Note: Descriptions are shown in the official language in which they were submitted.
\
~;
1()86ZS3
This invention relates generally to the surface treat-
ment of aluminum and aluminum alloys, and more specifically
to a process for production of sealed anodic oxide films on
such metal for subsequent coating or painting.
For coating or painting articles of aluminum or
aluminum alloy, there has been known and practiced a process
wherein the articles are first anodized to form oxide films
thereon and wherein coatings are applied to these oxide films
after sealing the pores therein as by live steam, by boiling
water, or by boiling water containing typical chemicals such
as nickel acetate and cobalt acetate. The oxide films sub-
jected to such conventional methods of sealing treatment,
however, have the critical defect of cracking or crazing when
coatings applied subsequently thereon are dried at desired
temperatures of 140C or more.
Heretofore this defect has usually been circumvented
by applying to the sealed oxide films coating material which
dries at less than 140C, although the coatings produced by
such material are of generally inferior quality. For the use
of coating material which dries at higher temperatures, it
has been necessary either: (1) to coat unsealed oxide films
electrophoretically as with a resin paint, thereby sealing
the pores in the oxide films by the resin; (2) to coat oxide
films which have been semisealed, that is, sealed only to
such an extent that the films will not develop cracks during
the subsequent high temperature drying of the coatings formed
thereon; or (3) to coat unsealed oxide films with a resin
paint containing water so that the pores in the oxide films
_ 2 -
1086253
may be sealed by hydration as the coatings thereon are dried
,. .
at high temperatures.
It is an object of this invention to provide a novel,
simplified process for production of sealed anodic oxide
films on aluminum and aluminum alloys, such that they can be
coated subsequently without the above noted difficulties of
the prior art.
Another object of the invention is to provide a process
such that the sealed anodic oxide films can be coated with
material which dries at relatively high temperatures, there
being practically no possibility of the films developing
cracks during the drying of the coatings thereon. -
- A further object of the invention is to provide a -
process such that the sealed oxide films can be coated by any
such desired method as electrophoretic, electrostatic or dip
coating, with equally favorable results.
According to the invention, there is provided -
` a process for coating an article of a basis metal composed
of anodized aluminum or an anodized aluminum alloy, which
comprises: sealing the pores in said base metal by immersing
the same in an aqueous solution of a phosphorus compound at
a temperature of at least 80C, the concentration of said
compound in said solution being in the range from 0.005 to -~
j 100 g per liter; applying a coating on the sealed anodized base
metal, said coating requiring a temperature of at least 140C to
develop suitable strength and hardness; and thereafter baking
the resulting coated article at a temperature of at least 140C
until such strength and hardness properties are achieved.
With anodized aluminum or aluminum alloy subjected
to the sealing treatment according to the invention, the oxide
film develops no cracks when a coating produced subsequently
thereon is dried at temperatures exceeding 140C. Furthermore,
- 3 -
, . . .
. ~, . .
1086ZS3
the inventive process overcomes problems such as poor
adhesion of coatings to the sealed oxide films and the
increase in the electrical resistance of the sealed oxide
films with consequent difficulty in, for example, electro-
` phoretic coating.
The above and other objects, features and advantagesof this invention will become more apparent and understandable
from the following detailed description, Examples and claims.
It is understood that aluminum and aluminum alloys to
be processed in accordance with this invention comprise pure
aluminum and the alloys of pure aluminum and at least one of
such elements as silicon, magnesium, copper, nickel, zinc,
chromium, lead, bismuth, iron, titanium, and manganese.
For anodizing aluminum or any of such aluminum alloys,
the basis metal may first be degreased, rinsed and otherwise
suitably pretreated in the conventional manner. The pre-
treated basis metal is then made anodic in the usual acid
electrolytic solution containing sulfuric acid, oxalic acid,
sulfamic acid or the like, and a suitable voltage is impressed
between the anodic basis metal and a cathode such as lead or
aluminum also immersed in the solution as the counter electrode.
Among suitable phosphorus compounds may be included
phosphoric acid, potassium phosphate, sodium dihydrogen
phosphate, sodium ammonium hydrogen phosphate, diammonium
hydrogen phosphate, disodium hydrogen phosphate, tricalcium
phosphate, potassium dihydrogen phosphate, phosphotungstic
acid, sodium phosphotungstate, phosphomolybdic acid, sodium
phosphomolybdate, phosphorous acid, sodium phosphite, potassium
phosphite, disodium hydrogen phosphite, diammonium hydrogen
- 30 phosphite, triethyl phosphate, and aniline phosphate. Phosphoric
acid includes ortho-, pyro-,and meta-phosphoric acids.
-- 4 --
~, '
.. . ' . . ~ -, . , - ' '':
: :. . , . . . , . : .
1086253
The concentration of the selected phosphorus compound
in the aqueous solution is in the range of fromabout 0.005 to 100
grams per liter, and preferably from about 0.01 to 30 grams
per liter. It has been confirmed by experiment that anodic
oxide films when sealed by the aqueous solution containing any
selected phosphorus compound in the specified range of con-
centration have better corrosion resistance and less porosity
than when sealed, for example, by boiling water containing
commerically available chemicals such as nickel acetate and
cobalt acetate or by boiling water.
For sealing treatment, anodized aluminum or aluminum
alloy is immersed in the above described aqueous solution
from about 10 to 60 minutes. Thereafter, the anodized basis
metal may be rinsed and dried where necessary, and then a
desired coating is applied to the sealed oxide film thereon.
Coating material for use should be of the class that
must be baked at temperatures at least about 140C to
.'~ .
- ~ ~ - ~: - :
. , ~
.. ,, -
~0~6ZS3
.
develop desired final properties of strength and hardness.
Any known or suitable coating method can be employed, such
as electrophoretic coating, electrostatic coating, or dip
coating. The coating produced on the sealed oxide film is
S then dried by baking at about 140C or more.
The sealing of anodic oxide films by use of a heated
aqueous solution of a phosphorus compound in accordance with
this invention is effective not simply to improve their cor-
rosion resistance. The inventive process totally eliminates
the conventional deficiency of fluctuations in the quality
and appearance of coatings produced electrophoretically on
unsealed or semisealed anodic oxide films, such fluctuations
having been caused heretofore by residual sulfuric acid or
like impurity material within the pores of the oxide films.
Another advantage of the inventive process is that it
permits the use of coating material which dries at relatively
high temperatures. Japanese Patent Publication No. 47-51092
discloses a process comprising initial sealing treatment of
anodic oxide films with a metallic salt and, after electro-
phoretically coating the films with a thermosetting resin,
secondary sealing treatment wherein the pores in the films
are further sealed as the coatings thereon are dried at high
temperatures within a drying furnace. Contrastively, in ac-
cordance with the inventive process, a single step of sealing
treatment suffices to give desired effects, and further it
permits the use of the electrophoretic~ electrostatic, dipping
or any other suitable method for coating the sealed oxide films.
If desired, oxide films which have been subjected to
-- 6 --
:
:
: : ~' ~ ' ' ~ . . `
:
.
- :
.~- .
.
10862S3
sealing treatment with a heated aqueous solution of a phos-
phorus compound according to the invention may be further
treated with live steam or like conventional sealing means.
In this manner the merits of the secondary sealing treatment
will be added to the oxide films without impairment of the
merits imparted thereto by the initial sealing treatment with
the heated aqueous solution of a phosphorus compound.
The invention is hereinafter described more specifically
in terms of se-veral Inventive Examples, which, however, are
meant purely to illustrate or explain and not to impose limita-
tions upon the invention. Also given hereinbelow are some
Comparative Examples which are intended to make clear the
advantages of the inventive process.
Inventive Examples 1 - 10
Specimens each consisting of an ~uminum extrusion
sized 150 millimeters by 70 by 1.3 were degreased, etched and
desmutted in the usual manner. Each specimen which had been
pretreated as above was made anodic in an aqueous solution of
17.5 W/V % sulfuric acid, which had a temperature of 20C, and
a direct current voltage of 16 volts was impressed for 30
minutes between the anodic specimen and an aluminum cathode
also immersed in the bath as the counter electrode. The
current density was 1.3 amperes per square decimeter. An
oxide film with a thickness of about 12 microns was thus
formed on each specimen, which was then rinsed.
For sealing treatment, the anodized specimens were
immersed in respective heated solutions which had been
prepared by dissolving in pure water the phosphorus compounds
-' : ': '
~8fi2S3
listed in Table 1 below. The specimens were then rinsed and
dried at room temperature. The spcific conditions of the
sealing treatment are given also in Table 1. The specimens
of only Inventive Examples 8 and 9 were subjected to additional
sealing treatment by live steam, under pressure of five kilo-
grams per square centimeter, for 30 minutes.
Table 2 below gives the test results of the sealed
oxide films on the various specimens. The tests were conducted
as follows:
Alkaline dropping corrosion resistance test
This test was effected in accordance with the Japanese
Industrial Standard (JIS~ H 8681 specification. Sodium
hydroxide was dissolved in desalted water, with a
concentration of exactly 10 W/V percent. This reagent
was dropped on the cleaned surface of each specimen at
constant intervals of five seconds, with each drop
weighing about 16 milligrams, until the basis metal
was exposed. Both specimen, reagent and ambience were
held at a temperature of 35C. Table 2 gives the
length of time in seconds until the basis metal of
each specimen was exposed.
CASS test -
This test was also effected in accordance with the -
JIS H 8681 specification. For preparation of a re-
agent, sodium chloride was dissolved in desalted water,
with a concentration of four W/V percent, and cupric
chloride was further dissolved in the solution, with a
concentration of 0.26 gram per liter. Acetic acid was
~. . : ' : .: ~
- . ~
: : :
.
. . . ~ :
.
~086253
then added to the solution to reduce its pH to three.
By use of compressed air under pressure of one kilo~
gram per square centimeter, the thus prepared reagent
was sprayed for eight hours onto each specimen at a
rate of from one to two milliliters per 80 square
centimeters per hour. Both specimen and reagent were -
held at a temperature of 50C. Table 2 gives the con-
sequent degrees of corrosion of the various specimens
in "rating numbers" as provided for by JIS H 8681.
Kape~s test
To an aqueous solution containing 10 grams per liter
of sodium sulfite was added glacial acetic acid to
regulate the pH of the solution to 3.75, and to this
solution was further added 5N sulfuric acid to reduce -
its pH to 2.5. The solution was then heated to a
temperature of 92C. The specimens were immersed for -
30 minutes in this heated solution, and the consequent
changes in their surface conditions were observed.
Coatings were then applied to the sealed oxide films
on the specimens of each Example by the electrophoretic, dip
and electrostatic coating methods, in accordance with the
following procedures: -
Electrophoretic coating
Each specimen was made anodic in a 12 weight percent
aqueous solution of electrophoretic coating material
(thermosetting acrylic resin paint) having a tempera-
ture of 22C, and a direct current voltage ranging `from 140 to 180 volts was applied for two minutes
.. . ~ .
- . - :
1086253
between the anodic specimen and a stainless steel
cathode immersed in the solution as the counter
electrode. The thus coated specimen was rinsed and
then dried at a temperature of 180C for 40 minutes.
A coating with a thickness of about seven microns was
thus formed on each specimen.
Dip coating
Each specimen was immersed in a 26 weight percent
aqueous solution of dip coating material (thermosetting
acrylic resin paint) having a temperature of 40C.
The specimen was withdrawn from the solution at a
speed of about one meter per minute. After having
been allowed to stand for 10 minutes at an ambient
temperature of 35C, the coated specimen was dried at
a temperature of 180C for 40 minutes. A coating with
a thickness of about seven microns was thus formed on
each specimen.
Electrostatic coating -
A thermosetting acrylic resin paint was thinned with
a thinner at a ratio of one to one. The tinned paint
was air sprayed at a pressure of four kilograms per -
square centimeter onto each specimen. A voltage of
60,000 to 90,000 volts was applied between the air
spray nozzle and the specimen. The thus coated speci-
men was allowed to stand for 10 minutes and was then
dried at a temperature of 180C for 20 minutes. A
coating with a thickness of about seven microns was
thus formed on each specimen.
_ 10 --
'
,
lOl~fi2S3
Table 2 also shows the presence or absence of cracks
in the thus coated oxide films on the various specimens. Also
given in Table 2 are the test results as to the adhesiveness
of the coatings to the basis metal. The adhesiveness of the
coatings was determined in accordance with the Dupont impact
test (1/4~R x 500g x 50 cm) and the JIS H 4706 adhesion test.
In the latter test, crisscross c~ts were made on the coating
of each specimen by means of a razor to form 100 squares each
measuring one millimeter by one. An adhesive cellophane tape
with a width of 12 millimeters was stuck on the crisscrossed
surface portion of the specimen and was immediately raised
off the surface to see if the squares would peel off.
Comparative Example 1
The procedure of Inventive Example 1 was repeated ex-
cept that pure water at a temperature of 95C was used instead
of the aqueous solution of phosphoric acid for sealing the
pores in the anodic oxide films. The results are as given in
Tables 1 and 2.
Comparative Example 2
The procedure of Inventive Example 1 was repeated ex-
cept that the sealing treatment was effected for 30 minutes
by use of live steam under pressure of five kilograms per
square centimeter~ instead of the aqueous solution of phos-
phoric acid. The results are as given in Tables 1 and 2.
Comparative Example 3
The procedure of Inventive Example 1 was repeated ex-
cept that an aqueous solution containing 5.6 grams per liter
of nickel acetate and 1 gram per liter of cobalt acetate
.
-- 11 _
: . . ..
- , : ,
.
-: ' : : : .
~086Z53
and 8.4 grams per liter of boric acid ~as used instead of the
aqueous solution o$ phosphoric acid. The results are as given
in Tables 1 and 2.
' ' .
:-
- 12 -
108tiZS,3
~ 0 X X X
. . . . . . . ~ ~ . . ,~
~o ~, . . . . . . . ~ . ~ . . . ~3 .
,~' ,a . . . . . . . ,~ ,-, ,~ ,~ . . ,.~,,
~ 1~ '2D ~ ~D d ~D ~!
0 i~ . . . . .. . y ,~ . . ,~ .
G~ ,~ . O O O -
,n ~ . . . .. . . ~ , .
ii
.~
~ ~ `1 ~
o
.
. .
~ Ir> ~ O ~ o U) itl--) i1~ i~U) --i
'` : ~ i0
. ,~
~ _
i
~ ~ ~ .~
~ I_~ i
~ ~ : :
1~ ~_ ~ i~
~o o o o
. . ~
i~o
~ _ ... . I
,$ i'R 1~
o ,q ~ ~ ,5 * ,-a
' O O 1) ~. i'R
,~ ii ,-' ~ ,~, ~ iD --I ,-a
a o ,~ o ~ ¢
~D .~ ,a ,~ *
¢ iQ ~ a i'R ~ 1~
~0 ~ 0 ~0 ~
i~ )
_
O l~ iX ~ ~ ~ O ~ O ,~
-I ~ l i~
~ ~ V
. X D ~ = = = = = - ~ '',
., ,~ X o X
.. .__ U ~ ___
. - 13 -
.
:
-
108fiZ53
. ..... ._ ._ .
~ ~ C ~ ~ . . .
o a~
~-1 ~
a~
o o o o o o o V o o . . .
~ X X X X X X X X X X
¢ ~ . . .
` , .
. I,olb~
~-,~ o o o o o o o o o o
o ~ ~ z z z z z ~ z z z z c~
o ~ ~ ~
o .,
_
~Q ~
~ ~rl O O O O O O O O O O ~ q
- ~o ~ ., Z Z Z Z Z Z Z Z :Z Z ~ ~ ~
o
_ _ .... _ .. _ _
OrlbD
~ O rl O O O O O O O O O O
~o ~ ~ Z Z Z Z Z z Z z ~ z a~
~1 ~
~o
_ . . . __
$ $ $ $ $ $ ~ ~ $ $ $
o o o o o o o o o o o
a) 5
_
G.~ ~ ~q ~ ~ ~ ~ q~ ~ ~ ~ ~ q~ ~ ~ q~
Q$ o ~ o
~4 ~ ~ ~ ~ ~ ~ ~ P. ~ h ~ P,
" ~ ~ 'C ~?
_ _ . .
U2 ~_ ~ oo oo o~ oo ~ ~~o .'
U~ ~ ~i . . . . . . . .
~ $~ ~ o ~o ~o ~ o~o o~
_ . ._
_
~ ~00
O ~O O O U~ O U) O O O O O O
I~ 1:` 1~ 1` ~ r) t` 00 ~ `O t` 00 t`
~ ~0 ~ ~1 ~1
¢~
. .. _ .
~1 ~ o ~
~
e c t~
x ~ x ~ = = = ~ ~ e ==
H~ Oel:~3
, __ _ ____ _ , _ ~) ,_
-- 14 _
