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

• references Cited which comprises an aqueous alkaline substantially UNITED STATES PATENTS cyanide-free solution having dissolved therein at least 733,028 7/1903 Goldberg 204/55 R one sluble Zinc capable of being Plated by 2,451,426 10/1948 Bair at a].
• Some cyanide-free or substantially cyanide-free zinc plating baths are in existence today, and most of these baths appear to be based on a solution of sodium zincate with excess sodium hydroxide.
• High pH alkali zincate baths when used without brightening or addition agents yield deposits that are dull, spongy and of poor appearance. It has been proposed to overcome these deficiencies by adding glycolates to increase smoothness of deposits but commercially acceptable bright plates were not obtainable. It has also been proposed to add, to the high pH zincate baths, alkanolamines either alone or in conjunction with aldehydes to brighten the deposit as in US. Pat. No. 3,317,412.
• Epichlorohydrin-amine reaction products have previously been disclosed as being useful in aqueous zinc cyanide electroplating baths.
• these epichlorohydrinprimary amine reaction products have been used in zinc cyanide baths, they are not good enough to meet todays standards with respect to throwing power, current density and brightness in cyanide free or substantially cyanide free baths.
• the Burnson US. Pat. No. 3,227,638 discloses the use of a cyclic amine, namely, hexamethylenetetramine reacted with epichlorohydrin, again in cyanide electroplating baths.
• the use of this reaction product in conventional zinc cyanide baths, low cyanide baths (about 2 oz./gal.) or even in cyanide-free baths results in insufficient or poor stability of the bath which is unacceptable to meet todays standards.
• large amounts of secondary brighteners are used in low cyanide baths to obtain an acceptable brightness.
• the present invention provides a cyanide free or substantially cyanide free zinc plating bath which is capable of being used in the electrolytic deposition of zinc having a brightness and throwing power equivalent or better than that which can be obtained from commercial cyanide zinc plating baths.
• the plating baths and process of this invention involve the addition of at least one soluble zinc compound capable of being plated by electrolytic deposition and an effective amount of at least one substituted pyridine or quinoline compound possessing at least one amine containing substituent.
• the alkaline soluble zinc salts which can be used in the plating baths according to this invention can be of any zinc compound soluble in an alkaline medium capable of being plated by electrolytic deposition.
• Examples of such zinc compounds and salts are well known in the art and include, for example, zinc sulfate, zinc acetate, and zinc oxide.
• Other alkaline soluble zinc compounds can of course be used, as will be apparent to those skilled in the art.
• the amount of zinc metal in the bath is not critical and can be varied, as known in the art, with respect to other known zinc plating baths.
• the zinc metal content of the baths of this invention is between about one to four ounces per gallon.
• the zinc metal content can be supplied to the bath by means of a conventional soluble zinc anode or by the use of an insoluble anode and by direct addition of the appropriate alkaline soluble zinc compound to the plating solution.
• the alkalinity can be supplied to the aqueous baths by any alkaline material so long as it is capable of dissolving the zinc compound used in the aqueous bath to the desired extent.
• any alkaline material so long as it is capable of dissolving the zinc compound used in the aqueous bath to the desired extent.
• sodium hydroxide and potassium hydroxide can be used to supply the alkalinity.
• Sodium hydroxide is preferable, however, since sodium hydroxide has better solubility with respect to alkali zincates.
• the amount of alkaline compound, such as sodium hydroxide, should advantageously be in excess of that required to form the sodium zincate.
• the amount of excess or free sodium hydroxide is not critical, so long as it is sufficient to keep all the zinc in solution and prevent any precipitation of the zinc from taking place.
• the pH of the electrolyte solutions according to this invention can of course be varied to obtain optimum results as will be apparent to those skilled in the art.
• the pH of the electrolyte solutions of this invention are, however, advantageously maintained at 12 and above.
• substituted pyridine and quinoline compounds which are useful herein must possess at least one amine containing substituent.
• alkyl sultone which has been found to provide good results when reacted with the pyridines and quinolines of this invention is propane sultone.
• Other alkyl sultones can be advantageously employed as will be readily appreciated by one skilled in the art.
• Beta-propriolactone is illustrative of an alkyl lactone which can be reacted with compounds (I) and (II) herein and numerous other lactones can be similarly employed.
• Examples of some epoxides that can be reacted with pyridines (I) and quinolines (II) include ethylene oxide, propylene oxide, epichlorohydrin, allyl glycidyl ether, 2,3-epoxybutane, di-( 1,2-dimethyl-1 ,2- epoxypropyl) ether and a,B-epoxypropionic acid.
• the pyridines (I) and quinolines (II) can be quaternized with numerous known and conventional quaternizing agents such as benzyl chloride, methyl chloride, dimethylsulfate and allyl chloride.
• the amount of pyridine and quinoline compounds of this invention or their epichlorohydrin reaction products can be varied quite widely as will be apparent to those skilled in the art. Generally, the effect of increasing the current density range while maintaining brightness of the Zinc deposits can be noticed with as little as 0.01 grams per liter of the pyridine compounds and their reaction products, In most cases it is advantageous to use about 0.1 to 1 grams per liter although much higher concentrations can be employed up to grams per liter or even higher. Generally, a bright zinc coating is obtained over the full current density range before the concentration reaches 1 gram per liter, and the addition of higher amounts of the pyridine compounds does not result in any more or significant improvements.
• the amount of the pyridine or quinoline compounds used will not only depend upon the particular pyridine or quinoline compound employed, but the current density range desired for plating bright zinc as will be apparent to those skilled in the art. If one does not desire to plate at very high current densities then lesser amounts of the pyridine can be used.
• the aminopyridine-epihalohydrin reaction products can be obtained by merely heating the aminopyridine with epichlorohydrin.
• the particular Z-aminopyridine (formula I) used in the Examples set forth below was prepared by mixing 28 moles of 2-aminopyridine in five gallons of water and slowly adding 49.1 moles of epichlorohydrin to prevent the temperature from rising too rapidly or too high. It is preferred to keep the temperature during this phase of the reaction from rising above about 90C.
• the reaction mixture is then maintained at between about 75 to 80C for about 45 minutes and cooled.
• the finished product has a volume of approximately seven gallons. It is this diluted product containing approximately 27% solids that is used in the examples below and the amounts recited in the Examples are of a 27% solution.
• polyelectrolytes or amine-epihalohydrin reaction products useful as additives according to this in-;
• vention for producing bright zinc platings from cyanide-free or substantially cyanide-free electrolytes are water-soluble polycondensates, of ammonia or an alkylene amine, and an epihalohydrin.
• the polycondensates are in the form of a polymer containing repeating amine groups and have a molecular weight above about 250.
• the water soluble epihalohydrin-alkylene amine polycondensates can be prepared by direct reaction of an epihalohydrin with straight or branched chain alkyl amines or ammonia.
• amine or alkyl amine includes ammonia as used herein with respect to the description of the alkylene amine polycondensates.
• the epihalohydrin-alkylene amine polycondensates that can be used according to this invention can contain recurring amine groups-primary, secondary, tertiary or quaternary.
• the epihalohydrin-alkylene amine polycondensates containing predominantly recurring primary or secondary amines can be produced in accordance with the disclosure of the Winters U.S. Pat. No. 2,791,554 by reacting epichlorohydrin with primary amines or ammonia as described therein.
• ammonia epichlorohydrin reaction product can be produced as in the example in Winters patent beginning at line 68, column 2 and an ethylene diamineepihalohydrin reaction product can be produced in the same manner by substituting the equivalent amount of ethylene diamine for the ammonia in the amount specified at lines 49-55 of Column 3 of the Winters patent, for example.
• Lower alkyl amines are advantageous for reaction with the epihalohydrin and some examples of amines that can be used according to this invention include ethylene diamine, trimethyl amine, triethanolamine, dimethyl amino propylamine, diethyl amino propylamine, n-n' dimethyl amine ethylamine, n-n' dimethyl n methyl propylene diamine, and so forth.
• the methyl, ethyl and propyl groups can be interchanged in various manners in the above mentioned amines.
• polycondensates containing recurring primary, secondary and/or tertiary amines are quite advantageous when used in cyanide free or low cyanide zincate baths, the polycondensates containing quaternary amine groups are particularly advantageous.
• the amine group can be quaternized by known processes using known quaternizing agents, such as methyl chloride, methyl sulfate, allyl chloride, benzyl chloride, butene chloride, hexyl chloride and propargyl chloride.
• known quaternizing agents such as methyl chloride, methyl sulfate, allyl chloride, benzyl chloride, butene chloride, hexyl chloride and propargyl chloride.
• the polycondensates of this invention containing repeating tertiary or quaternary amine groups can be prepared using primary amines or mono amines in the initial reaction with an epihalohydrin and the resulting polymer further reacted to form the recurring tertiary and/or quaternary amine groups such as by subjecting the polymer to a quaternization reaction as set forth in Procedure ll below.
• a quaternization reaction as set forth in Procedure ll below.
• the products of the Winters patent as described above could be converted into polymers containing recurrig tertiary and/or quaternary groups by subjecting the polymer to a quaternization reaction as set forth in Procedure ll below.
• the products of the Winters patent as described above could be converted into polymers containing recurring tertiary and/or quaternary groups by subjecting the polymers to quaternization with methyl chloride as set forth in Procedure II below.
• the epihalohydrins that can be used according to this invention to react with the amines include not only the well-known but various homologs, isomers, saturated or unsaturated so long as they are capable of reaction with an alkyl amine to produce a water soluble product containing recurring amine groups.
• the water soluble polymers can also be prepared by polymerizing epichlorohydrin by known manners and then reacting the polyepihalohydrin with an alkyl amine to produce a polymer having recurring amine groups.
• the resulting product may have to be quaternerized, for example, by a process similar to that set forth in Procedure ll below if the presence of the re curring tertiary and/or quaternary amine groups is desired.
• PROCEDURE 1 102 grams of dimethylaminopropylamine are added to a three-necked round flask containing 612 grams of water. The flask is placed in a water bath and is equipped with an agitator, a thermometer and a funnel with stopcock. After the solution is cooled to and maintained at C., 161 grams of epichlorohydrin are added to the aqueous solution in the flask slowly over a period of an hour. The molar ratio of the epichlorohydrin to the dimethylaminopropylamine is 1.75:1. The reaction is allowed to proceed for an additional minutes after all the epichlorohydrin is added to the aqueous solution and thereafter, the reaction product is acidified to a pH of about 6 with sulfuric acid.
• PROCEDURE II 452 grams of dimethylaminopropylamine in 820 ml. of water is reacted with 368 grams of epichlorohydrin (0.9:1 molar ratio of the epichlorohydrin to the dimethylaminopropylamine) in a round flask in the same manner as described in Procedure 1. After the reaction is completed, the resultant product is put in an autoclave together with 110 grams of sodium hydroxide, and is heated therein to 50C. under agitation. 300 grams of methyl chloride under a pressure in the range of 2.8 to 3.5 kg/Cm is then used to flush the autoclave and thereafter the autoclave is cooled and the contents are emptied. The resultant solution is adjusted to a solid content of 50 percent and a pH of about 6.
• the amount of polyelectrolytes which can most advantageously be used according to this invention will of course vary to some extent depending upon the particular polyelectrolyte selected for use and the brightness of the zinc plating desired.
• a basic solution containing sodium zincate and free sodium hydroxide is used, the deposit is a matte gray color with no luster at all.
• the deposit becomes semi-bright, and as additional polyelectrolyte is added, brighter plating will be obtained until maximum brightness is obtained. Additional amounts of the polyelectrolyte could of course be used if desired.
• Additional brightness can be obtained by adding conventional brightners such as the aldehyde brighteners including vanillin, hydroxybenzaldehyde, anisic aldehyde, bisulfite compounds of aldehydes, and so forth.
• the secondary brighteners mentioned above are optional for obtaining even brighter zinc plates if desired.
• the amount of such secondary brighteners, such as anisic aldehyde can be varied quite widely, as will be apparent to those skilled in the art.
• anisic aldehyde can be used in combination with the polyelectrolytes in an amount as low as 0.1 grams per liter and up to one gram per liter and even more.
• a small amount of cyanide, such as sodium cyanide, can be used in the plating solutions of this invention if desired.
• the advantageous results of this invention are not obtained if the amount of cyanide exceeds about 2 oz./gal.
• the presence of cyanide is, however, not essential for the production of bright zinc plate in accordance with the present invention.
• the baths according to this invention can be operated at conventional amperages for zinc plating baths. For example, anywhere from about 0 to 250 amps per square foot as determined by the Hull-Cell evaluation can be used. It is advantageous, however, to utilize between about 25 to 50 amps per square foot, and 25 amps per square foot is generally recommended for production plating.
• a zinc electroplating solution was prepared having the following composition:
• Zinc metal Caustic soda Condensation reaction product of epichlorohydrin and dimethylaminopropyl amine produced by Procedure ll having a molecular weight of 4000 5000 Anisic aldehyde bisulfite 1.6 oz/gallon l 6 oz/gallon 6 cc/gallon 0.04 g/gallon
• a plating test was run in a Hull cell. A steel panel was plated at 5 amperes for 2 minutes at room temperature with no agitation. The deposit was fairly bright from 1 asf to about 90 asf. Above this current density, however, the deposit was grey, matte and non-adherent. In addition, the panel lacked sufficient brightness in the -90 asf range.
• EXAMPLE II EXAMPLE Ill 1.5 g/l of 3-picolylamine was added to the bath described in Example I. The burned or the grey, matte and non-adherent zinc coating was eliminated over the entire surface of the panel plated but the overall brightness of the panel over the entire current density range was not as good as when 2-aminopyridine was used.
• EXAMPLE IV 0.8 g/l of 2-aminopyridine was added to the bath described in Example I and plated as described therein. This panel had similar advantageous results to the zinc plated panel described in Example 11.
• EXAMPLE V EXAMPLE Vl An 80 gallon electroplating bath was prepared having the following composition:
• Vanillin l2 cc/gallon 0.1 g/gallon Electrical boxes having deep recesses and sharp edges were plated in the above bath at an average current density of 60 asf. After plating, the parts showed severe burning on the outer edges.
• EXAMPLE V11 EXAMPLE Vlll To a bath as prepared in Example 1 was added 0.5 g/l (27% solution) of the reaction product of 1 mole of 2- aminopyridine and 1.3 moles of ethylene oxide prepared by the above described procedure. A steel panel 50 plated in a Hull cell at 5 amps for 2 minutes was bright from O to greater than 250 asf.
• a Zinc electroplating solution was prepared having the following composition:
• EXAMPLE X A plating solution containing zinc metal at a level of 1.6 oz/gal, of sodium hydroxide at a level of 16 oz/gal with 20 cc/liter tetraethylene pentameine resulted in a spongy matte deposit.
• An aqueous zincate bath having a pH of about 12 and above for electroplating bright metallic zinc deposits on substrates over a wide current density range which comprises 1. an aqueous alkaline solution containing less than about 2 oz./gal. of cyanide;
• an amine brightening agent other than the amino substituted pyridine or quinoline compound in sufficient amount to increase the brightness of the entire deposit.
• substituted pyridine compound is the reaction product of an epoxide and a substituted pyridine, said reaction product being produced by reacting the epoxide and a substituted pyridine for a sufficient length of time and in a molar ratio sufficient to form the reaction product which is soluble in the aqueous zincate bath.
• amino-pyridine is 2-aminopyridine or 3-aminopyridine.
• amine brightening agent is a water soluble reaction product of an amine and an epihalohydrin or an amine and a polyepihalohydrin containing repeating amino groups and having a molecular weight above about 250, said reaction between the amine and the epihalohydrin and the amine and the polyepihalohydrin being carried out for a sufficient length of time, and said reactants being present in such a molar ratio so as to produce a polycondensate having repeating amino groups and having a molecular weight above about 250, but below that which would render the polymer insoluble in the alkylene zincate bath.
• the method of electrodepositing, bright metallic zinc which comprises electrodepositing zinc on a substrate over a wide current density range from an aqueous zincate bath having a pH of about 12 and above containing 1. an aqueous alkaline solution containing less than about 2 oz./gal. of cyanide;
• an amine brightening agent other than the amino substituted pyridine or quinoline compound in sufficient amount to increase the brightness of the entire deposit.

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• Chemical & Material Sciences (AREA)
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• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electroplating And Plating Baths Therefor (AREA)
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• 1973
  • 1973-02-01 US US328782A patent/US3884774A/en not_active Expired - Lifetime
• 1974
  • 1974-01-31 FR FR7403322A patent/FR2216364B1/fr not_active Expired
  • 1974-01-31 GB GB463974A patent/GB1445823A/en not_active Expired
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