. Pat. No. 3,411,996, issued to John D. Rushmere on Nov. 19, 1968.
• an aqueous acid zinc electroplating bath comprising an aqueous solution of zinc ions, said solution maintained at a pH in the range of about 3.5 and 7.5 and having dissolved therein in an amount effective to give a bright zinc deposit, (a) a pyridinium compound of the general formula:
• a is -coNH,, -CN, CHO or COOR";
• a water-soluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof, with formaldehyde said condensation product containing at least 2 benzene or naphthalene sulfonic acid groups connected with each other by methylene bridges.
• an aqueous addition agent for a zinc electroplating bath consisting essentially of an aqueous solution with about 1 to 25 percent by weight of the above-described pyridinium compound and about 1 to 50 percent by weight of the above-described condensation product.
• This invention pertains to the electrodeposition of zinc from acid 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 hydroxide or other bases, or an acid as required.
• bath pH will generally be at a slightly acidic pH between 3.5 and 6
• a higher pH bath such as to pH 7.5
• a base such as ammonium hydroxide
• ammonium chloride is added to improve electrical conductivity.
• the bath will have a chloride ion to zinc ion weight ratio in the range from 4/1 to 16/ l preferably from 6/1 to 12/ 1.
• Zinc metal content in the zinc chloride bath, as well as the other acid 'zinc baths, will range from about 6 to 45 grams per liter, preferably about 6 to 20 grams per liter.
• Bath formulations may contain mixtures of zinc salts such as the use of both 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 of acceptable commercial quality can be obtained from a bath operated at a temperature 'in the range of about 10 to 45C. Normally, the bath is operated at about 20 to 30C.
• Zinc deposits obtained from such acid baths 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 and water-soluble condensation products of an aryl sulfonic acid with formaldehyde is added to the acid z'inc 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:
• R" is an alkyl group of one to four carbon atoms
• R is CONH -CN, Cl-l or COOR
• X is a halogen selected from fluorine, chlorine and bromine.
• the pyridinium compound is used at a concentration level of about 0.02 to 20 grams per liter, preferably about 0.05 to grams per liter.
• Preferred pyridinium compounds are l-allyl, 3- carbox-amido 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 watersoluble 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. No. 3,537,959.
• the condensation product is added in an amount to give a bath concentration of about 0.5 to 50 grams per liter, preferably about t 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 percent, of the pyridinium compound and about i 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).
• EXAMPLE 1 A steel Hull Cell panel was plated at 2 amps for 5 minutes in the basic bath containing 2.0 g./l. of a waters'oluble condensation product between naphthalene sulfonic acid and formaldehyde (Darvan No. 1) and 0.8 g./l. l-methyl, 3-carboxamido pyridinium bromide. Bright plate was obtained over the current density range 8-80 amps/ft. Some pitting of the deposit occurred.
• EXAMPLE 2 A steel Hull Cell panel was plated at 2 amps for 5 minutes in the basic bath containing 2.0 g./l. Darvan No. l and 2.0 g./l. l-propargyl, 3-carboxamido pyridinium bromide. Very bright plate free of pits was obtained over the current density range 2-60 amps/ft.
• EXAMPLE 3 EXAMPLE 4 30 g. No. 6 X 7% inch 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 No. l and 0.4 g./l. l-allyl, 3-car boxamido pyridinium bromide. A very bright lustrous zinc deposit was obtained. The deposit took both a nitric acid bright dip and a chromate con version dip without difficulty.
• EXAMPLE 5 A 30 g. load of No. 6 X 12 inch 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 formalde- EXAMPLES 6-1 1 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 No. ll. In addition, quaternized pyridines were added in the amounts stated and with the results shown in Table l.
• EXAMPLE 14 A 4-liter basic basic zinc chloride bath was operated for 610 ampere hours of barrel plating electrolysis using a 10 percent by weight aqueous brightener containing 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 20-25C. and the bath was producing fully bright zinc deposits. Temperature of the bath was raised successively to C., C., C. and C. As the temperature was raised, some brightness was lost from the deposit, more particularly the liquid luster. However, work of acceptable commercial quality was obtained, after bright dipping, even at 45C.
• An aqueous acid zinc electroplating bath comprising an aqueous solution of zinc ions, said solution maintained at a pH in the range of about 3.5 to 7.5, and having dissolved therein in an amount effective to give a bright zinc'deposit, (a) a pyridinium compound of the general formula:
• R" is an alkyl group of one to four carbon atoms
• X is a halogen selected from iodine, chlorine and bromine; and b. a water-soluble condensation product of a benzene or naphthalene sulfonic acid, or salt thereof, with formaldehyde, said condensation product containing at least 2 benzene or naphthalene sulfonic acid groups connected with each other by methylene bridges.
• the pyridinium compound is selected from the group consisting of l-allyl, 3-carboxamido pyridinium halide; 1- methyl, 3-carboxamido pyridinium halide; l-propargyl, 3-carboxamido pyridinium halide; l-(4-chlorobutene- 2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3-carboxami'clo pyridinium halide); l-carbomethoxymethyl, 3-carboxamido pyridinium halide; lpropargyl, Zi-carbomethoxy pyridinium halide; l-allyl, 3-cyano pyridinium halide and l-allyl, 3-formyl pyridinium halide.
• the acid electroplating bath of claim 4 wherein the pyridinium compound is present in an amount in the range of about 0.05 to 5 grams per liter and the condensation product is present in an amount in the range of about 1 to 20 grams per liter.
• The'acid electroplating bath of claim 5 wherein the pyridinium compound is l-allyl 3-carboxamido pyridinium halide and the sulfonic acid used in the condensationproduct is naphthalene sulfonic acid.
• the acid electroplating bath of claim 4 wherein the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 4 0 grams per liter and having a chloride ion to zinc ion carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and (b) about 1 to 20 grams per liter of a water-soluble condensation product of a naphthalene sulfonic acid with formaldehyde, said condensation product containing at least two naphthalene sulfonic acid groups connected with each other by methylene bridges.
• the bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 4 0 grams per liter and having a chloride ion to zinc ion carboxamido pyridinium halide wherein the halide is chloride, bromide or iodide, and
• R is an alkyl group of one to four carbon atoms, 1
• R" is an alkyl group of one to four carbon atoms;
• R is CONH -CN, CHO or COOR";
• X is a halogen selected from iodine, chlorine and brorange of about 0.02 to 20 grams per liter and the condensation product is added to give a bath concentration in the range of about 0.5 to 50 grams per liter.
• the pyridinium compound is selected from the group consisting of lallyl, 3-carboxamido pyridinium halide; l-methyl, 3- carboxamido pyridinium halide; l-propargyl, 3- carboxamido pyridinium'halide; l-(4-chlorobutene-2), 3-carboxamido pyridinium halide; 2-butene 1,4 bis (3- carboxamido pyridinium halide); l-carbomethoxymethyl, 3-carboxamido pyridinium halide; lpropargyl, 3-carbomethoxy pyridinium halide; l-allyl, S-cyano pyridinium halide and l-allyl, 3-formyl pyridinium halide.
• bath is an aqueous acid zinc chloride bath having zinc ions at a concentration in the range of about 6 to 45 grams per liter and having a chloride ion to zinc ion weight ratio in the range of about 4/ 1 to 16/1.

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• Chemical & Material Sciences (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
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• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)

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• 1972
  • 1972-05-23 US US00256179A patent/US3769184A/en not_active Expired - Lifetime
• 1973
  • 1973-05-18 BE BE131277A patent/BE799734A/xx unknown
  • 1973-05-22 FR FR7318522A patent/FR2185692B1/fr not_active Expired
  • 1973-05-22 IT IT24423/73A patent/IT987816B/it active
  • 1973-05-23 DE DE2326300A patent/DE2326300A1/de active Pending
  • 1973-05-23 JP JP48057659A patent/JPS4942531A/ja active Pending
  • 1973-05-23 NL NL7307195A patent/NL7307195A/xx unknown

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