U.S. patent number RE29,739 [Application Number 05/765,451] was granted by the patent office on 1978-08-22 for process for forming an anodic oxide coating on metals.
This patent grant is currently assigned to Joseph W. Aidlin. Invention is credited to Saul Kessler.
United States Patent |
RE29,739 |
Kessler |
August 22, 1978 |
Process for forming an anodic oxide coating on metals
Abstract
Efficiency of chemical surface finishing baths for metal
articles, particularly electrolytic baths for anodizing metals such
as aluminum, magnesium or titanium is improved by incorporating
into the bath an effective amount, typically from 0.1 to 50 grams
per liter of the reaction product of a metal halide, such as boron
trifluoride, and a trifluoro-alkaryl amine, suitably
.alpha.,.alpha.,.alpha.-trifluoro-m-toluidine.
Inventors: |
Kessler; Saul (Canoga Park,
CA) |
Assignee: |
Aidlin; Joseph W. (Los Angeles,
CA)
|
Family
ID: |
24430937 |
Appl.
No.: |
05/765,451 |
Filed: |
February 3, 1977 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
Issue Date |
|
Reissue of: |
607127 |
Aug 25, 1975 |
03996115 |
Dec 7, 1976 |
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Current U.S.
Class: |
205/332; 205/316;
205/320; 205/321; 205/322; 205/331 |
Current CPC
Class: |
C23C
22/00 (20130101); C25D 11/06 (20130101); C25D
11/26 (20130101); C25D 11/30 (20130101); C25D
11/34 (20130101) |
Current International
Class: |
C23C
22/00 (20060101); C25D 11/02 (20060101); C25D
11/26 (20060101); C25D 11/30 (20060101); C25D
11/04 (20060101); C25D 11/34 (20060101); C25D
11/06 (20060101); C25D 011/34 (); C25D 011/26 ();
C25D 011/30 () |
Field of
Search: |
;204/56R,56M,58 |
References Cited
[Referenced By]
U.S. Patent Documents
Primary Examiner: Andrews; R. L.
Attorney, Agent or Firm: Jacobs; Marvin E.
Claims
What is claimed is:
1. A method of depositing an electrolytic anodic oxide layer on the
surface of a metal article capable of being converted to a
passivated metal salt layer comprising the steps of:
applying to the surface of the article an aqueous anodizing
electrolyte containing an effective amount of oxidant capable of
forming an anodic oxide on the metal surface and 0.1 to 50 g/l of
an additive comprising the reaction product of (a) a halogenated
compound of fluorine, chlorine, iodine or bromine and an inorganic
cation selected from Groups 1b, 2, 3a, 4b, 5b, 6b or 8 and (b) an
alkarylamine of the formula: ##STR2## where n is an integer from
.[.1.]. .Iadd.0 .Iaddend.to 4, m is an integer from 1-2 and R is
selected from hydrogen, lower alkyl of 1-9 carbon atoms, lower
alkanol of 1-8 carbon atoms, aryl or aralkyl and Z is .[.hydrogen
or.]. CX.sub.3 where X is fluoro, chloro, bromo, .Iadd.or
.Iaddend.iodo .[.or R.].:
making the article the anode in the electrolyte;
applying a current density between 5 to 200 amps/dm.sup.2 ; and
depositing an anodic oxide layer on said surface.
2. A method according to claim 1 in which the inorganic cation is
selected from copper, magnesium, boron, aluminum, chromium or
tungsten.
3. A method according to claim 2 in which the halogenated compound
and amine are present in the additive in an amount from 1 to 20
parts by volume of amine to 1-20 parts by volume of compound.
4. A method according to claim 2 in which the trihalogenated
compound is boron trifluoride etherate.
5. A method according to claim 4 in which the amine is a
fluoro-alkarylamine.
6. A method according to claim 5 in which the fluoro-alkarylamine
is .alpha.,.alpha.,.alpha.-trifluoro-m-toluidine.
7. A method according to claim 4 in which the amine and compound
are present in the additive in an amount from 2 to 5 parts of amine
by volume to 2 to 5 parts of compound by volume.
8. A method according to claim 1 in which the metal article being
treated comprises a metal selected from aluminum, titanium,
magnesium, copper, iron or alloys thereof.
9. A method according to claim 8 in which the metal article
comprises aluminum and the oxidant is an electrolytic aluminum
anodizing electrolyte.
10. A method according to claim 9 further including the steps of
cooling the bath to a temperature from -20.degree. C to 20.degree.
C.
11. A method according to claim 10 in which the electrolyte is
sulfuric acid present in an amount from 5 to 400 grams per liter,
the additive is present in an amount from 0.1 to 20 grams per
liter, and the current density applied to the bath is from 5 to 200
amps/dm.sup.2.
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to chemical surface coating or
etching of metals, and more particularly, to improved baths for
electrolytic anodizing of metals, particularly light metals such as
aluminum, magnesium or titanium.
2. Description of the Prior Art
The surface layer of metal articles are chemically converted to
oxide or salt forms such as phosphate and or chromate to protect
the metal from wear, corrosion or erosion or to act as an
undercoating or base layer for organic finishes. Electroless
chemical oxide conversion coatings are very thin and soft. While
they are adequate in many cases as a protection against mild
corrosion, they are normally not suitable if additionally they have
to resist more severe corrosion as well as wear and abrasion.
Phosphate and chromate chemical conversion coatings have the
advantage of economy and speed and involve relatively simple
equipment and do not require electrical power. Adequate corrosion
resistance and useful paint adhesion characteristics are imparted
to the surface which are entirely sufficient for many applications.
These finishes are also used as temporary protective measures on
aluminum articles which may require storage for an appreciable
period before use.
In the case of aluminum, the chemical oxide conversion coating is
thicker than the natural oxide film which forms when a freshly cut
aluminum surface is exposed to the atmosphere. However, the
conversion coating is still considerably thinner than the oxide
films produced by anodizing and is not suitable for applications
requiring hard, dense, thick coatings.
Of the numerous finishes for metals, and particularly aluminum,
none are as versatile as the electrochemical oxidation and
anodizing process. The dielectric aluminum oxide film produced by
anodizing aluminum in boric acid solutions may be less than 1,000 A
thick. In contrast, anodic coatings produced in refrigerated
sulfuric acid solutions may be more than 0.005 inch (127 microns)
thick. There are numerous types of anodizing electrolytes that have
been employed to produce an oxide coating with useful properties.
However, sulfuric acid anodizing is the most common in this
country. Many millions of pounds of aluminum products for
applications requiring attractive appearance, good corrosion
resistance and superior wearing quality are finished by this
method.
In recent years there has been a substantially increased usage of
anodized aluminum in architecture and today the use of anodized
curtain walls, panels, window frames and roofing materials for
commercial, residential and industrial buildings accounts for a
very significant part of the total area of aluminum which is
treated. Since the anodic coatings for these purposes are
frequently exposed to severe conditions and are often not easily
accesible for adequate cleaning, substantially thick coatings must
be applied and frequently it has been found more suitable to
produce architectural coatings under hard anodizing conditions both
in order to apply the films more rapidly and also because corrosion
resistant coatings formed at low temperatures and consequently at
high voltage are somewhat better.
Architectural anodic oxide coatings for external use are usually
between 0.4 and 1.4 mil thick. A thin coating of about 0.1 mil may
not only be ineffective but may even intensify pitting attack. The
coatings are finished in a large variety of colors and surface
textures, blue, gray, gold, black and silver being some of the
colors most popular today for covering walls and building
panels.
However, it has been found that the uniformity of color formation
is not satisfactory, the finish showing gradation of color and
streaking from batch to batch and within a batch. Furthermore, the
density, abrasion resistance and efficiency of deposit are not
totally acceptable. Since the anodizing process is a balance
between the competitive dissolution and oxide formation processes,
an improvement in the efficiency of coating formation would result
in a saving of time, material and energy as well as decreasing the
volume of waste bath to be discarded or treated to make it
environmentally acceptable.
SUMMARY OF THE INVENTION
An improved bath composition for surface finishing on metal
surfaces is provided by the present invention which is not subject
to the disadvantages nor limitations of the previous bath
compositions and provides dramatic improvement in surface
properties of the coating and performance characteristics of the
bath. The coating bath of the invention provides a chemically
converted surface which is more dense and organized and provides
significant increase in efficiency of coating deposit rate. It has
further been discovered that the anodizing baths of the invention
may be subjected to much higher current density without causing
objectionable burning of the film. Efficiency and uniformity of
dissolution are also provided in etching baths containing the
additive of the invention. Colored films are found to be lustrous,
bright, dense, and uniform, to have good abrasion resistance and to
be very smooth. The films provide excellent cooking characteristics
with foods and do not stick to fried or baked foods at cooking
temperatures. The compositions of the invention will find use in
finishing metal architectural panels, trim, window and door frames,
cooking utensils, automotive parts, aircraft parts, marine
hardware, sheets, tubes, rods and the like.
These and many other attendant advantages of the invention will
become apparent as the description proceeds.
The improved chemical surface finishing bath composition in
accordance with the invention comprises an aqueous vehicle
containing an inorganic oxidant-etchant and an effective amount of
the reaction product of a metal halide and a polyhalo-substituted
alkarylamine. The metal surfaces are processed in a manner
conventional in the art, suitably are preliminary cleaning
treatment and surface brightening or roughening, if desired for
special effect. The part is immersed in the bath and is maintained
in the bath until the desired thickness and quality of coating or
etching has been effected. The article is then removed and
subjected to conventional after-treatment such as sealing, waxing
or dyeing and is then ready for service.
The invention will now become better understood by reference to the
following detailed description when considered in conjunction with
the accompanying drawing.
BRIEF DESCRIPTION OF THE DRAWINGS
The FIGURE is a graph demonstrating the improved anodizing rate of
the anodizing bath of the invention compared to a prior art bath
absent the additive of the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
The detailed description which follows relates to the treatment of
aluminum surfaces, one of the most widely treated metals, but,
obviously, the treatment is applicable to other metals, the
surfaces of which are converted to a passivated metal salt layer
more resistant to corrosion than the untreated metal surfaces such
as of titanium, magnesium, copper, iron or alloys thereof such as
stainless steel. The additive of the invention is generally present
in the bath and in an amount from 0.1 to 50, preferably 1 to 20
grams per liter and is formed from a combination of ingredients
which react to form a fluoro, chloro, bromo or iodo substituted
hydrocarbon aminemetal halide complex capable of improving
deposition rate and coating characteristics. While not desiring to
be bound by theory it is believed that the additive of the
invention causes an organization of the layer that forms which
permits the metal oxide or salt molecules to organize in a faster
manner and to form a more organized, denser deposit providing a
harder, smoother, denser, more abrasion and corrosion resistant
deposit having more even color.
The first ingredient utilized in forming the additive material is
an at least trihalogenated compound of fluorine, bromine, iodine or
chlorine, and a metal, particularly Group 1b, 2, 3a, 4b, 5b, 6b and
8 metals such as copper, magnesium, boron, aluminum, titanium,
vanadium, niobium, chromium and tungsten. A preferred material is
boron trifluoride and especially in a stabilized form as a complex
with a lower alkyl ether such as diethyl ether.
The other necessary ingredient is an alkarylamine, particularly a
fluorinated alkarylamine having a relatively high content of
available and active fluorine atoms which is reactive with the
metal halide. Preferred materials are fluoroalkylaryl compounds
selected from those of the formula: ##STR1## where n is an integer
from .[.1.]. .Iadd.0 .Iaddend.to 4, m is an integer from 1-2 and R
is selected from hydrogen, lower alkyl of 1-9 carbon atoms, lower
alkanol of 1-8 carbon atoms and aryl such as phenyl or aralkyl such
as benzyl and Z is .[.hydrogen or.]. --CX.sub.3 where X is fluoro,
chloro, bromo, .Iadd.or .Iaddend.iodo .[.or R.].. A suitable
material is .alpha.,.alpha.,.alpha.-trifluoro-m-toluidine. The
presence of an amino group is believed to relieve stress in the
deposited film in a manner analogous to the action exhibited by
sulfonamides in electrodeposition or anodizing of aluminum.
The metal halide and fluorinated hydrocarbon can be reacted in
bulk, in solution or suspension in a fluid in liquid or gas
phase.
The reaction is preferably carried out in an organic liquid diluent
or solvent, preferably having a boiling point above 100.degree. C.
Higher molecular weight products are formed in the liquid carrier
and a suspension is formed which can readily be applied to the
surface to be treated.
Suitable diluents are polychloro substituted aliphatic compounds
such as trichloroethylene, carbon tetrachloride,
tetrachloroethylene, difluoro-dichloro-ethylene,
fluorotrichloroethylene or other terminally halogenated alkenes of
2-8 carbon atoms. For purposes of reactivity during forming the
coating material and for inertness and temperature resistance of
the material, the compound is preferably substituted with chlorine
on the carbon atoms adjacent the unsaturation, such as
tetrachloroethylene.
The ratio of the ingredients can be varied within wide limits
depending on the hardness and other desired characteristics of the
film and the economics of maximizing yield. Since the diluent, such
as tetrachloroethylene, is readily available at low cost, it can
predominate in the reaction mixture. Satisfactory yields are
obtained by including minor amounts of from 1-20 parts and
preferably about 2-5 parts by volume of the other ingredients.
Though the order of addition is not critical, it is preferable to
first form a mixture of the diluent and fluorinated hydrocarbon
before adding the metal halide.
A specific example follows:
EXAMPLE 1
An additive was prepared from the following ingredients:
______________________________________ Component Amount
______________________________________ Tetrachloroethylene Cl.sub.2
C.dbd.CCl.sub.2 900-960 ml Boron trifluoride etherate 50-20 ml
(C.sub.2 H.sub.5).sub.2 O . BF.sub.3
.alpha.,.alpha.,.alpha.,-trifluoro-m-toluidine 50-20 ml (C.sub.7
H.sub.6 F.sub.3 N) ______________________________________
The toluidine and tetrachloroethylene were combined and a cloudy
suspension was formed. When the metal halide etherate was added,
globules of a fluffy, waxlike, white precipitate was observed in
copious volume after storage at room temperature. A maximum volume
of waxlike solid of over 1/2 the initial volume of the mixture was
obtained after several days. The wax-like solid was separated by
filtration and washed with methanol and water.
The reaction could be accelerated by heating the mixture to a
higher temperature. The waxlike material was heated to 575.degree.
F and no decomposition or melting of the material was observed.
Since the formation of a waxy solid is observed, a
chloro-fluoro-boro substituted hydrocarbon polymer is believed to
be formed.
EXAMPLE 2
Trichloroethylene was substituted for the tetrachloroethylene of
Example 1. A fluffy, waxlike, gelatinous, lightly colored reaction
product was formed.
EXAMPLE 3
Carbon tetrachloride was substituted for the tetrachloroethylene of
Example 1. A product similar to that of Example 2 was formed.
EXAMPLE 4
When the tetrachloroethylene was eliminated, a more vigorous and
exothermic reaction occurred and a more solid reaction product was
recovered.
EXAMPLE 5
An equivalent amount of BBr.sub.3 liquid was substituted for the
BF.sub.3 etherate of Example 1. The yield was almost doubled, the
reaction product was more soluble in organic solvent and the
suspension in the liquid carrier was more uniform and stable.
EXAMPLE 6
An equal amount by weight of BI.sub.3 crystals were substituted for
the BF.sub.3 etherate of Example 1. The reaction product was less
soluble in organic solvent and separated out as individual hard
particles in lower yield. The product was more soluble in
water.
In the known processes of anodizing metals such as aluminum, the
metal body is placed in a bath of suitable electrolyte and
connected as an anode in a direct current electrical circuit which
includes the electrolyte bath. When current is passed through the
bath, an oxide layer is formed on the surface of the aluminum body
that is characterized by being thicker than an oxide that would
form in air. Bath composition, temperature and electrical
parameters are well known to those skilled in the art and are the
subject of industrial and military specifications. The choice of
bath, concentration thereof, time and temperature parameters,
depend on the alloy being treated and the porosity, density and
color of coating desired. The temperature may be staged as in the
Sanford process as described in U.S. Pat. No. 2,977,294 and the
electrolyte may be mixed such as in the Kalcolor process containing
sulphosalicyclic acid mixed with sulfuric acid or sulphate.
Sulfuric-mellitic acid baths are utilized in the Sanford process
permitting the use of higher anodizing conditions, and it is often
possible to produce a desired color without dyeing by the correct
choice of alloy. For instance, a 3 mil coating has an acceptable
black color on aluminum-silicon alloys while copper-rich alloys
produce a bronze film under the same anodizing conditions.
Hard anodizing typically involves cooling the sulfuric acid
electrolyte to slow down the rate of dissolution of the oxide.
Coatings up to 10 mils can be obtained with a loss of metal about 3
grams per square foot providing coatings giving excellent wear
resistance and heat and electrical insulation.
The limiting film thickness is reached when the rate of chemical
dissolution of the film in the electrolyte is equal to the rate of
film growth. The limiting thickness can be increased by lowering
the temperature, acid concentration or voltage, or by increasing
current density. Of the alternatives, both decreasing acid
concentration and increasing current density require an increase in
voltage, thus leading to a local rise in temperature of the anode.
Cooling the solution is the principal cause of the production of
thick coatings, and at higher current densities the coatings that
are formed will be hard.
Commercial hard anodizing processes can utilize direct current or
superimposed A.C. on D.C. and the voltage may be maintained
constant or increased. A well known D.C. process utilizes a 15%
sulfuric acid electrolyte operated at 20 to 25 amps per square foot
and 0.degree. C. To maintain this current density the initial
voltage of 25 to 30 volts is increased to 40 to 60 volts. This
process is particularly suitable for the production of thick
coatings of 5 mils or more. Where thinner films are required it is
possible to work at higher temperatures. Agitation is important in
many of the low temperature processes operated at high currents and
voltages.
The following table provides typical conditions for practicing
anodizing aluminum in accordance with the invention.
Table I ______________________________________ Ingredient Range
______________________________________ H.sub.2 SO.sub.4 (93%) 5-400
g/l Boro-fluoroamine additive 0.5 to 20 g/l Current density 5-200
amps/dm.sup.2 Temperature -20.degree. C to 100.degree. C Time 2-120
minutes ______________________________________
EXAMPLE 7
A 1 liter bath containing 185 grams per liter of 93% H.sub.2
SO.sub.4 was formed containing 1.2 grams per liter of the additive
of Example 1. The bath was contained in a stainless steel tank
which was connected as cathode and a flat 1 inch square specimen of
aluminum 3003-H14 alloy was connected as anode and inserted into
the bath. The bath temperature was adjusted to 0.degree. C and
after 15 minutes at 100 amps/dm.sup.2, a thick, uniform, dense,
hard coating of anodic aluminum oxide was formed on the specimen.
The additive of the invention causes at least a 40% increase in
deposition rate as well as permitting much higher current densities
without deterioration of the film.
EXAMPLE 8
The procedure of Example 7 was repeated on the same alloy specimen
under the same conditions except that the additive was not present
in the bath. As can be seen in the FIGURE, the deposition thickness
for equivalent times was only 60% of that achieved for the bath
composition of Example 7. Furthermore, the coating was not as
organized nor as dense. The color on the specimens treated
according to Example 8 was less uniform than that achieved on the
specimen treated according to Example 7.
The chemical composition of aluminum alloy 3003 H14 is as shown in
the following table:
Table II ______________________________________ Ingredients Weight,
% ______________________________________ Mn 1.0-1.5% Fe 0.7%
maximum Si 0.6% maximum Cu 0.20% maximum Zn 0.10% maximum Al
Remainder ______________________________________
The hardness of the anodic deposits of Example 7 and 8 was compared
by the conventional commercial scratch test which indicated that
the anodic aluminum oxide deposit on the specimen of Example 7 was
significantly harder than the deposit on the specimen of Example
8.
As previously discussed, the additive of the invention also
provides improvement in the coating rate and coating
characteristics of chemical conversion coatings. Again there are
numerous bath compositions and coating techniques well known in the
art.
Typical aluminum oxide baths contain an oxidizing agent and a basic
salt in an amount from 5 to 50 grams per liter and are operated at
20.degree. to 100.degree. C for 1 minute to 2 hours. A typical bath
solution contains sodium carbonate and sodium chromate in a ratio
of approximately 3 to 1. Another similar bath widely used in this
country consists of potassium carbonate and sodium dichromate.
After treatment the coating is sealed in a potassium dichromate
solution. Other chemical oxidization processes are based on sodium
fluosilicate, oxalate or fluozirconate in combination with a sodium
or ammonium nitrate and a nickel or cobalt salt.
Chemical conversion coatings utilized for preparing a surface for
undercoating or painting also proceed by forming a
chromate-phosphate salt on the surface. This treatment makes use of
an acid solution containing chromates, phosphates and fluorides,
optimally containing 20 to 100 grams per liter of phosphate ion, 2
to 6 grams per liter of fluoride ion, and 6 to 20 grams per liter
chromate ion, with the ratio of fluoride to chromate acid lying
between 0.18 and 0.36. Aluminum surfaces are also treated with a
similar chromate conversion coating based on a mixture of chromate
and fluoride ions and there is a chromate-protein process in which
corrosion resistant coatings of the hardness of enamel are produced
which is applicable not only to aluminum but also to steel, zinc
and brass and employs a solution containing chromate acid or
dichromate, formaldehyde and a protein such as gelatine, casein, or
albumin.
Chemical conversion coatings are usually provided to a depth of at
least 0.10 mil to provide a softer microporous, more inert and
chemically stable and corrosion resistant surface than the
untreated surface. Many times conversion coated surfaces exhibit
uniformly pleasing color. Usually such surfaces are not treated to
a depth of over 1 mil. No dimensional growth or change is usually
achieved by this treatment but simply formation of a
chemically-converted, thin, microporous zone extending inward from
the original surface to a penetration depth of about 0.5 mil.
The conversion coating solutions for titanium generally contain a
mixed salt complex formed from Group I or Group II metal salt of a
reactive anion such as phosphate, borate or chromate; a Group I or
Group II metal halide and an acid, typically a hydroallic acid.
Typically bath compositions and conditions for treating titanium
are presented in the following table.
Table III ______________________________________ Bath Composition
Temperature Immersion Bath Grams per liter .degree. F pH Time, min
______________________________________ 1 50 Na.sub.3 PO.sub.4 .
12H.sub.2 O 185 5.1 to 5.2 10 20 KF . 2H.sub.2 O 11.5 HF solution 2
50 Na.sub.3 PO.sub.4 . 12H.sub.2 O 80 1.0 1 to 2 20 KF . 2H.sub.2 O
26 HF solution 3 40 Na.sub.2 B.sub.4 O.sub.7 . 10H.sub.2 O 185 6.3
to 6.6 20 18 KF . 2H.sub.2 O 16 HF solution
______________________________________
EXAMPLE 9
Sufficient deionized water was added in each case to adjust the
volume to 1 liter and then 1.2 grams per liter of the additive of
Example 1 was added to the solution. The HF solution was a
commercial 50.3 weight percent solution. A thicker more uniform
deposit was provided as compared to titanium articles subjected to
the same compositions and conditions absent the additive of the
invention.
The etchant, conversion, and electrolytic anodic compositions of
the invention containing the additive as described herein will
provide greater efficiency, conserve utilization of energy,
eliminate the volume of waste bath products, and provide harder,
denser, more organized and evenly colored films on the surfaces of
metal articles. The composition of the invention will be useful in
whatever applications of aluminum, magnesium, titanium, copper,
iron and other metals requiring abrasion resistance, corrosion
resistance, hardness, lubricity, bright and even color, and other
such attributes.
It is to be realized that only preferred embodiments of the
invention have been described and numerous substitutions,
modifications and moderations are permissable without departing
from the spirit and scope of the invention as defined in the
following claims.
* * * * *