Classifications

• • C—CHEMISTRY; METALLURGY
  • C07—ORGANIC CHEMISTRY
  • C07D—HETEROCYCLIC COMPOUNDS
  • C07D213/00—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members
  • C07D213/02—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members
  • C07D213/04—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom
  • C07D213/60—Heterocyclic compounds containing six-membered rings, not condensed with other rings, with one nitrogen atom as the only ring hetero atom and three or more double bonds between ring members or between ring members and non-ring members having three double bonds between ring members or between ring members and non-ring members having no bond between the ring nitrogen atom and a non-ring member or having only hydrogen or carbon atoms directly attached to the ring nitrogen atom with hetero atoms or with carbon atoms having three bonds to hetero atoms with at the most one bond to halogen, e.g. ester or nitrile radicals, directly attached to ring carbon atoms
  • C07D213/78—Carbon atoms having three bonds to hetero atoms, with at the most one bond to halogen, e.g. ester or nitrile radicals
  • C07D213/81—Amides; Imides
  • C07D213/82—Amides; Imides in position 3
• • 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
• • 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 to an aqueous, alkaline galvanic bath without addition of cyanide ions as complexing agents for the deposition of zinc and zinc alloy coatings, which bath contains as additives bis-(N,N-diaminoalkyl)urea- ⁇ , ⁇ -dihaloalkyl copolymers or oligomers and 3-carbamoyl pyridinium compounds quaternized in the 1-position. Furthermore, the invention relates to a process for the deposition of bright and even zinc and zinc alloy coatings in which the bath is used.
• Such metal coatings are used for improving corrosion properties and for achieving certain optical properties.
• the automotive industry has used electroplated zinc for decades in order to provide highly corrosion-resistant coatings at reasonable cost.
• Cyanide-free zinc electrolytes and corresponding alloy baths can be classified into two types of baths, namely weakly acidic zinc electrolytes (containing zinc chloride or zinc sulfate) and alkaline zinc electrolytes.
• Weakly acidic zinc baths result in the deposition of a uniformly bright zinc layer.
• they have the disadvantage that their current efficiency is always 100% across a wide range of current densities.
• this may be advantageous since the electric current is used only for the deposition of zinc.
• this results in excessively thick zinc layers in areas of high current density and to thin zinc layers in areas of low current density.
• the ratio of the zinc layer thickness in the area of high current density to the zinc layer thickness in the area of low current density is referred to as layer thickness distribution and should ideally be 1 (scattering coefficient). From a technical and functional point of view, the zinc layer on the substrate should have the same or approximately the same layer thickness across the entire substrate and should have high brightness.
• a good layer thickness distribution may be achieved by lowering the current efficiency in the area of high current density while the current efficiency is maintained in the area of low current density. So far, this kind of equalizing the zinc layer thickness across a wide range of current densities has been achieved in the deposition of zinc from alkaline, cyanide-free electrolytes.
• Alkaline zinc electroplating baths are generally constituted on the basis of an aqueous solution of zincate ions in the presence of alkali metal hydroxides.
• DE 25 25 264 and U.S. Pat. No. 3,884,774 describe such electrolytes; however, the zinc layers obtained according to these documents do not show a uniform layer thickness distribution.
• EP 1 114 206 B1 describes a formulation consisting of quaternary derivatives of pyridinium-3-carboxylic acid, copolymers consisting of N,N-bis-[3-(dialkylamino)-alkyl]ureas with ⁇ , ⁇ -dihaloalkanes and an aromatic aldehyde, which are characterized in that the formation of bubbles frequently described in connection of the deposition of zinc can be avoided.
• Further copolymers of the aforementioned type are described in U.S. Pat. No. 5,405,523, U.S. Pat. No. 5,435,898 and WO 2004/044269 A2.
• WO 2004/044269 A2 uses reducing sugars in order to obtain bright depositions.
• a disadvantage of this method is the high concentration of reducing sugars which results in increased COD and TOC contents in the effluent water.
• copolymers described in EP 1 114 206 B1, U.S. Pat. No. 5,405,523 and U.S. Pat. No. 5,435,898 are used as brightening agents together with the commercially readily available quaternized derivatives of nicotinic acid, in particular, N-benzyl-nicotinate.
• U.S. Pat. No. 4,071,418 describes a bath formulation consisting of a quaternary pyridinium derivative and a cationic copolymer of a diamine with 1,3-dihalopropane-2-ol.
• the invention provides an aqueous, alkaline, cyanide-free electrolyte bath for the deposition of zinc and zinc alloy coatings on substrate surfaces, which bath comprises the following components:
• R 1 in formula II represents substituted aryl of the following formulae R1a to R1I:
• FG represents a residue selected from the group consisting of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy, hydroxy, trifluoromethyl, allyl, propargyl-, 4-sulfobutyl, 3-sulfopropyl, 4-carboxybutyl, 3-carboxypropyl residues, hydrogen and halogens, selected from fluorine, chlorine and bromine, and R 1 ′ in formula III represents but-2-enyl, but-2-ynyl or aryl of the following formulae R1′a to R1′ r:
• FG represents a residue selected from the group consisting of carboxy, ester, sulfonic acid, carbamoyl, amino, cyano, alkyl, alkoxy, trifluoromethyl residues, hydrogen and halogens, selected from fluorine, chlorine and bromine, wherein all rings or individual fused rings may be substituted.
• residues R 1 and R 1 ′ in formulae II and III are bonded to the pyridinium residue via a methylene group.
• Preferred araliphatic hydrocarbon residues are, for example, benzyl (R1a) and naphthyl methyl (R1b).
• fluorides, chlorides and bromides may be used as halides.
• the bath according to the invention may contain compounds, which are similar, with respect to their physical and chemical properties, to the halides, i.e., so-called pseudo-halides.
• pseudo-halides are known to the skilled person as such and are described, for example, in Römpp-Lexikon, Chemie, 10 th edition, page 3609.
• pseudohalides also comprise residues such as mesitylate and triflate.
• the soluble polymers of general formula I contained in the bath may be obtained according to EP 1 114 206 B1 by reaction of N,N-bis-[(dialkylamino)-alkyl]-ureas with ⁇ , ⁇ -dihaloalkanes.
• a particularly preferred copolymer of this class is, apart from the compounds described in EP 1 114 206 B1, MirapolTM WT available from Rhodia or LugalvanTM P available from BASF.
• the polymer of formula I is contained in the bath according to the invention preferably in an amount of 0.1 to 50 g/l, more preferably 0.25 to 10 g/l.
• the bath may contain a combination of different soluble polymers of general formula I.
• the electroplating baths according to the invention contain an inorganic alkaline component, preferably a hydroxide of an alkali metal and, particularly preferably, sodium hydroxide, potassium hydroxide and/or lithium hydroxide, in order to adjust the pH of the bath to at least 10 and preferably to at least 11. To this end, amounts of 50 to about 250 g/l, preferably 90 to 130 g/l of the alkaline component may be used.
• an inorganic alkaline component preferably a hydroxide of an alkali metal and, particularly preferably, sodium hydroxide, potassium hydroxide and/or lithium hydroxide
• the electroplating baths according to the invention generally contain zinc ions at concentrations ranging from about 0.1 to about 100 g/l, concentrations of 4 to 30 g/l being preferred.
• the zinc ion may be present in the bath according to the invention in the form of a soluble salt, for example zinc oxide, zinc sulfate, zinc carbonate, zinc acetate, zinc sulfamate, zinc hydroxide, zinc tartrate.
• the baths according to the invention contain about 0.1 to 50 g/l of metal ions
• suitable metal salts are hydroxides, sulfates, carbonates, ammonium sulfates, sulfamates, acetates, formates and halides, preferably chloride and bromide.
• Suitable alloying metals are preferably cobalt, nickel, manganese and/or iron.
• the concentration of the alloying metal ions in the baths according to the invention may be varied across a wide range and preferably is 0.01 to 100 g/l. Since different types of alloys require different contents of alloying metals, for example in order to improve protection against corrosion, this concentration varies from metal ion to metal ion.
• the baths according to the invention contain about 0.1 to 50 g/l of nickel ions as alloying metal.
• Suitable nickel salts are nickel hydroxide, nickel sulfate, nickel carbonate, ammonium nickel sulfate, nickel sulfamate, nickel acetate, nickel formate and nickel halides.
• the electrolyte bath contains zinc in an amount of 0.1 to 30 g/l and cobalt in an amount of 10 to 120 mg/l, nickel in an amount of 0.3 to 3 g/l, manganese in an amount of 10 to 100 g/l and/or iron in an amount of 10 to 120 mg/l.
• the electrolyte baths according to the invention contain the aforementioned aromatic heterocyclic nitrogen-containing compounds of general formulae II and III for substantial improvement of leveling and brightness properties of the deposited layers across a wide range of current densities. Therefore, the compounds of formulae II and III are hereinafter referred to as brightening agent according to the invention.
• Preferred compounds of formulae II and III are 1-benzyl-3-carbamoyl-pyridinium-chloride, 1-(2′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(2′-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(2′-methoxy-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(2′-carboxy-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(2′-carbamoylbenzyl)-3-carbamoyl-pyridinium-chloride, 1-(3′-chloro-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(3′-fluoro-benzyl)-3-carbamoyl-pyridinium-chloride, 1-(3
• the brightening agents can be readily prepared by reacting the corresponding nicotinic acid amide derivatives with the corresponding benzyl halides in a suitable solvent, such as ethanol, propanol, iso-propanol, butanol, iso-butanol, methanol or their mixtures, DMF, DMAc; NMP, NEP, in substance or in an aqueous medium, while heating under normal or increased pressure.
• a suitable solvent such as ethanol, propanol, iso-propanol, butanol, iso-butanol, methanol or their mixtures, DMF, DMAc; NMP, NEP, in substance or in an aqueous medium, while heating under normal or increased pressure.
• the reaction times required range from 1 to 48 hours, depending on the starting material used. In this connection, apart from conventional sources of heat, a microwave oven may be used.
• the pyridinium compounds obtained can either be used directly as the aqueous or alcoholic reaction solution or they can be isolated after cooling by filtration or by removal of the corresponding solvent.
• the compounds can be purified by recrystallization from a suitable solvent such as ethanol, precipitation or column chromatography.
• the bis-pyridinium compounds of general formula II can be prepared according to U.S. Pat. No. 6,652,728.
• the compounds of formula II or Ill can be used alone or as a mixture at a concentration of 0.001 to 20 WI, preferably of 0.001 to 10 g/l.
• the bath may contain a combination of pyridinium compounds of formulae II and III.
• the baths according to the invention may be prepared according to conventional methods, for example by adding the specific amounts of the aforementioned components to water.
• the amount of the basic component, such as sodium hydroxide, should be sufficient to achieve the desired pH of the bath of at least 10 and preferably above 11.
• the baths according to the invention deposit a bright, even and ductile zinc or zinc alloy layer at any conventional temperature of about 15° C. to 50° C., preferably 20° C. to 30° C., more preferably about 25° C. At these temperatures, the baths according to the invention are stable and effective over a wide range of current densities of 0.01 to 10 A/dm 2 , preferably 0.5 to 4 A/dm 2 .
• the baths according to the invention can be used in continuous or batch-wise mode and the components will have to be replaced from time to time.
• the components of the bath can be added alone or in combination.
• Table 1 shows, according to a particularly preferred embodiment, the influence with respect to the layer thickness (and thus current efficiency), brightness and layer thickness distribution in the electrolytes according to the invention for deposition of a zinc layer (using 10 4 mmol/l of pyridinium compound and a polymeric additive according to Preparation Example 2.2 of EP 1 114 206 B1):
• the novel electrolytes according to the invention show markedly better layer thickness distributions while the current efficiency is increased at the same time.
• current efficiencies which are 10 to 30% (in the area of high current density) or 30 to 50% (in the area of low current density) higher compared to the classic pyridinium compound.
• much higher current efficiencies in the area of low current density are very interesting in connection with applications using drum electroplating methods.
• a further advantage of the electrolytes according to the invention, compared to the electrolyte of EP 1 114 206 B1 is the surprisingly lower consumption of the quaternized nicotinamide derivatives according to the invention, compared to the N-benzyl-nicotinate.
• the consumption of pyridinium compounds acting as brightening agent in the electrolytes according to the invention is significantly lower and thus more economical than the conventionally used pyridinium derivatives based on nicotinic acid.
• the baths according to the invention may contain known levelling agents such as 3-mercapto-1,2,4-triazole and/or thiourea, thiourea frequently being preferred.
• the electrolyte bath according to the invention may contain additional brightening agents from the group of sulphur compounds, aldehydes or bisulfite adducts thereof, ketons, amines, polyvinyl alcohol, polyvinyl pyrrolidone, proteins or reactions products of halohydrines with aliphatic or aromatic amines, polyamines or heterocyclic nitrogen compounds and mixtures thereof.
• aromatic aldehydes from the group of 4-hydroxybenzaldehyde, 4-hydroxy-3-methoxy-benzaldehyde, 3,4-dimethoxy-benzaldehyde, 3,4-methylenedioxy-benzaldehyde, 2-hydroxy-benzaldehyde and mixtures as well as bisulfite adducts thereof, in an amount of 0.001 to 1.0 g/l.
• aromatic aldehydes or their bisulfite adducts as additional brighteners, for example 4-hydroxybenzylaldehyde, 4-hydroxy-3-methoxybenzaldehyde, 3,4-dimethoxybenzaldehyde, 3,4-methylenedioxybenzaldehyde, 2-hydroxybenzaldehyde or mixtures thereof as well as bisulfite adducts thereof, is unnecessary.
• the electrolyte bath according to the invention thus contains no aromatic aldehydes or their bisulfite adducts as additional brighteners, in particular, it contains no 4-hydroxybenzylaldehyde, 4-hydroxy-3-methoxybenzaldehyde, 3,4-dimethoxybenzaldehyde, 3,4-methylenedioxybenzaldehyde or 2-hydroxybenzaldehyde or bisulfite adduct thereof.
• the electrolyte bath according to the invention may contain a complexing agent or a water softening agent.
• the complexing agent is preferably a chelate forming agent, which is preferably present in an amount of 2 to 200 g/l.
• the electrolyte bath according to the invention can also contain, as leveling agent, a sulfur compound, for example, 3-mercapto-1,2,4-triazole and/or thiourea, preferably in an amount of 0.01 to 0.50 g/l.
• a sulfur compound for example, 3-mercapto-1,2,4-triazole and/or thiourea, preferably in an amount of 0.01 to 0.50 g/l.
• aqueous, alkaline baths according to the invention can generally be used for all types of substrates on which zinc and zinc alloys can be deposited.
• suitable substrates are soft steel, spring steel, chromium steel, chromiummolybdenum steel, copper, copper/zinc alloys.
• the invention also provides a process for the galvanic deposition of zinc and zinc alloy coatings on conventional substrates, wherein the electrolyte bath according to the invention is used.
• the deposition of coatings is preferably carried out at a current density of 0.01 A/dm 2 to 10 A/dm 2 and at a temperature in the range of 15 to 50° C., preferably 20 to 30° C., more preferably about 25° C.
• the process according to the invention may be carried out, for example, as barrel electroplating process when applied to small pieces and as a rack electroplating process when applied to larger pieces.
• the process involves the use of anodes, which may be soluble, for example, zinc anodes, which may serve as zinc ion source at the same time so that the zinc deposited on the cathode is replaced by dissolution of zinc from the anode.
• insoluble anodes for example, platinized titanium mixed oxide anodes
• zinc ions and/or further metal ions removed from the electrolyte by deposition of the alloy have to be added to the electrolyte in other ways, for example by using a zinc dissolution container.
• the process according to the invention can be carried out with injection of air, with or without agitation of the substrate, which has no negative effects on the coatings obtained.
• the electrode regions may be separated or membrane anodes may be used.
• the current source may be a conventional rectifier or pulse rectifier.
• An electrolyte having the following composition is used:
• the thickness layer coefficient is the ratio of the layer thickness at high current density and the layer thickness at low current density.
• N-benzylnicotinate corresponds to the teaching of the prior art (Example 14 of EP 1 114 206 B1).
• both electrolytes are used in a 5 liter bath as in the Application Examples described above in order to electroplate Norton sheets.
• a Norton sheet is electroplated at 6 A for 30 minutes, whereafter the layer thickness and the visual appearance are evaluated.
• the zinc and nickel contents which could be determined by titration with EDTA solution, were sufficient and the visual appearance of the Norton sheets was good and bright, the electroplating is continued.
• a complete bath test is carried out, consisting of the Hull cell test (as described above) and the determination of the zinc and NaOH concentration. If too little zinc (target value: 10 g/l zinc oxide) or NaOH is present, the missing amount is added. After the brightness has decreased, the corresponding pyridinium compound is replenished.
• An electrolyte having the following composition is used:
• the electrolyte 250 ml of the electrolyte are filled into a Hull cell.
• a nickel anode is used.
• the cathode is electroplated at 1A for 15 minutes.
• the metal sheet is rinsed and dried with compressed air.
• the layer thickness is measured at two points (3 cm from the bottom edge and 2.5 cm from the right- and left-hand edge) at high (3 A/dm 2 ) and low current density (0.5 A/dm 2 ).
• the measurement of the nickel content is carried out at the same places. The measurement is done by XRF and four points in each position so as to minimize measurement errors.
• the coating obtained was highly bright.
• the electrolyte suitable for deposition of a zinc iron layer was prepared.
• the electrolyte had the following composition:
• a Hull cell sheet was coated for 10 minutes at 1 ampere. A very bright deposition is obtained.
• the Hull cell sheet was rinsed and chromated in a commercially available black chromation for zinc iron layers (TridurTM black liquid ZnFe, Atotech). The chromated sheet showed good black coloration.

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• 2006
  • 2006-06-21 EP EP06012766A patent/EP1870495A1/de not_active Withdrawn
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