Classifications

• • C—CHEMISTRY; METALLURGY
  • C25—ELECTROLYTIC OR ELECTROPHORETIC PROCESSES; APPARATUS THEREFOR
  • C25D—PROCESSES FOR THE ELECTROLYTIC OR ELECTROPHORETIC PRODUCTION OF COATINGS; ELECTROFORMING; APPARATUS THEREFOR
  • C25D9/00—Electrolytic coating other than with metals
  • C25D9/04—Electrolytic coating other than with metals with inorganic materials
  • C25D9/06—Electrolytic coating other than with metals with inorganic materials by anodic processes
• • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
  • Y10S—TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
  • Y10S524/00—Synthetic resins or natural rubbers -- part of the class 520 series
  • Y10S524/901—Electrodepositable compositions

Definitions

• This invention relates to improved means of coating metal or otherconductive surfaces by electrodeposition. It is well known that a film of aluminium oxide may be formed electrolytically on an aluminium surface by anodic oxidation, and that such a film has a protective value in itself, while it forms a basis for the adhesion of a subsequently applied film of lacquer or other coating material. A further distinctive property of the alumina film is that when freshly formed it is capable of being coloured by suitable dyestuffs, so that pleasing decorative finishes may be obtained.
• conductive surfaces without restriction to aluminium, may be coated with a film consisting of or containing aluminium oxide, by making such a surface the cathode in electrolysis of an aqueous solution containing basic aluminium salts, and a process of this kind has been proposed for obtaining insulating coatings on copper conductors.
• the constituent of the electrolyte which contains aluminium is associated with a positive electric charge.
• alumina is deposited on the'conductive surface as anode, by use of an aqueous medium such that the constituent containing aluminium is associated with a negative electric charge.
• This has the advang9 tage that other effects can also be obtained on themetal surface very readily, as hereafter explained.
• a solution containing an aluminate for example sodium aluminate, in which aluminium occurs in the form of a negatively charged ion (or anion)
• under suitableconditions the passage of an electric current results in the precipitation on the anode of a film consisting of or containing 40 aluminium oxide or hydroxide.
• This film may be washed and dried, when it may be coated if desired with a lacquer or other material, for which it affords an excellent basis, or it may be dyed (preferably beforedrying), in the wellknown manner of anodically oxidised aluminium.
• a valuable application of this invention is to the coating of metals such as' tinplate, which are used to make containers for foods'tuffs,.as the non-toxic character of aluminium 'oxide makes it 5i) a suitable. compound either for direct contact with the foodstuff, in cases where a lacquer is unnecessary, or as a basis for application of a lacquer where this is desirable.
• the anodic deposition of alumina has in the case 'of tinplate as the advantage that flnodlc oxidation ofthe tin surface occurs at the same time, and we have already disclosed in our U. S. Patent application Serial No. 146,691 filed June 5, 1937, that anodically oxidised tinplate is resistant to discolouration bysulphur-bearing foodstuffs.
• Our experi- 6 ments have shown that the additional cover provided by an aluminous'film is a useful supplement in that the resistance to discolouration is increased.
• a further application of the invention which 10 again is of interest in connection with tinplate, is the use of dyed alumina films for producing decorative external coatings, comparable with those obtained from anodically oxidised aluminium.
• Deposition of the aluminous film at the anode has an important advantage in that we have found it possible to emulsify or disperse in the alkaline solution substances such as lacquers or waxy materials, and passage of an electric current then results in the simultaneous deposition of an aluminous compound and of the dispersed material, so that composite coatings may be obtained in a single operation.
• the effect of gas evolution may be reduced by adjusting the alkalinity of the solution to such a value that aluminium oxide or hydroxide is 40 only just held in solution in absence of electrolysis. Deposition then occurs at a low current density, at which gas evolution is relatively small.
• Reduction of the alkalinity may be effected by addition to the solution of an acid, or of a salt having a reaction more acid than sodium aluminate containing alumina only just held in solution, with the limitation that the anion of the added acid or salt should not form with the metal of the' electrodea soluble salt or a bulky precip- 5o itate which might interfere with the formation of a coherent alumina film.
• hydrochloric acid is not suitable.
• the anion of the added acid -or salt is such as will cause any film formed by direct anodic attack as on the metal, as apart from decomposition of the aluminate, to be compact and adherent.
• Suitable compounds for use with tinplate are, for' example, sodium bicarbonate or sodium dihydrogen phosphate.
• the aluminous film arises from decomposition of the aluminate ions as a result of changes in the composition of the electrolyte in the vicinity of the anode during electrolysis, and the invention is therefore not limited to the use of a particular metal or other conductive surface as anode.
• tinplate is mentioned as an illustration of an application of the invention to the art of tin box making, but no restriction on the field of the invention is thereby implied.
• sodium bicarbonate solution is gradually added to a solution of sodium aluminate in amount just insufficient to cause precipitation' of aluminium oxide or hydroxide in the absence of electrclysis, or addition may be continued until precipitation just sets in, the solution being then filtered, and further diluted if desired.
• This de-stabilised solution may be used without addition of a depolarizing agent.
• sodium bisulphite maybe used instead of sodium bicarbonate in the above preparation, in which case the sodium bisulphite itself provides a depolarizing agent as well as adjusting the alkalinity. If additional depolarizer is desired, excess of'sodium bisulphite may be used, and caustic soda then added so as just to redissolve the precipitate.
• the solution contains also colloidal material, or a substance or substances capable of giving rise to colloidal material, such as will migrate towards the anode during electrolysis.
• colloidal material or a substance or substances capable of giving rise to colloidal material, such as will migrate towards the anode during electrolysis.
• the dry film may be superficially somewhat powdery when an aluminate is used without colloidal material, whereas under the same conditions a smooth coherent film is obtained when colloidal material is present.
• a 2 per cent. solution of sodium aluminate may be destabilised with sodium bicarbonate as already described, and gelatin dissolved in a small amount of water may be added, the solution being then diluted to bring-the concentration of sodium aluminate to 1 per cent.
• the concentration of gelatin in the final solution may be of the order per cent.
• a smooth, opalescent thin film may be obtained on tinplate by electrolysis for 612 seconds at a current density of 2 to 4 amps. per square foot.
• Tinplate or tinplate containers may be coated with a smooth, coherent film of opaque appearance by electrolysis for 10 seconds at a. current density of 10 amps. per square foot.
• thedeposited film may undergo further treatment, preferably after washing but before drying.
• further treatment preferably after washing but before drying.
• a tinplate can be coated internally with an aluminous film by anodic deposition as de-,'
• the latter may be treated with an emulsion of lacquer dispersed in dilute ammonia. Under such conditions a certain amount of thelacquer becomes fixed to the surface and is not removable by washing, and it may be stoved in the usual way.
• the surface may be further coated with lacquer by electrodeposition from a lacquer-inwater emulsion, the aluminous deposit being a conductor while still wet.
• the dried film may be coated with lacquer, wax, cellulose or other materials from solutions in organic solvents or by other means.
• composite coatings may be obtained on the anode by use of an aqueous medium containing an alkalimetal aluminate in solution and a lacquer or waxy material in dispersion.
• alumina which term is used to describe any aluminium compounds in the deposit, their exactnature be-' ing unknown
• the simultaneous deposition of alumina greatly improves the characteristics of an electrodeposited lacquer or similar film even when the proportion of alumina is not large.
• the deposit is more water repellent before drying, so that it may be freed of emulsion.
• Tinplate cans internally lacquered by this method after fabrication have been found to be almost entirely free from discontinuities in the lacquer coating.
• coatings may be obtained which after stoving are pale, matt and substantially opaque, or which are deep in colour, bright and substantially transparent, or coatings may be obtained having intermediate characteristics in respect of colour,
• the depth of colour and brightness may be enhanced by diminishing the concentration of aluminate.v
• lacquer acids are in general contributed partly by the drying oil and partly by the resin, and we have found that diiferent results are obtainable according as the oil is kept constant and the type of resin is varied or the resin is kept constant andthekind of oil is varied, in each case without alteration of the ratio of resin to oil, or alternatively, without significant alteration of the acid value of the lacquer as a whole.
• Lacquer G Linseed stand o'L 175 (Coumarone resi 100- Estimated acid value: 6-7.
• lacquer B was lacquer Awith its acid value increased by addition of rosin,-a nearly completely saponifiable resin.
• Lacquers C and D were identical in resin/oil ratio and both contained the same kinds of acids, but with diflerent proportions of resin acids.
• Lacquers E and F had practically the same acid values as C and 1), respectively, but the resin used was different.
• Lacquers G and H had both low acid values and contained the same ratio of oil to resin, but in the former case the acidity was derived almost entirely from the oil and in the latter case almost entirely from the resin.
• each lacquer was mixed with a thinner in the ratio parts of lacquer to 1 part of thinner.
• the thinner consisted of 85 per cent (by weight) white spirit and 15% turpentine.
• emulsions were made of 1, 2 and 3. parts respectively of thinned lacquer in 4 parts of 1 per cent sodium aluminate solution, and in the 'case of the less acid lacquers, also of 4 parts of lacquer in 4 parts of solution.
• the character of the film may be modified by variations in the composition of
• the effect of reducing the concentration of sodium aluminate has already been mentioned.
• free alkali such as sodium hydroxide or ammonia
• An alternative method of obtaining a similar result is by emulsification in a solution containing sodium silicate in addition to sodium aluminate.
• a solution containing sodium silicate in addition to sodium aluminate.
• a mixture of 75 partsof 1 per cent sodium aluminate solution and 125 parts of a solution containing 1 per cent (as solid) of sodium silicate having a NaaO, SiOa ratio of 1:3.8 may be used.
• the brightness of the finish may be increased by including in the aqueous phase an emulsifying agent of the same type as is obtained by saponification of the lacquer acids.
• emulsions were made of 100 parts of lacquer A in 200 parts of a solution containing 1 per cent of sodium aluminate and 9i and per cent respectively of rosin soap. With increase in rosin soap content the films were progressively brighter and also progressively paler.
• the brightness (for a given depth of colour), depends on the proportions of alumina present in the film, whereas the depth of colour (for a given lacquer stoved under constant conditions) increases with the Weight of the film.
• the weight of the film may be increased by suitable alteration in the electrical treatment, for example by an increase in initial current density, in the duration of treatment or by decrease in the rate of decline of the current.
• a lacquer composition and concentration such that a desired type of coating may be obtained from an emulsion in a given aqueous phase, or alternatively when the lacquer is given it is possible by choosing the aqueous phase and lacquer concentration suitably to modify the ratio of alumina to lacquer in the coating.
• alumina is used in connection with these composite coatings that this is for descriptive purposes, and does not imlacquer
• waxy materials may be dispersed in so-- lutions containing aluminates either alone or in conjunction with other materials, and that coherent deposits are then obtained more readily by electrodeposltion than when such substances are not present.
• wax or lacquer in liquid form as used in the claims, it is meant wax or lacquer dispersed in solution or dissolved in organic solvent.
• a method of coating a conductive surface which consists in making said surface the anode,
• a method of coating a conductive surface which consists in making said surface the anode in an' aqueous solution containing a soluble aluminate, and also a polarizing reducing agent and passing an electric current through said solution whereby an aluminous compound is deposited as a film on said surface.
• a method of coating a conductive surface which consists in making said surface the anode in an aqueous solution containing a soluble aluminate and sodium bisulphite, and passing an electric current through said solution, whereby an aluminous compound is deposited as a film on said surface.
• a method of coating a conductive surface which consists in electrcdepositing an aluminous compound on the said surface as anode in an aqueous solution containing a soluble alumlnate and a depolarizing reducing agent and a coating selected from the group consisting of lacquer and wax by electrodeposition from an aqueous dispersion.
• a method of coating a conductive surface which consists in electrodepositing an aluminous compound on the said surface as anode in an aqueous solution containing a soluble aluminate and a depolarizing reducing agent and a coating selected from the group consisting of lacquer and wax by application in liquid form.
• a method of' coating a conductive surface which consists in making said surface the anode in an aqueous medium containing an alkali metal aluminate and also lacquer indispersion and passing an electric current through said medium, whereby an aluminous compound and lacquer are dep'osited'together as a film on said surface.

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• Chemical & Material Sciences (AREA)
• Inorganic Chemistry (AREA)
• Engineering & Computer Science (AREA)
• Chemical Kinetics & Catalysis (AREA)
• Electrochemistry (AREA)
• Materials Engineering (AREA)
• Metallurgy (AREA)
• Organic Chemistry (AREA)
• Electrolytic Production Of Metals (AREA)
• Paints Or Removers (AREA)

Applications Claiming Priority (1)

Publications (1)

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ID=9862737

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Cited By (9)

Families Citing this family (1)

• 0
  • BE BE427261D patent/BE427261A/xx unknown
• 1937
  • 1937-03-30 GB GB8966/37A patent/GB492900A/en not_active Expired
• 1938
  • 1938-03-29 US US198682A patent/US2215167A/en not_active Expired - Lifetime
  • 1938-03-30 FR FR836803D patent/FR836803A/fr not_active Expired

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