CA1070636A - Method of forming a coloured anodic oxide film on aluminum based-alloy material - Google Patents

Abstract

METHOD OF FORMING A COLOURED ANODIC OXIDE
FILM ON ALUMINUM-BASED ALLOY MATERIAL

ABSTRACT OF THE DISCLOSURES
Method of forming a coloured anodic oxide film on the surface of an aluminum-based alloy material comprising the steps of subjecting the material having an oxide film thereon to colouring electrolytic treatment in a bath of an electrolyte containing a water-soluble nickel salt and boric acid. The material is placed in the bath through which a pulsating al-ternating electric current having a negative pulse duration which is the same as or greater than that of the positive voltage pulse.

Description

1~)7~636 .
The present lnventlon relate~ to a method of forming a coloured anodic oxide coating on the ~ur~ace of aluminum or an alumlnum-based alloy meterlal.
It 1~ known that coloured anodic oxlde fllms can be form-`5 od on the surface ~f aluminum or an alumlnum alloy (hereinafter ~, , -~ roforrod to a~ aluminum-ba~ed metal) by first anodlzlng the aluminum-ba~ed metal to produce an anodically oxldized film , . . .
~ thoroon and then subJectlng lt to an electrolytlc process ln ~, . .--~hich the anodlzed metal i~ placed ln a bath of an eloctrolyte contalning a metal Jalt. In thls electrolytlc proce~s, tho nodlzed metal and metal~ serve as an anode or as both of an .,, ~ . ;
anode and a cathode. Consequently, the anodlc oxlde fllm on the ~ur~ace o~ the metal i8 provlded wlth a colour ln accordance ~ .~
~lth the type o~ the metal salt contalned ln the bath.
~15 For example, Unlted State~ Patent No. 3,382,160 to T.
A~ada di~close~that an anodic oxlde fi~lm produced on the ~urface of an alumlnum-ba~ed metal 1~ coloured by sub~ectlng .. , ~ . .. .
tho anodlzed aluminum-based metal to an electrolytlc proce~s ln whlch an alternatlng current 18 passed through an acldlc bath -~ 20 contalnlng a metal lon ~uch a-q nlckel, cobalt, chromlum, copper or cadmium lons. Unlted States Patent No. 3,669,856 to O.C.
Gedde dlscloses that a colour of an anodized fllm can be easlly controll-d by suO~ectlng the anodized fllm to an alternatlng current wlth an asymmetrlc voltage pattern ln an anodic bath contalnlng metal ion~.
In these electrolytlc colouring processes, it has been thought that the anodic oxlde rllms may be coloured wlth the etal~lonJ whlch are flrst depo~lted on the walls of pores ln the anodlc oxlde ~llms when the negatlve voltage i8 applied and thon~dl~solved there~rom when the positlve voltage is applled.
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It 18 known that tho colour~ thus produced on the anodlc oxide rllms may depend on the location~ and amo ~ of the metal ions dissolvlng from the pores of the films. These conventional - processe~ cannot provide a positlve control of such locatlons ;-~ 5 and amountJ Or the metal lons disJolvlng rrom the pores of the ; rilms. Control therefor i8 carried out by ad~ustlng the bath temperatur~ and the processlng time in accordance with a desired ~-amount of the metal lons to be dissolved. However, the ad~ust-.: ment is not sati~factorr to provide uniform colours on the apo-~10 dized oxide layera. Particularly, it ha~ been found thereinthat e~en ~ery small ~arlations in the processing time may ai?i~ect tho colour~ o~ the S~lm~. For example, even ~light changes~, .
- ~ though sometlmea unavoidable, in the bath temperature and the proce8sing time ln a single bath may provlde the anodlc oxide . .
!~.... 15 rllm wlth coloura lncluding from a brlght amber color to a dark ; ~ blacklsh bronze colour.
It 1~ therefore an ob~ect of the present inventlon to pro-vlde a process oS produclng coloured anodic oxlde films on p!,,~
~lu~inum-based metals wlth minimum variations ln colour.
Another ob~ect o~ the present invention is to provide a process of applylng colours to anodic oxido fllm~ on aluminum-.
ba~ea ~et d~ in a bath of electrolyte havlng a given composition.
~ A further ob~ect Or the present lnvention i~ to provlde a ;~ proceJs of producing coloured anodlc oxide films on aluminum-based metals by applylng alternatlng voltage pulses having negative pulffo duration longer than po~itlve pulse duration to tho metals in a bath of el~ctrolyte containing a water-soluble ~ lckel salt and borlc acid.
''~ . " ` ! ~ me method of-producing coloured anodic oxlde films on ~ 30 ~ alumlnum-based metals ac¢ordlng to tho present inventlon compri~es .... ~ ~ .
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~' ~- the steps of producing anodlc oxide films on the metals, lm-mersing the metals in a bath of electrolyte containlng a water-- oolublo nickel salt and boric acid and applying to the metal~
--~ alternatlng voltage pulse~ having negative pulse duration whlch ~- 5` 1~ at least the aame as or longer than positive pulse duration.
- According to th~ method of the present invention, it may ~; bo noted that boric acid contained in thc electrolyte may ~erve .
- ~ ao produclng a complex of a water-soluble nickel salt and boric ~` acld ln the viclnlty of the previou~ly formed anodic films and ~0 ~ that the actlve sites of pores in the anodic oxide film may be oaturated with the metallic ions as coloring factors for a short :, .
i ~ perlod because of the action of high level energy at the ris~ng and decreaolng periods o~ each pulse on the aluminum-bas~ed metal, thcreby keeping the metallic lons from dissplution after a predetermined period of tlm~ ~or electr~lyJis and consequently prorlding a uniform color.
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~ ~ The process of the present invention is carried out as fol-~ . ~
~ lowo. An aluminum-baqed material to be colored i8 first provided . ~ :
~ wlth an anodlc fllm accordlng to conventional anodizlng treat-. ~ - , . ; ~ . .
;~ 20- mont.
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~ The anodized material ls then dlpped into a bath of electro-,. . . .
lyto containing borlc acid and a water-baluble nickel salt. In ; ~ thls procels, the anodized material or materials serve as one or both Or electrodes, The bath~contain from about 10 to 50 grams ~25 of boric acid per liter of water. Preferably, the boric acid may be di~sol~ed ~p to its upper linit. me amount of the water-ooluble nickel salt may be from about 15 to 150 grams per liter ;~ of water. Preferred examples of the water-~oluble nickel salts aro nickel acetate, nickol sulfate and nickel chloride; other -~ 3~ nickol oalto ~ay bo used as long ao they aro ooluble in water.
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, 10~0636 e aluminum-based material 1s placed in a bath through whlch a pulsating altornating current is passed, the current h~lng negatl~e pul~e voltago greater than the posltive one and ha~lng longer duratlon than that of tho positlve pul~e voltage.
~: - 5 me voltage thus applied to the material may comprise al-` t~rnating po~iti~e and noatlvo pulses or a plurallty of positi~e pulse~ which are followed by a plurality of negative pulses.
Pul8~ting voltages of any wave rorm may be used as long as they c n apply ~lgh le~el energy to the materials to be treated.
- lO According to the prosent lnventionj the anodlc oxide fllm ~ ,:
-~ on the materlal is glven with bronze based colours which are ; lnherent to nlckel ions and which may be selected ln the range lncluding relati~ely bright amber through relatively dark blackish colour ~imply by determining the values of the al-lS ternating voltage pui9es. It i8 posslble to provlde a substantial-ly unifor color on the anodic oxlde fllms over a wlde range ; evon ~fter the treatment waJ ptrformed beyond a certaln requlred ~. .
time. There may be substantially no colour varlatlons ln ac-oordance with a change ln proco~lng time and/or temperature.
~; :. ;: 20 : Examples An alu~minum-based alloy (llOO) was flrst subJected to a con~entlonal anodizing process to form thereon an oxlde film.
Then, the material is dlpped ln a bath Or colouring electrolyte .: ~. ; . .
containing SO grams of boric acid and lOO grams of (CH3C00)2-Ni4H20 per liter of water. Thereafter, a colouring electrolytic proce~ was performed by applying to the materlal for ~ to lO
minutes such voltage pulses that comprise aiternating po~itive and negativo pulses. me bath wa~ maintained at a temperature of 20 to 22C. me results are shown ln Table l wherein the 30~ chur~oter~ X, Y and Z designate Munsell notations.

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It ~111 be noted i~rom Table 1 that an amber-like colour can be produced by applying to the material alternatlng voltage - pulse~ comprislng alteraatlng negatlve voltage pulses of 13 ~ volt~ and 3 second duration and positlve voltage pulses of 13 `,~,~ 5 ` volt~ and l aecond duration. As far as the treatment was per-for~od iPor at least 7 mlnute~, the proce~slng tlme did not have -,` any ei?~ect on the colour.
An alumlnu~-based alloy member~ having anodic oxide films were dlpped a~ the electrode~ ln a bath of electrolyte having '"`''~;10~ a composltlon a~ Jhown in Table 2 and havlng a bath temperature ' ;'` ' ,o~ 20 to 22VC. Alternating voltage pulses were then passed bst-,' ; ween the members for i?lve mlnute~. The alternatlng voltage -''' ';~ pul~eJ comprl~ed negative pulses o~ 12,5 volts Or average voltage ' and duratlon o~ 3 ~oconds, and posltlve pulses of 5.5 volts Or -~"~-15 a~erage voltage~nad,~duratlon of l seco~d. me results are ~hown ~' ln Table 2. me M~nsell notation~ in Tablo 2 are average values o~ those obtained upon several experiments. Visual observations , proved very llttle variatlons ln coloùr particularly wlth the bath containlng 100 g/l Or nickel salt and 50 g/l of boric acid.
~ me lnvention ha~ thus been shown and described with refe-' renoe to ~pecific example~ however, it ~hould be noted that the !; ",~ i m entlon is no way llmited to the detalls of the described ex-, ample~ but changes and modirications may,be made without depart- ' g rrc- the ~Cop- Or the appended clalma.

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;-- ~ 20 ~ 4 . 4 3 . 7 4 . 4 . 10 35 3 . 5 2 . 8 3 . 8 . `.i~: _ 50 ~ 3 . 3 2 . 9 3 . 6 ,......... ~ __ . ~ .
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Claims (5)

The embodiments of the invention in which an exclusive property or privilege is claimed are defined as follows:

1. A method for producing coloured oxide films comprising subjecting an aluminum based material to an anodizing treatment to produce an oxide film thereon, dipping the material in an electrolyte bath containing from about 70 to about 150 grams of a water-soluble nickel salt per liter of water and from about 20 to about 50 grams of boric acid per liter of water, wherein the bath is maintained at a temperature between about 20° and about 22°C, and applying alternating voltage pulses to the aluminum based material, the alternating voltage pulses including more than one negative voltage pulse and more than one positive voltage pulse, and wherein the negative voltage pulses have a duration which is at least the same as that of the positive voltage pulses, the negative voltage pulses have a range of from about 12.5 to about 15 volts, and the positive voltage pulses have a range of from about 5.5 to about 13 volts.

2. The method in accordance with claim 1 wherein the water-soluble nickel salt is selected from the group consisting of nickel acetate, nickel sulfate and nickel chloride.

3. The method in accordance with claim 2 wherein the water-soluble nickel salt is nickel sulfate.

4. The method in accordance with claim 1 wherein the bath contains from about 100 to about 150 grams of nickel salt per liter of water.

5. The method in accordance with claim 1 wherein the positive voltage pulses are applied in durations of from about 1 to about 3 seconds.