EP1015670A1 - Mit magnesium kolorierte oder aus magnesium-legierung bestehende gegenstände - Google Patents

Mit magnesium kolorierte oder aus magnesium-legierung bestehende gegenstände

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Publication number
EP1015670A1
EP1015670A1 EP98914164A EP98914164A EP1015670A1 EP 1015670 A1 EP1015670 A1 EP 1015670A1 EP 98914164 A EP98914164 A EP 98914164A EP 98914164 A EP98914164 A EP 98914164A EP 1015670 A1 EP1015670 A1 EP 1015670A1
Authority
EP
European Patent Office
Prior art keywords
dye
article
magnesium
species
dyes
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
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Application number
EP98914164A
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English (en)
French (fr)
Other versions
EP1015670A4 (de
Inventor
John Arnold Macculloch
Philip Nicholas Ross
Geoffrey Stephen Henshaw
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Magnesium Technology Ltd
Original Assignee
Magnesium Technology Ltd
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Filing date
Publication date
Application filed by Magnesium Technology Ltd filed Critical Magnesium Technology Ltd
Priority claimed from PCT/NZ1998/000039 external-priority patent/WO1998042895A1/en
Publication of EP1015670A1 publication Critical patent/EP1015670A1/de
Publication of EP1015670A4 publication Critical patent/EP1015670A4/de
Withdrawn legal-status Critical Current

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
    • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
    • C25D11/00—Electrolytic coating by surface reaction, i.e. forming conversion layers
    • C25D11/02—Anodisation
    • C25D11/30—Anodisation of magnesium or alloys based thereon

Definitions

  • the present invention relates to a method of colouring magnesium or magnesium alloy material having an anodized or other oxidised surface (as in the chemical meaning, ie; a transfer to a higher oxidation state, not limited to magnesium oxide) of the magnesium or magnesium alloy and to the product of such a process and related apparatus and procedures.
  • the present invention also consists in a related procedure for increasing corrosion resistance.
  • the colouring of magnesium alloy articles that have been anodized (or otherwise chemically oxidised) has defeated most attempts by experimenters attempting to provide a range such as is available for anodized aluminium. Whereas the colouring of anodized aluminium is available through several methods, there are no simple analogies available for magnesium even though much research has been directed towards this goal over a period of some years.
  • colouring aluminium As most anodic films generated on aluminium have a regular hexagonal pore structure, characterised by the spacing, size and even distribution of the pores, several options for colouring aluminium involve inducing colouring agents (dyes, metal ions or pigments) to enter the pores. Once the colouring step has concluded, the article is generally "sealed", a treatment that closes the pores and in effect, locks the colouring material into place. Transition metal ions achieve a strong colouring effect when used in this manner.
  • Magnesium anodic films feature a pore structure as well, but unlike aluminium this is not well characterised and the pores are unevenly distributed.
  • the pores range in diameter, but are generally larger than the aluminium pores.
  • the anodic film is translucent or opaque, not transparent, therefore any colouring effect from a species introduced into a pore may be more limited.
  • Acid colouring systems are therefore usually inapplicable to magnesium and will ordinarily result in attack of the substrate metal as well as the anodic film.
  • anodising the metal is to increase corrosion resistance
  • using a colouring process that attacks the substrate or anodic film is contra-indicated.
  • magnesium is a highly reactive metal, considerably more so than aluminium, and the presence of such species at the base of the film pores would introduce micro galvanic cells ready to initiate corrosion.
  • corrosion resistance may be a reason for anodising magnesium substrates an increase in the corrosion susceptibility of the substrate is not usually commercially acceptable.
  • US Patent 4,551,211 Ube Industries discloses a method of anodising a magnesium article in a solution containing very high concentrations of aluminium (as aluminate ion) resulting in a combined magnesium/aluminium oxide matrix which can then be coloured using conventional aluminium dyeing technology.
  • the process is notable for its difficulties in application and expensive chemicals being required (iodides).
  • the colouring method there disclosed cannot be extended to-other anodic films.
  • US Patent 4,551,211 admits to the complexity of the process.
  • the present invention is directed to a method of colouring magnesium or magnesium alloys which provides a material having a coloured yet protection providing anodized or other oxidised surface.
  • other oxidised surface is not meant a modification of the surface with an oxidised metal of a different species as in US
  • the present invention consists in a method of colouring a magnesium or magnesium alloy article, said method comprising or including the steps of ensuring the article has, or providing the article with an anodized or other oxidised surface of the magnesium or magnesium alloy, and contacting said anodized or other oxidised surface with at least one species of chromophoric moiety in a liquid carrier in conditions, or in a sequence of conditions, not substantially prejudicial to the integrity of said anodized or other oxidised surface yet which results in the chromophore(s) becoming associated (directly or via a moiety or species attached to the chromophore) with the surface by a reaction or adsorption.
  • said conditions exclude the prospect of an aluminium build up on said surface even should the magnesium have been alloyed with aluminium.
  • the carrier is aqueous.
  • said surface is anodized.
  • said surface is chemically oxidised.
  • the conditions include elevated temperature(s).
  • the step of contacting is by immersion although spraying is another option to find favour.
  • the method includes washing the anodized or other oxidised surface prior to contact with said at least one species of chromophoric moiety in a liquid carrier.
  • the method includes a washing step subsequent to the contact with said at least one chromophoric moiety in a liquid carrier.
  • Preferably said conditions involves a near neutral, neutral or alkaline pH.
  • saidpH is alkaline or at least as alkaline as the dye process will allow.
  • said species is selected from the group consisting of reactive dyes, direct dyes, VAT dyes, sulphur dyes and disperse dyes (as defined in the Colour Index).
  • the species is one of the group consisting of reactive dyes, VAT dyes and sulphur dyes.
  • said species is selected from the group consisting of vinyl sulphones, monochloro triazines, dichloro triazines, pyrimidines, phthalocyanines, quinoxalines, aniline derivatives, monofluoro triazines, anthraquinones, indigo and halogenated indigo derivatives, polysulphides, and diazo phenols.
  • said species is selected from the group consistmg of vinyl sulphones, monochloro triazines, dichloro triazines, pyrimidines, phthalocyanines, quinoxalines, monofluoro triazines, anthraquinones, indigo and halogenated indigo derivatives, polysulphides, and diazo phenols.
  • the invention comprises or includes (i) providing a bath containing a sulphur textile dye together with alkali and a reducing agent such that the dye is present in its water-soluble reduced leuco form;
  • said bath is at approximately 90 °C for approximately l A an hour.
  • said sulphur textile dye is provided at approximately double the normal concentration employed for textile dyeing.
  • the invention comprises or includes (i) providing a bath containing a VAT textile dye together with an alkali and reducing agent such that the dye is present in its water soluble leuco form; (ii) immersing said article in said bath; and (iii) immersing said article in a mildly acidic oxidising solution to form the dye on the surface of the article.
  • said reducing agent is sodium dithionite.
  • said article is immersed at approximately 70 ° C for approximately 30 minutes.
  • said VAT textile dye is provided at double the normal concentration employed for textile dyeing.
  • said article is immersed in said mildly acidic oxidising solution for approximately five minutes.
  • the invention comprises or includes (i) providing a bath containing a vinyl sulphone reactive textile dye; (ii) immersing said article in said bath; and (iii) washing said article.
  • said bath is provided at a pH of approximately 12 and said article is immersed for approximately 30 minutes at at least 60 °C (preferably 80 °C),
  • said bath contains a reactive dye, and at least one of sodium carbonate, sodium hydroxide or sodium silicate.
  • said bath contains a reactive dye in a concentration-of 5g/L and sodium carbonate, also at a concentration of 5g/L and sodium hydroxide at a sufficient concentration to raise the pH to about 12.
  • a reactive dye in a concentration-of 5g/L and sodium carbonate, also at a concentration of 5g/L and sodium hydroxide at a sufficient concentration to raise the pH to about 12.
  • said washing is in water at at least 60 °C (preferable with a wetting agent, eg; ethylene glycol).
  • the invention comprises or includes (i) providing a bath containing a monochloro triazine reactive textile dye; (ii) immersing said article in said bath; and (iii) washing said article.
  • said bath and said article is immersed for approximately 30 minutes at approximately 60 °C.
  • said bath contains a reactive dye, and at least one of sodium sulphate, sodium chloride, carbonate and sodium hydroxide.
  • said bath comprises a reactive dye in a concentration of 0.5 - 2% and Na 2 S0 4 concentration is equal to dye concentration, sodium carbonate 0.5 - 1% and NaOH 0.25%.
  • washing is in water at 80 °C.
  • said surface is anodized and said at least one species of chromophoric moiety in a liquid carrier is a reactive dye of a kind having a vinyl sulphone functional group and wherein the conditions are within a temperature range of from 30 to 100°C during an immersion or spray presentation of the liquid dye composition to the anodized surface for at least 10 minutes and thereafter a rinsing step with water at an elevated temperature.
  • said contact time is about 30 minutes.
  • said rinsing step is with hot water containing a wetting agent and the temperature of the aqueous rinsing composition is 80 °C or greater.
  • said temperature of the immersion or spraying with the liquid dye composition is at about 60 °C.
  • the dye has a concentration of at least about 0.5% w/v in an aqueous system.
  • said surface is anodized and wherein the at least one species of chromophoric moiety in a liquid carrier is a reactive ⁇ lye of a kind having a monochloro triazine functional group and the conditions during the contact by immersion or spraying is contact at an elevated temperature.
  • the contact time is for a period of from 30 to 60 minutes.
  • the elevated temperature of the contact is at about 70 °C or higher.
  • the dye concentration is from 0.5% to 2% w/v.
  • sodium sulphate at substantially equal concentration to the dye, sodium carbonate at 0.5 to 1.0% w/v and sodium hydroxide to a concentration of about 0.25% w/v.
  • a rinsing step with hot water containing a wetting agent and at a temperature of 80 °C or greater.
  • said at least one species of chromophoric moiety in a liquid carrier is that of a reactive dye having a dichloro triazine functional group or a monofluoro or difluoro triazine functional group.
  • a reactive dye having a dichloro triazine functional group or a monofluoro or difluoro triazine functional group is that of a reactive dye having a dichloro triazine functional group or a monofluoro or difluoro triazine functional group.
  • the conditions are similar to those for monochloro triazine functional groups.
  • the at least one species of chromophoric moiety in a liquid carrier is a reactive dye of the pyrimidine type.
  • the at least one species of chromophoric moiety in a liquid carrier is that of a vat dye.
  • the dye is an anthraquinone or indigo derivative.
  • vat dye is dispersed in water and reduced to water soluble leuco form using a combination of a reducing agent and alkali.
  • said leuco dye is used to colour anodized magnesium article by immersion or spraying.
  • the temperature of leuco dye is elevated. Most preferable 60 °C or higher.
  • pH of leuco dye is 11.5 or greater.
  • leuco dye dyed article is rinsed in cold water (eg; 5 seconds) and then oxidised so that leuco dye is converted to insoluble pigment.
  • the at least one species of chromophoric moiety in a liquid carrier is that of a sulphur dye.
  • the moiety is attached to a polysulphide.
  • the sulphur dye is dispersed in water and reduced to water soluble leuco form (thiol form) using a combination of a reducing agent and alkali.
  • said leuco dye is used to colour anodized magnesium article by immersion or spraying.
  • the temperature of leuco dye is elevated. Most preferable 60 °C or higher.
  • pH of leuco dye is 11.5 or greater.
  • leuco dye dyed article is rinsed in cold water (eg; 5 seconds) and then oxidised so that leuco dye is converted to insoluble pigment.
  • the at least one species of chromophoric moiety in a liquid carrier is a direct dye.
  • said direct dye comprises a chromophoric moiety attached to a sodium sulphonate group.
  • direct dye is present in solution 0.5 to 2% w/v with sodium sulphate 0.5 to 2% w/v and, optionally, sodium carbonate to a concentration of about 0.25 to 1% w/v.
  • an anodic potential of approximate 10 to 20 V DC may be applied to the anodized article.
  • temperature of dye solution is at least 60 °C.
  • dyed article is rinsed after dyeing.
  • the at least one species of chromophoric moiety in a liquid carrier is a disperse dye.
  • dye is evenly dispersed in water to the extent of at least 0.25% w/v.
  • a carrier being an ester is added to aid dyeing.
  • the article is introduced into the dye dispersion at 100°C or greater (eg; under pressure) and maintained in such contact for 20 to 90 minutes.
  • the article is subsequently rinsed.
  • the present invention consists in a method of increasing the corrosion resistence of an anodized magnesium or magnesium alloy surface which comprises the step of colouring such a surface by a process as previously defined
  • the at least one species of chromophoric moiety in liquid carrier is that of a reactive dye of a kind having a vinyl sulphone functional group.
  • the at least one species of chromophoric moiety in a liquid carrier is an acid dye using an acid which forms magnesium salts.
  • said acid is lactic acid.
  • the contact step with the liquid carried chromophoric moiety or moieties is a multiple step process.
  • Such multiple step process may result from multiple dipping, sequential spraying or a hybrid of dipping and spraying.
  • chromophoric moieties are used such as might result from mixed dyes.
  • the present invention consists in a magnesium or magnesium alloy material having a coloured anodized or other oxidised surface, said colouring having been achieved using a method in accordance with the present invention. Preferred forms of the present invention will now be described.
  • Figure 1 is a simple flow diagram showing the optional steps sometimes preferred.
  • Preferred surfaces to be coloured include those anodized by a process such as disclosed in PCT/NZ96/00016 (WO 96/28591) (Barton) or as disclosed in our PCT International Application filed simultaneously herewith.
  • the anodic film formed on aluminium is transparent in thin films and colours resulting from pigments or dyes deep within the pores therefore impart an overall colour to the film. Aluminium dye systems cannot be applied directly to magnesium anodic films.
  • Films formed on magnesium substrates are not transparent and have a natural colour. This is sometimes slightly off-white, but can be quite dark, depending on the electrolyte and conditions of anodisation. Colouring such a film would not be a simple matter of introducing a dye into the pores, which in any case are irregular and typically have diameters ranging from 2 m to 5 ⁇ m.
  • a colorant suitable for use on magnesium therefore has to mask whatever natural colour the surface has in addition to providing a strongly adherent layer itself. It is almost inevitable that any suitable method for colouring magnesium will add another layer to the surface owing to the translucent nature of the coating.
  • Some conversion coatings are available for use on magnesium substrates and these produce, in some instances, strongly coloured substrates.
  • British Patent 493,935 describes a method by which a chromate or permanganate conversion coating may be formed on a magnesium article. The coatings formed by this method are typically very dark and even black. Such is not considered "colouring" for the present purpose as the colour cannot be controlled and the coating formed is not a true anodic film. The process cannot be applied to an anodic film or an already existing other oxidised coating.
  • One class of aluminium dyes comprises inorganic compounds that result from a two-step process in which an insoluble colour is precipitated in the second stage of the process.
  • the first stage introduces a water-soluble species to the pores in the aluminium oxide anodic film.
  • This species is adsorbed onto the surface of the anodic film.
  • the diffusion of these species into the pores in the anodic film is governed by the surface charge on the film, known as the zeta potential. Ordinarily this is positive, but in suitable electrolytes it may be changed. Double dip processes only work in the correct sequence.
  • binary inorganic salt pairs that may be used to colour an anodic coating on aluminium include:
  • Organic colouring may also be employed on aluminium, although in most cases the dyes are adsorbed rather than undergoing a chemical reaction with -the substrate.
  • Acid and substantive dyestuffs normally react with the substrate but on aluminium anodic films they do not, although a colour is produced.
  • the colour is not particularly wash or light fast.
  • the dyes that work on aluminium are acid based and will usually have an adverse effect on the anodic film produced on magnesium.
  • aluminium dyes to colour magnesium is not effective except in the special case described above where the anodic film is modified to have a very high content of aluminium oxide (US Patent 4,551,211).
  • the range of existing colouring compounds includes simple pigments, such as titanium dioxide, which is used very widely as a brilliant white colour in paints, and exotic chemically-formed dyes which are the basis of photography.
  • a "pigment” may be regarded as being a coloured molecule which is insoluble and unreactive.
  • a pigment may colour an article by virtue of being in close contact with it although usually a carrier is required to ensure that it stays in place.
  • titanium dioxide is chemically inert and insoluble in aqueous solution or solvents. It is dispersed in paints and forms an opaque, brilliantly white layer when applied to articles in suspension in suitable carriers. Insolubility alone does not result in a pigment, as some insoluble colouring compounds may still react chemically with the substrate.
  • a “dye” on the other hand is often soluble in its carrier and in many cases it is chemically reactive with the substrate to which it will bond.
  • the “reaction” may be the formation of a clathrate compound, hydrogen bond or Van der Waals bond, while in others it may be a true chemical reaction.
  • a colouring agent is initially a dye, but is converted to a pigment once it has penetrated the substrate that is to be coloured.
  • a pigment is converted to a soluble, reactive form, which is then a dye, after application of which, it is converted back to a pigment.
  • We have determined that some colouring compounds designed for textile applications have application in colouring magnesium anodic films.
  • anodic or cathodic potential may be applied to the magnesium article. Such a potential is not applied to any textile material for use with the same dye systems. Also, there is no simple parallel to the fibre penetration processes that are usually part of the mechanism by which a textile fibre adsorbs dye molecules. In many cases where alkaline textile dyes are employed, sodium hydroxide present in the dye bath assists in penetration of the fibre because it promotes softening and swelling of the fibre.
  • the most applicable dyes are those applied to cellulosic fibres, such as cotton.
  • the cotton fibre consists of a central core of polyhydric alcohols surrounded by inert cellulose.
  • An anodic magnesium substrate has no such compounds on its surface and is completely inorganic in composition.
  • the electric fields employed in anodising magnesium are very high, resulting in deprotonation of the forming film and therefore the formation of magnesium oxide, rather than magnesium hydroxide.
  • the oxide ion, O 2' is instantly hydrolysed in aqueous solution:
  • the electric fields are often in the region of 1 x 10 9 volts per metre, sufficient to ensure the presence of oxide ions at active reaction sites.
  • Clearly anodized metal substrates are unlike the surfaces normally coloured using fibre-penetrating textile dyes.
  • these dyes comprise a chromophore which is a functional group which is attached to a reactive group that may bond either chemically or physically to the substrate. Since the same chromophore may be used in dyes that react differently to form the final coloured article, there is considerable overlap in the functional groups and a consideration of each class of reactive group is required.
  • a good example of chromophore overlap is in the area of turquoise dyes. Most turquoise dyes are based on phthalocyanine, which can form a range of blue and green hues when appropriately substituted, but will not readily form other colours. This chromophore is widely used to produce turquoise shades in reactive dyes and direct dyes, as well as other classes where appropriate.
  • dyes may be mixed to obtain colours different from those of the individual compounds.
  • mixing of dyes it must be borne in mind that the most effective mixing strategies are those which mix similar types of chromophores as well as reactive groups. Accordingly, while it is possible to mix a vinyl sulphone reactive dye with a monochloro triazine reactive dye, the results that are obtained may not be as expected owing to differences in reactivity. Also, even if, for instance, two vinyl sulphone reactive dyes are mixed, the result may not be the intermediate colour expected as the chromophores may not be compatible.
  • the hydrogen bonding of direct and vat dyes is not usually affected by a process involving a reactive dye as a first step and in some cases when not all reactive sites have been chemically bonded to a reactive dye, it is possible to double dip an article in a second reactive dye.
  • Dyeing an article that has been anodised may also be conducted for the reason of increasing the salt spray resistance of the article and not for any specific colour requirement in the final product.
  • the salt spray resistance of anodised magnesium test plates has been considerably enhanced when those test plates have been coloured. Improvements of 100% in salt spray resistance may be obtained in some circumstances, thereby justifying the colouring of anodised articles for this reason alone.
  • the dye may therefore react with the magnesium hydroxide bridging an oxygen atom as happens in the cellulose molecule. Since the magnesium hydroxide is formed on the surface, this form of dyeing would meet the requirements of the foregoing discussion.
  • a reactive dye to a magnesium anodic film is conducted in a solution containing reactive dye, and a base, at a bare minimum.
  • additional alkali, and sometimes an ionic salt can improve the dye exhaustion.
  • the dyeing reaction is more active under more alkaline conditions and the presence of salt may help aggregate the dye on the substrate surface owing to the common ion effect.
  • the reaction normally takes place at a temperature of around 60 °C and sometimes higher.
  • the dyeing reaction can be influenced favourably by applying an electric charge to the surface of the magnesium oxide. This can be done easily by means of the electrolytic apparatus used to anodize the substrate.
  • Hydrolysed dye is unavoidably present in the dye bath and some of this would diffuse into the pores of the magnesium article and adhere weakly to the surface. It seems that long after a reactive dye would be regarded by the textile industry as unsuitable for use owing to the extensively hydrolysed nature of the dye molecules, it is still possible to dye anodic films on magnesium. Often there is a slight shift in the shade obtained, presumably because the hydrolysed dye cannot bond chemically to the substrate and must be physically adsorbed.
  • hydrolysed dye may still provide satisfactory colouring, it is normal after dyeing to have to rinse well in hot aqueous solutions containing a wetting agent, to remove quantities of unreacted and poorly adherent dye as otherwise drying marks will affect the finish of the magnesium article.
  • the functional groups present in a reactive dye are normally vinyl sulphone or derivatives of trichloro triazine (cyanuric trichloride), such as monochloro triazine.
  • Some reactive dyes comprise two or more reactive groups. In cases where two reactive groups are present, a benefit may accrue from combining, for example, a vinyl sulphone with a monochloro triazine group. If one group is hydrolysed, the dye may still bond chemically to the substrate.
  • Reactive dyes have to be small molecules so as to penetrate the cellulose fibre thus enabling the reaction. This generally means one chromophore only, and this should most advantageously be a small group, for instance a monoazo or diazo compound. Often a reactive dye will have the following structure:
  • step #6 Repeat step #6 until all residues of poorly adherent hydrolysed dye are removed.
  • hydrolysed dye will leach from areas that are drying leaving drying marks on coloured articles. If necessary, such marks may be removed by re-rinsing in very hot or even boiling water.
  • Concentrations of reactive dyes used to colour magnesium are often greater than those employed on textile materials. There is no need to use auxiliaries which for textile application are present to aid in fibre penetration. It is common for reactive dyes for textile application to be applied progressively in a dye bath to which the dye is added, then after a period of time, salt and alkali. Such a method does not appear to be beneficial when dyeing magnesium substrates.
  • Rinse step highly preferred - hot water containing a wetting agent such as ethylene glycol 0.1 %, most preferably 80 °C (or greater) for one minute or longer.
  • a wetting agent such as ethylene glycol 0.1 %, most preferably 80 °C (or greater) for one minute or longer.
  • the article is a temperature where it will quickly dry and there will be no leaching of hydrolysed dye.
  • Direct dyes must be soluble in water.
  • a direct dye is applied to a cellulosic fibre by means of an aqueous solution in which a soluble ionic salt, commonly sodium sulphate or sodium chloride is dissolved.
  • the ionic salt assists in the dyeing process as it is believed that it aids in the charge transfer between the dye and the fibre, thus enhancing dye uptake by the fibre.
  • direct dyes contain sodium sulphonate groups. These ensure high water solubility and enable the dye molecule to form an ionic aqueous solution under conditions of alkaline pH:
  • the dye chromophore is negatively charged, it is attracted to any ions that are positively charged and repelled from negatively charged ions or surfaces.
  • the addition of an ionic salt is thought to assist in dyeing partly because of the "common ion” theory in which the dye is "salted out” or aggregates are formed.
  • a balance between exhaustion of the dye onto the substrate and that remaining in solution is established. The more alkaline the pH, the greater the water solubility of the dye. After a point, it also increases the affinity of the dye for the aqueous phase, rather than the insoluble fibre, hence it reduces exhaustion of the dye.
  • Direct dyes which contain a primary amino group attached to an aromatic ring may be diazotised and coupled to a naphthol component. This process tends to alter the dye colour as an azo group is added:
  • Cationic agents comprising a long chain hydrocarbon tertiary amine may be added to improve wash- fastness:
  • the dye may have affinity for the layer of hydroxide formed at the surface of the anodic film, the bonding that results being hydrogen bonding similar to that existing in water.
  • a direct dye to a magnesium article may involve a solution being made comprising the direct dye, a salt (commonly sodium sulphate) and in some cases, sodium carbonate or other suitable base.
  • a salt commonly sodium sulphate
  • sodium carbonate or other suitable base used as sodium sulphate
  • the use of sodium sulphate is preferred over the use of sodium chloride as chloride ions are noted as initiators of pitting corrosion and are therefore an unwanted species inside the pores of the anodic film.
  • the dye is normally heated to around 70 °C, although in some cases higher temperatures may be desired.
  • the dyeing is normally complete after 60 minutes.
  • anodic voltage applied to the dye bath can improve dye deposition substantially.
  • Such a voltage is ordinarily fairly low but depends on the thickness of the anodic film as this is an efficient insulator. Voltages less than 50 volts are normal.
  • Vat dyes are in fact insoluble pigments that are reduced to a water soluble leuco form in alkaline conditions for application to a fabric or anodized magnesium article, prior to being converted back to an insoluble pigment that is then highly light and wash fast on the finished article. According, the vat "dye” as such has a transitory existence in the leuco form. Vat dyes are described in the Colour Index under the heading "Vat Dyes”. Most are based on 9,10 anthraquinone, which of itself is colourless. However, once azo or other chromophores are attached to the ring structure, a wide range of colours may be obtained. o
  • Vat dyes include indigo, a substance originally of natural origin, which is not light fast, but which over time fades gradually in successive washes and is favoured for denim to create the characteristic "faded denim" look. Indigo and a few halogenated derivatives are still in use, although only indigo and tefrabromoindigo are of commercial importance currently.
  • Vat dyes are characterised by the presence of a keto group which can be reduced to an alcohol. This may then form a salt under conditions of alkaline pH: 0 ⁇ )CHOH (enol form) " )CR (salt of enol form)
  • the "salt" of the enol form is the leuco vat dye. This is water soluble and is therefore a true dye, rather than a pigment whereas the keto form is insoluble and is classed as a pigment.
  • vat dyes form hydrogen bonds to magnesium hydroxide molecules, thereby forming a dyed surface.
  • Oxidation of the reduced dye once it has formed a layer on the substrate, may be conducted by an oxidising bath or simply by sufficient exposure to air. Suitable oxidising baths comprise hydrogen peroxide or sodium perborate solutions, but alternatives including dichromates may be used. The optimum oxidising bath is acidified to a pH of 5-6 using acetic acid.
  • the colour of the reduced leuco form of the dye may not be identical to the insoluble pigment form and thus to some extent the final shade obtained may depend on the oxidant used.
  • An example of this is Cl Vat Green 9, which is a very dark olive green as oxidised by air or hydrogen peroxide. However, it can be oxidised in stronger oxidants to a neutral shade of black. 5.
  • Rinsing to remove any excess dye follows oxidation and in most cases there is a rinse stage between dye adsorption and oxidation to remove excess reducing agent and alkali, in addition to any unadsorbed dye.
  • vat dyes are affected by light in the leuco form, while others are precipitated by calcium ions in the water supply.
  • Deionised water should be used for preparation of vat dyes.
  • Anodized magnesium substrates must be very carefully rinsed prior to introduction to the bath containing the reduced leuco dye as free magnesium ions may also precipitate an insoluble compound from the dye bath.
  • vat dyes have some common features regardless of whether the dye is a indigoid or anthraquinone type.
  • the article may be oxidised in air (but the full oxidation process takes several days) or other oxidants.
  • Sodium or potassium dichromate, acidified with acetic acid is quite effective.
  • vat dyes may be operated at a higher concentration than this - these figures were intended for textiles. We found that a better shade resulted from doubling the concentration (this meant using 200ml/litre stock solution instead of lOOml/litre).
  • Vat dyes do not last in air because of the absorption of atmospheric oxygen and the downward drift of pH which should remain above 12.
  • the pH drift is due to the acids released by the sodium dithionite as it reduces the keto pigment to the enol form. If extra sodium dithionite has to be added, sodium hydroxide must be added with it, in a ratio of 1.2 parts sodium hydroxide to 1 part of sodium dithionite.
  • Sulphur dyes offer only a limited range of colours, none of them bright, because of the large size of the complex polysulphide rings formed, but they are fast and economical to apply to magnesium substrates. They are described in the Colour Index. Like vat dyes, sulphur dyes are in fact finely dispersed pigments which must be reduced to a soluble form in order for dyeing to proceed satisfactorily. After dyeing, the dye is oxidised back to the insoluble form, either by air or by an oxidising solution containing a suitable agent, often hydrogen peroxide or sodium perborate in aqueous solution.
  • a sulphur dye is normally a disulphide, which may be reduced to a thiol.
  • the exact chemistry of a sulphur dye is still not fully understood, but the reduction reaction proceeds:
  • the leuco form of the sulphur dye is applied to the article in aqueous solution at elevated temperatures, often around 80 ° C, in the presence of an ionic salt, often sodium chloride or sodium sulphate, which assists the exhaustion of the dye.
  • an ionic salt often sodium chloride or sodium sulphate
  • the reducing agent for the dye may be sodium dithionite but there are also proprietary agents available. Glyceraldehyde, hydroxyacetone, certain sugars, and various other agents are commonly found constituents of such reducing agents. Some proprietary reducing agents also contain alkalies, as these are also required to generate the soluble leuco form of the dye. This limits the requirement to add alkali separately to the bath.
  • Alkali is also required to enhance the solubility of the thiol.
  • sodium hydroxide is normally used although other alkalis serve equally well.
  • One problem in connection with sulphur dyes is that some dye decomposition may take place on the finished article. This results in the liberation of acid residues that may damage a magnesium part. For this reason, a finish in a mildly alkaline oxidising bath, rather than an acid solution is advised.
  • Sulphur dye bath made up and heated to around 90 °C.
  • Dye bath contains an ionic salt, sodium sulphate being prefened, although sodium chloride may also be used*.
  • Reducing agent is added to form the leuco dye. If sodium dithionite is used, sodium hydroxide or another base should be added as the reduction process generates acid, lowering the pH.
  • vat dyes Oxidise using hydrogen peroxide/sodium perborate solution as per vat dyes for twenty minutes at 50 °C.
  • various oxidants may be used.
  • One problem with sulphur dyes is that there is a tendency for the dyes to release acid upon decomposition, which is a negative feature for this will attack the anodic film.
  • the Colour Index lists a number of compounds where the chromophore is bonded to an intentionally insoluble compound to create a dye, which is applied as a finely dispersed suspension to dye certain types of fibres, such as polyesters. These dyes are thought to be solubilised either to a very slight extent either by a carrier, which is added to the bath, or at the surface of the fibre. The dissolved dye molecule can then migrate into the fibre. Monoazo and anthraquinone disperse dyes are common, but a range of varieties exist including diazo, nitrodiphenyl, methane, styryl, benzodifuranone and quinophthalone compounds. Carriers such as chlorobenzenes or aromatic esters increase the affinity of the substrate for the dye.
  • Acid dyes normally attack both the substrate and anodic film, a clearly unsatisfactory result.
  • lactic acid or similar organic acid which forms an insoluble magnesium salt for acetic acid in the general formulation it is possible to obtain a less aggressive formulation which can, for very short immersions or spray contact times, result in a stain that may be regarded as satisfactory colouration.
  • To conduct this procedure would entail:
  • a uniform stain may result without any significant surface or substrate degradation. However a longer immersion may result in a loss of the anodic or oxide film and attack of the substrate.
  • the coupling component is often a derivative of 3-hydroxy-2-naphthoic acid. Heat bath to elevated temperature, 70 C or greater.
  • salt sodium sulphate
  • coupler may be added to improve uptake of coupler.
  • diazonium salt In separate vessel, prepare diazonium salt. While this is best stabilised as the hydrochloride salt, it is preferable to avoid mineral acids because of their tendency to attack the substrate.
  • the coloured dye will be formed inside the anodic film.
  • MAGOXIDTM process is disclosed in US Patent 4,978,432.
  • TAGNITETM is described in the Society of Automotive Engineers (SAE) Aerospace specification AMS#2467 and US Patent 5,470,664.
  • TAGNITETM is a "spark" anodisation process characterised by the presence of plasma discharges all over the surface of the part during the process.
  • MAGOXIDTM is intended to produce a layer comprising magnesium aluminate and magnesium phosphate, using a pulsed or AC current to achieve cationic presence near the substrate surface. It is described in US Patent 4,978,432 and has been referred to herein above.
  • DOW 17TM is an acid fluoride based anodisation process that produces an intrinsic green film whose colour intensity depends on the end point voltage of the process. In some cases it may be very dark. Clearly the reason why such a film would be coloured would not normally be to produce a range of colours as the intrinsic substrate colour limits this, but to benefit from the improved conosion resistance imparted by colouring. DOW 17TM colours well in these dyes although its intrinsic colour limits the range of shades obtainable.
  • HAETM is an alkaline anodising process using an alkali hydroxide, potassium fluoride, trisodium phosphate and potassium manganate in solution. It produces varying shades of brown coating which is not intrinsically amenable to taking a colour, but which may be coloured using the dyes described herein to take advantage of the improvements in salt spray corrosion resistance obtained in doing this.
  • the reactive dyes will selectively split a secondary hydroxyl group in a cellulose molecule, as pictured below:
  • a direct black dye was used to colour a 10 micron anodic film on magnesium alloy AZ91D: a 0.5% solution of Ciba-Geigy's Solophenyl®Direct Black GN dye was prepared and heated to 60 ° C. 0.5% sodium sulphate by weight was added and an anodic voltage of 10 volts was applied to the article. After 30 minutes the article was found to be a deep black in colour.
  • a strip of hot rolled anodized AZ31 magnesium alloy, having an anodic film of 15 ⁇ m was introduced to a dye bath containing a monochloro triazine reactive blue dye which was freshly prepared.
  • the bath contained:
  • Example 4 A die casting composed of AZ91D magnesium alloy was coloured black using
  • Cl Leuco Sulphur Dye Black 1 a liquid dispersion of sulphur dye.
  • the sulphur dye was converted to the soluble leuco form by adding a proprietary reducing agent, Reducer NS and salt as follows: (a) Cl Leuco Sulphur Dye Black 1 - 8% (b) Reducer NS - 8%
  • the solution was heated to 90 °C and the magnesium article introduced to the bath for thirty minutes after which it had an even flat black appearance. Finishing comprised a rinse in hot water then an oxidising bath comprising hydrogen peroxide, 0.5%) and sodium perborate 10 grams per litre. This bath was heated to 40 °C. After this treatment, the article was dried and when dry, had a uniform flat black appearance.
  • a die cast component comprising AZ91D magnesium alloy was coloured in a vat black dye using sodium dithionite as a reducing agent and sodium hydroxide as an alkali.
  • the leuco dye was prepared in the following manner:
  • a stock vat dye dispersion was prepared from 100 grams per litre vat dye and 250ml per litre 10 molar sodium hydroxide solution. To this was added 100 grams per litre of sodium dithionite to solubilise the dye, converting the dispersion to the water soluble enol salt form.
  • a strip of hot rolled AZ31 magnesium alloy was introduced to a suspension of a disperse dye, Cl Disperse Red 1 to which had been added 0.1 % Pecar® GL, a proprietary carbonyl acid ester carrier compound.
  • the dye bath was heated to boiling point and maintained for 30 minutes after which time the magnesium article was found to be a pastel orange-pink colour.
  • a number of magnesium alloy AZ91D test plates were anodised to a nominal film thickness of 20 microns using the process described in PCT/NZ96/00016. A number of these were coloured using several different vinyl sulphone reactive dyes, whereas the remainder were not coloured.
  • ASTM Bl 17 The samples were evaluated according to the two part method described in ASTM D 1654. Under part B of this method, which deals with general corrosion, the samples which were not coloured failed after about 500 hours, whereas those which were coloured were in most cases still passing after 1,034 hours.
  • a tube composed of Melram® 072 TS alloy (magnesium containing 12% silicon carbide in a mixed metal composite) was anodised by the procedure described in PCT/NZ96/00016 to a thickness of about 5 ⁇ m. This was then coloured yellow using a vinyl sulphone reactive dye, Eversol® Yellow, at 60°C for 30 minutes, at a concentration of 0.5% with a concentration of 0.5% sodium carbonate and 0.25% sodium hydroxide. The result was a bright yellow-gold colour.
  • Example 10 A sample of hot rolled magnesium alloy AZ31 sheet was anodised to a thickness of 15 ⁇ m and coloured using a vinyl sulphone reactive dye, Eversol® Blue, at a concentration of 0.5%, together with 0.5%> sodium carbonate and 1 % sodium hydroxide, yielding a dark blue colouration of the sample.
  • a vinyl sulphone reactive dye Eversol® Blue

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  • Chemical & Material Sciences (AREA)
  • Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Electrochemistry (AREA)
  • Materials Engineering (AREA)
  • Metallurgy (AREA)
  • Organic Chemistry (AREA)
  • Electrolytic Production Of Non-Metals, Compounds, Apparatuses Therefor (AREA)
  • Coloring (AREA)
  • Powder Metallurgy (AREA)
  • Electroplating Methods And Accessories (AREA)
  • Chemical Treatment Of Metals (AREA)
EP98914164A 1997-03-24 1998-03-23 Mit magnesium kolorierte oder aus magnesium-legierung bestehende gegenstände Withdrawn EP1015670A4 (de)

Applications Claiming Priority (7)

Application Number Priority Date Filing Date Title
NZ31446797 1997-03-24
NZ31446797 1997-03-24
NZ32831697 1997-07-11
NZ32831697 1997-07-11
NZ32871997 1997-09-11
NZ32871997 1997-09-11
PCT/NZ1998/000039 WO1998042895A1 (en) 1997-03-24 1998-03-23 Colouring magnesium or magnesium alloy articles

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WO2002028838A2 (en) * 2000-10-05 2002-04-11 Magnesium Technology Limited Magnesium anodisation system and methods
NZ510922A (en) * 2001-04-03 2003-09-26 Ind Res Ltd Anodising magnesium and magnesium alloy components with an aqueous electrolyte solution which comprises a phosphate which is not a monophosphate
ES2344015T3 (es) * 2001-06-28 2010-08-16 Alonim Holding Agricultural Cooperative Society Ltd. Tratamiento de una superficie para mejorar la resistencia a la corrosion de magnesio.
GB2395491B (en) * 2001-08-14 2006-03-01 Magnesium Technology Ltd Magnesium anodisation system and methods
JP2003160898A (ja) 2001-09-17 2003-06-06 Fujitsu Ltd マグネシウム材の着色方法およびこれにより着色されたマグネシウム材製筐体
US7569132B2 (en) 2001-10-02 2009-08-04 Henkel Kgaa Process for anodically coating an aluminum substrate with ceramic oxides prior to polytetrafluoroethylene or silicone coating
US7452454B2 (en) 2001-10-02 2008-11-18 Henkel Kgaa Anodized coating over aluminum and aluminum alloy coated substrates
US6916414B2 (en) 2001-10-02 2005-07-12 Henkel Kommanditgesellschaft Auf Aktien Light metal anodization
US7578921B2 (en) 2001-10-02 2009-08-25 Henkel Kgaa Process for anodically coating aluminum and/or titanium with ceramic oxides
AU2003213340A1 (en) * 2002-03-25 2003-10-08 Hori Metal Finishing Ind. Ltd. Magnesium or magnesium alloy article having electroconductive anodic oxidation coating on the surface thereof and method for production thereof
JP2008216058A (ja) * 2007-03-05 2008-09-18 Kobe Steel Ltd マグネシウム含有材の表面検査方法
US9701177B2 (en) 2009-04-02 2017-07-11 Henkel Ag & Co. Kgaa Ceramic coated automotive heat exchanger components
JPWO2014203919A1 (ja) * 2013-06-19 2017-02-23 堀金属表面処理工業株式会社 マグネシウム合金製品の製造方法
EP3368706A4 (de) 2015-10-27 2019-05-01 Métal Protection Lenoli Inc. Elektrolyseverfahren und -vorrichtung zur oberflächenbehandlung von eisenfreien metallen
CN105714354A (zh) * 2016-03-21 2016-06-29 南京工程学院 一种用于制备n掺杂微弧氧化陶瓷层的电解液
KR20200089698A (ko) 2017-11-17 2020-07-27 토아덴카 코., 엘티디. 흑색 산화 피막을 구비하는 마그네슘 또는 알루미늄 금속 부재 및 그의 제조 방법
CN108914191B (zh) * 2018-08-15 2020-06-26 西安理工大学 镁合金表面制备高吸收黑色陶瓷层的自然着色方法

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US4620904A (en) * 1985-10-25 1986-11-04 Otto Kozak Method of coating articles of magnesium and an electrolytic bath therefor
DE3808609A1 (de) * 1988-03-15 1989-09-28 Electro Chem Eng Gmbh Verfahren zur erzeugung von korrosions- und verschleissbestaendigen schutzschichten auf magnesium und magnesiumlegierungen
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WO1998042892A1 (en) 1998-10-01
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EP1015661A1 (de) 2000-07-05
IL131996A (en) 2003-04-10
DE19882231T1 (de) 2000-02-10
IL131996A0 (en) 2001-03-19
GB2341397A (en) 2000-03-15
EP1015661A4 (de) 2000-11-02
CA2284616A1 (en) 1998-10-01
GB9922584D0 (en) 1999-11-24
EP1015670A4 (de) 2002-01-02
JP2002515092A (ja) 2002-05-21
AU6858198A (en) 1998-10-20

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