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
  • C25D3/56—Electroplating: Baths therefor from solutions of alloys
  • C25D3/565—Electroplating: Baths therefor from solutions of alloys containing more than 50% by weight of zinc

Definitions

• the present invention relates generally to improvements in the electrodeposition of zinc nickel alloys from aqueous alkaline plating baths and to new additives for use in such electrodeposition processes.
• Electrodeposition of zinc and zinc alloys based on alkaline plating baths has been known for many years. However, it is not possible to produce a commercially acceptable deposit from a simple sodium zincate electrolyte as the deposit is powdery and dendritic. For this reason, various additives have been proposed to provide improved deposition, such as cyanides (which have obvious environmental problems) and polymers of amines and epichlorohydrin which act as grain refining additives. These polymers are limited to usage in baths having relatively low concentrations of zinc because it is not possible to prevent uncontrolled deposition of zinc at higher metal concentrations.
• additives have been proposed which allow higher zinc concentrations to be used, which have significantly reduced burning and pitting and which allow a wider range of operating parameters. Further, the additives enable an excellent deposit distribution (that is, evenness of the deposit across the article being plated, irrespective of its shape in particular areas). This maximizes the efficiency of zinc usage.
• These additives are based generally on polyquaternary amine compounds and are described in U.S. Pat. No. 5,435,898 and U.S. Pat. No. 5,405,523, which also provide further discussion of the prior art and the content each of which is herein incorporated by reference.
• Plating compositions for depositing zinc nickel alloys from alkaline electrolytes are well known and are described in US patents such as US Pat. No. 6,468,411, US Pat. No. 5,417,840, US. Pat. No. 4,861,442, and US. Pat. No. 4,889,602, which also provide further discussion of the prior art and the content each of which is herein incorporated by reference.
• Plating solutions that provide an alloy composition containing from 12% to 15% nickel are most desirable giving optimal corrosion performance. This alloy is currently utilized by many automotive manufacturers.
• the zinc to nickel metal concentration ratio of alkaline zinc nickel plating baths of the prior art producing zinc nickel alloys of >12% Ni containing oligomeric or polymeric amine species is of the order 7:1 to 10:1. This is consistent with the ratio of nickel in the desired alloy of 12% to 15% and corresponds to more 'normal deposition.' Unexpectedly it has been found that baths of the present invention producing zinc nickel alloys of 12% to 15% Ni have a zinc to nickel metal concentration ratio of the order 1.5:1 to 2.5:1. Thus the zinc to nickel metal concentration ratio is not consistent with the alloy deposited.
• This type of deposition is described as 'anomalous deposition' and is generally typical of the acid zinc nickel based electrolytes described in US patents and applications such as US 4,699,696 and US 2003/0085130 Al.
• an object of the present invention to provide an alkaline zinc nickel alloy electroplating bath in which electroplated coatings with even brightness, improved deposit distribution thickness, good resistance to burning, and high cathode efficiency may be obtained in a wide range of current density even in the presence of polluting anions such as carbonate and sulfate.
• Another object of the present invention is to provide an alkaline zinc nickel alloy electroplating bath which may contain a wide range of zinc concentration levels for different plating operations.
• the zinc nickel plating bath be operable in manual, automatic rack and barrel plating operations.
• the present invention is thus concerned with electrodeposition on a variety of electrically conducting substrates in a medium which seeks to provide improved cathode efficiency and/or improved brightness and leveling, and further to provide coatings that are resistant to post-plate "blistering".
• Suitable substrates include iron and ferrous-based substrates (including both iron alloys and steels), aluminum and its alloys, magnesium and its alloys, copper and its alloys, nickel and its alloys, and zinc and its alloys.
• Aluminum and its alloys and ferrous-based substrates are particularly preferred substrates, with steels being most preferred.
• an additive for an alkaline zinc nickel alloy electroplating bath medium comprising a urylene quarternary ammonium based polymer. It has been discovered that a zinc nickel alloy electroplating bath containing an effective additive amount of a urylene quarternary ammonium based polymer accomplishes the objects of the present invention when used in conjunction with non-polymeric complexants.
• a polymer that is preferred by the present invention because of its effectiveness in enabling the plating bath to plate over a wide range of current densities is Urea, N,N'-bis[3-(dimethylamino)propyI]-, polymer with l,l '-oxybis[2-chloroethane].
• Urea N,N'-bis[3- (dimethylamino)propyl]-, polymer with 1,4-dichlorobutane.
• Others include random copolymers comprising the reaction product of (i) one or more di-tertiary amines, including an amide or thioamide functional group and (ii) one or more second di-tertiary amines including an unsaturated moiety with (iii) one or more first linking agents capable of reacting with said amines (i) and (ii).
• Such useful random co-polymers are disclosed in U.S. Patent No. 7,109,375, the teaching of which are incorporated herein in their entirety.
• the polymers useful in this invention include at least one urea based polymer of the form of either (a) Urea, N, N'-bis[3-at (dialkylamino) alkyl]-, polymer with 1,4 [2-haloaklane] or (b) Urea, N,N'-bis[3-(dialkylamino)alkyl], polymer with 1,1'- oxybis[2-haloalkane], wherein for (a) or (b) the alkyl functional groups are selected from the group consisting of methyl, ethyl, proply, butyl, pentyl, and hexyl and the halogen functional group is selected from the group consisting of chloro, bromo, fluoro, and iod
• non-polymeric complexants that are preferred by the present invention include trimethanolamine, triethanolamine, tripropanolamine, or N,N,N',N' tetrekis- hydroxyisopropylethylenediamine. It is also preferable that at least two of these complexants are concurrently used in the bath.
• the improved baths exhibit many advantages over the baths of the prior art, including even deposit appearance, effective plating at a high current density, uniform plating thickness, and high cathode efficiency. It is particularly advantageous that the improvements of the present invention result in uniform plating thickness because it is a well known deficiency in the prior art that uniform plating thickness is difficult when the objects being plated comprise complex shapes with small ridges and surface variations. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
• polycationic polymers in zinc plating solutions is well known and has been utilized in zinc plating systems for many years. These polymers are generally able to produce processes that yield metal plating that is resistant to burning and pitting and exhibit a highly uniform metal distribution. Polycationic polymers are also used in the deposition of zinc iron and zinc cobalt deposits where the complexant used to hold the iron or cobalt in solution is typically sodium heptonate, sodium gluconate, or sodium tartarate. Examples of such baths that are able to plate both zinc and zinc alloys are disclosed in U.S. Pat. No. 4,983,263 to Yasuda et al, the content of which is herein incorporated by reference.
• polycationic polymers have not been thought to be effective in zinc nickel plating electrolytes. It is desirable and widely sought throughout the plating industry to produce deposits of zinc nickel alloy containing 12% to 15% nickel. These processes generally suffer from several problems including non-optimal plating uniformity and low brightness and cathode efficiency. It has been discovered that the combination of certain amino based complexants and urea based polycationic polymers, rather than the usual oligomeric or polymeric amine complexants and epichlorohydrin based polycationic polymers, greatly improves the quality of zinc nickel electroplated deposits.
• This improved process gives similar metal thickness distribution characteristics to zinc plating but which can contain the desirable features of a zinc nickel alloy.
• a similar resistance to burning or pitting between the zinc and zinc nickel processes is also observed even in the presence of interfering anions such as carbonate and sulfate.
• the final result is that a zinc nickel process utilizing the additives of this invention can be operated to produce zinc nickel alloys containing 12% to 15% nickel still retaining the good deposition characteristics and extended operable current density range which was heretofore only achievable with a pure zinc plate.
• Alkaline zinc electroplating baths both containing cyanide ions and cyanide free baths, are well known in the art and have been commonly used for years.
• the basic alkaline zinc electroplating bath contains a zinc compound and an alkali hydroxide.
• Zinc can be introduced into the aqueous bath by any soluble zinc salt, but zinc oxide is the salt most often and most preferably used.
• the alkali hydroxide is generally either sodium hydroxide or potassium hydroxide.
• the zinc ions from the zinc salt are transformed into a zincate ion, and thus zincate ions are generally present in a working alkaline zinc plating bath.
• the term "zinc ion” includes zincate or other ionic species containing zinc atoms useful in electroplating baths for electroplating metallic zinc and zinc alloys.
• Zinc alloy electrolytic baths also contain salts of other metals, which are generally nickel, cobalt, or iron.
• the present invention deals specifically and most preferably with zinc nickel alloy plating. Nickel is introduced into the zinc plating bath by means of any soluble nickel salt. It is most preferable if this salt contains divalent nickel, and therefore the most common and preferable nickel salts for use in the present invention are nickel (II) sulfate or nickel (II) acetate or nickel (II) carbonate.
• the composition of the zinc nickel plating bath generally contains about 5-25 g/L, but can contain up to 50 g/L or more, of zinc ions. This content is calculated on zinc ion concentration and would not be affected by whatever corresponding anion (or cation) is used.
• zinc is present in the solution at a concentration of about 5-20 g/L.
• the alkaline hydroxide preferably sodium or potassium hydroxide, is generally present at a concentration of about 50 g/L to 500 g/L or more, and is preferably about 70 to 100 g/L as sodium hydroxide or 100 to 140g/l as potassium hydroxide.
• Nickel is generally present in such baths from about 0.25 -10 g/L, but is preferably in the range of 1-6 g/L.
• the zinc nickel bath can be used in widely different concentration ranges.
• the desirable zinc concentration is about 5 to 10 g/L, preferably 6 to 8 g/1 and about 70 to 140 g/I for the alkali hydroxide.
• the desired concentration of zinc is about 8 to 12 g/1 and 80 to 150 g/1 alkali hydroxide.
• a chelating agent in the bath in an effective amount to maintain the metals, other than the soluble zinc, in the bath in solution, e.g., to dissolve the required amount of nickel and other alloy ingredients in the bath.
• the chelating agent used herein should complex the nickel ions to an electrodepositable extent in a strong alkalinity of a pH of above 13 and thus permit their stable dissolution. It is an essential aspect of the present invention that appropriate complexants be used to effectively dissolve the nickel ions into solution.
• the preferred chelating agents are selected from the group consisting of monoethanolamine, diethanolamine, trimethanolamine, triethanolamine, tripropanolamine, and N,N,N',N' tetrakis-hydroxyisopropylethylenediamine.
• the functionality of the present invention can be achieved with any amino alcohol or ethylenediamine based complexing agent provided that it is not polymeric.
• the chelating agent should generally only be present in the plating solution at a concentration high enough to ensure the dissolution of the nickel ions. Generally, levels of about 10-150 g/L or more are employed and depend upon the concentration of nickel or other alloying metal in a given bath.
• the second essential aspect of the present invention is the use of particular polycationic polymers which aid in the plating process to produce a better quality zinc nickel alloy plate. The incorporation of these materials gives the process a very high throwing power, which results in a uniform metal distribution, as well as aiding in producing plates that are resistant to burning and pitting.
• polymers that are able to exhibit such a result are urylene quaternary ammonium based polymers, which include as polymers of the form Urea, N,N'-bis[3-(dialkylamino)alkyl]-, polymer with l,4-[2-haloalkane] or Urea, N,N'-bis[3-(dialkylamino)alkyl]-, polymer with l,l '-oxybis[2- haloalkane] or Urea, N,N'-bis[3-(dimethylamino)propyyl)]-, polymer with 1,4- dichlorobutane.
• polymers useful in this invention include random co-polymers comprising the reaction product of (i) one or more di-tertiary amines, including an amide or thioamide functional group and (ii) one or more second di-tertiary amines including an unsaturated moiety, with (iii) one or more first linking agents capable or reacting with said amines (i) and (ii).
• random co-polymers are disclosed in U.S. Patent No. 7,109,375, the teachings of which are incorporated herein by reference in their entirety.
• a polymer that is preferred by the present invention because of its effectiveness in enabling the plating bath to plate over a wide range of current densities is Urea, N,N'-bis[3- (dimethylamino)propyl]-, polymer with l,l'-oxybis[2-chloroethane].
• Urea N,N'-bis[3-(dimethylamino)propyl]- 3 polymer with 1,4- dichlorobutane and others such as Urea, N,N'-bis[3-(dimethylamino)propyl)]-, polymer with 1,4-dichlorobutane and N'-[3-(dimethylamino)propyl]-N,N'-dimethyl-l,3- propanediamine, N-[2-hydroxy-3-(2-propenyloxy)propyl) derivatives.
• the urea based polymer is preferably present in an amount of up to about 20 g/L, more preferably 0.01 g/L to 7g/L, and most preferably at a concentration of about 0.1-2g/L.
• the zinc nickel alloy electroplating bath of the present invention can be utilized to obtain uniform coatings over a wide range of current densities, which are additionally resistant to burning and pitting. These results are obtainable even if the concentrations of the components change to a reasonable degree. It is the ability to effect a uniformly thick coating of zinc-nickel alloy under different current density that forms one of the primary advantage of the present invention.
• Example 1 An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 90 g/L sodium hydroxide, 8g/L zinc ions, 4g/l nickel ions, 68g/L triethanolamine, 30g/L N,N,N',N' tetrakis-hydroxyisopropylethylenediamine, 12.5g/l sodium silicate, and 400mg/L Urea, N,N'-bis[3-(dimethylamino)propyl]-, polymer with l,l'-oxybis[2-chloroethane].
• a bright steel Hull cell panel was plated for 20 minutes at IA in a Hull cell using a nickel anode.
• the plated panel appearance was uniformly bright with no visible defects.
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4A, 2A, 0.5A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B.
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 90 g/L sodium hydroxide, 8g/L zinc ions, 4g/l nickel ions, 68g/L triethanolamine, 30g/L N,N,N',N' tetrakis-hydroxyisopropylethylenediamine, 12.5g/l sodium silicate, and 100mg/L Urea, N,N'-bis[3-(dimethylamino)propyi)]-, polymer with 1,4-dichlorobutane and N'-[3-(dimethylamino)propyl]-N,N'-dimethyl- 1,3- propanediamine, N-[2-hydroxy-3-(2-propenyloxy)propyl) derivatives.
• a bright steel Hull cell panel was plated for 30 minutes at IA in a Hull cell using a nickel anode.
• the plated panel appearance was uniformly bright with no visible defects.
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4A 5 2A, 0.5A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B.
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 120 g/L potassium hydroxide, 8g/L zinc ions, 4g/I nickel ions, 68g/L triethanolamine, 30g/L N,N,N',N' tetrakis-hydroxyisopropylethylened ⁇ amine, 12.5g/l sodium silicate, and 100mg/L Urea, N,N'-bis[3-(dirnethylamino)propyl)]-, polymer with 1,4-dichlorobutane and N'-[3-(dimethylamino)propyl]-N,N'-dimethyl-l,3- propanediamine, N-[2-hydroxy-3-(2 ⁇ propenyloxy)propyl) derivatives.
• a bright steel Hull cell panel was plated for 30 minutes at IA in a Hull cell using a nickel anode.
• the plated panel appearance was uniformly bright with no visible defects.
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4A, 2A, 0.5A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B. (Example 4)
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 90 g/L sodium hydroxide, 12g/L zinc ions, 4.5g/l nickel ions, 60g/L triethanolamine, 12.5g/l sodium silicate, and 400mg/L Urea, N,N'-bis[3-
• Fischerscope X-ray system XDL-B Fischerscope X-ray system XDL-B.
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 110 g/L sodium hydroxide, 8g/L zinc ions, 700mg/l nickel ions, 8g/L tetraethylenepentamine, 2g/l triethanolamine, 15g/L N,N,N',N' tetrakis- hydroxyisopropylethylenediamine, 4g/l sodium silicate and 50mg/L N-benzyl nicotinamide .
• a bright steel Hull cell panel was plated for 20 minutes at IA in a Hull cell using a nickel anode.
• the plated panel appearance was uniformly bright from the low led to 4asd and beyond 4asd was dull showing a coarse grained deposit .
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4A, 2A 5 0.5A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B,
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 1 10 g/L sodium hydroxide, 8g/L zinc ions, 700mg/l nickel ions, 8g/L tetraethylenepentamine, 2g/I triethanolamine, 15g/L N,N,N',N' tetrakis- hydroxyisopropylethylenediamine, 4g/I sodium silicate, 400mg/L Urea, N,N'-bis[3- (dimethylamino)propyl]-, polymer with l,l '-oxybis[2-chloroethane] and 50mg/L N- benzyl nicotinamide .
• a bright steel Hull cell panel was plated for 20 minutes at IA in a Hull cell using a nickel anode.
• the plated panel appearance was uniformly bright with no visible defects.
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4A, 2A, 0.5A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B.
• An aqueous electrolytic bath suitable for plating zinc nickel alloy was prepared containing 90 g/L sodium hydroxide, 8g/L zinc ions, 4g/I nickel ions, 68g/L triethanolamine, 30g/L N,N,N',N' tetrakis-hydroxyisopropylethylenediamine and 12.5g/l sodium silicate.
• a temperature 3OC a bright steel Hull cell panel was plated for 20 minutes at IA in a Hull cell using a nickel anode. The plated panel appearance showed three distinct bands.
• the first band from the HCD region beyond 5asd showed a coarse grained deposit
• the second band from 5asd down to about 0.5asd was semi bright to dull
• the third band below 0.5asd was bright.
• the deposit thickness and nickel alloy content shown in Table 1 below was measured at current densities 4 A, 2A, 0.5 A per square decimeter across the plated panel using a Fischerscope X-ray system XDL-B.
• Example 5 is a bath containing the oligomeric based amine complexant tetraethylenepentamine and Example 6 is the same bath as Example 5 with a polycationic polymer.

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