Note: Descriptions are shown in the official language in which they were submitted.
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Descri tp ion
COMPOSITION AND PROCESS FOR TREATING METAL SURFACES
FIELD OF THE INVENTION
This invention relates to a novel aqueous liquid composition, which is usually
hereinafter called a "bath" for brevity, without any implication thereby that
it must be used
by immersion only, and to a process for treating a metal surface. The
composition and
process can provide the surfaces of various metals, especially aluminum,
aluminum al-
loys, magnesium, magnesium alloys, and galvanized steel sheet, with an
excellent corro-
sion resistance and excellent paint adherence.
The baths used to treat aluminum and aluminum alloy surfaces can be broadly
classified into chromate-type baths and non-chromate-type baths. Chromic acid
chro-
mate conversion baths and phosphoric acid chromate conversion baths are
typical ex-
amples of the chromate-type treatment baths.
Chromic acid chromate conversion baths first reached practical application in
about 1950 and even now are widely used for the surface treatment of
automotive heat
exchangers, aluminum wheels, building materials, and aerospace materials. The
main
~s components in chromic acid chromate conversion baths are chromic acid and a
fluoride
reaction accelerator. This type of bath produces a conversion coating
containing moder-
ate amounts of hexavalent chromium on the metal surface.
Phosphoric acid chromate conversion baths originated with the invention dis-
closed in United States Patent No. 2,438,877. The main components in
phosphoric acid
Zo chromate conversion baths are chromic acid, phosphoric acid, and
hydrofluoric acid. A
conversion coating whose main component is hydrated chromium phosphate is
formed
by this type of bath on the metal surface. Since the resulting conversion
coating does
not contain hexavalent chromium, this type of bath is in wide use at the
present time as
an underpaint treatment for the body stock and lid stock of beverage cans.
is While the conversion coatings generated by these chromate-type surface
treat-
ment baths exhibit an excellent corrosion resistance and an excellent
adherence to paint
films, these treatment baths also contain toxic hexavalent chromium, and the
associated
environmental problems have made it desirable to use treatment baths that are
com-
pletely free of hexavalent chromium.
3o The treatment bath disclosed in Japanese Laid Open (Kokai or Unexamined)
Pat-
ent Application Number Sho 52-131937 (131,937/1977) is an invention typical of
the
chromium-free non-chromate-type surface treatment baths. This surface
treatment bath
is an acidic (pH = approximately 1.5 to 4.0) aqueous coating solution that
contains phos-
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phate, fluoride, and zirconium or titanium or a mixture thereof. The treatment
of metal
surfaces with this surface treatment bath results in the formation on the
metal surface
of a conversion coating whose main component is an oxide of zirconium or
titanium.
This non-chromate-type surface treatment bath offers the advantage of not
containing
s hexavalent chromium and for this reason is widely used at present for
treating aluminum
drawn-and-ironed, hereinafter usually abbreviated as "DI", can surfaces.
Unfortunately,
the coating produced by this non-chromate-type surface treatment bath is less
corrosion
resistant than chromate coatings.
The treatment method disclosed in Japanese Laid Open (Kokai or Unexamined)
Patent Application Number Sho 57-41376 (41,376/1982) comprises treating the
surface
of aluminum, magnesium, or an alloy thereof with an aqueous solution
containing at least
one selection from titanium salts and zirconium salts, at least one selection
from imida-
zole derivatives, and an oxidizer selected from nitric acid, hydrogen
peroxide, and potas-
sium permanganate. While the corrosion resistance of the coatings produced by
this
a treatment bath would have been considered acceptable 15 years ago, this
level of cor-
rosion resistance is not unequivocally satisfactory at the present time.
Japanese Laid Open (Kokai or Unexamined) Patent Application Number Sho 56-
136978 (136,978/1981 ) teaches a conversion bath that characteristically
comprises an
aqueous solution containing a vanadium compound and at least one compound
selected
from the group consisting of titanium salts, zirconium salts, and zinc salts.
However, the
conversion coating formed by this treatment bath cannot be expected to have a
corrosion
resistance better than or even as good as that of a chromate film in the case
of challenge
by long-term anticorrosion testing.
Thus, as described above, the use of the aforementioned prior-art non-chromate
zs type surface treatment baths remains associated with problems with the
corrosion resist
ance of the produced conversion coatings. It is for this reason that at
present non
chromate-type surface treatment baths are little used on surface treatment
lines where
a particularly good corrosion resistance is required, for example, for
aluminum alloy heat
exchangers and aluminiferous metal coil and sheet stock.
3o In summary, then, there has yet to be established a bath for treating
aluminum
and aluminum alloy surfaces that does not contain hexavalent chromium, that
has an
excellent effluent treatability, and that has the ability to form highly
corrosion-resistant,
highly. paint-adherent conversion coatings.
For treating magnesium surfaces and magnesium alloy surfaces, chromate
3s treatments as typified by JIS (Japanese Industrial Standard) H-8651 and MIL
M-3171 are
in use for treating magnesium and magnesium alloy surfaces. The conversion
coatings
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generated by these chromate-type surface treatment baths exhibit an excellent
corrosion
resistance and an excellent adherence to paint films, but these treatment
baths also con-
tain highly toxic hexavalent chromium. The associated environmental problems
have
made it desirable to use treatment baths that are entirely free of hexavalent
chromium.
s The process disclosed in Japanese Patent Publication Number Hei 3-6994
(6,994/1991 ) is an invention typical of the chromium-free non-chromate-type
surface
treatment baths for magnesium and its alloys. This treatment process comprises
a
phosphate treatment followed by a silicate treatment and then execution of a
silicone
treatment after the silicate treatment. The phosphate treatment coating by
itself provides
a low level of corrosion resistance and paint adherence when used as an
underpaint
treatment for magnesium and magnesium alloy surfaces. This treatment method
also
requires a multistage treatment process, uses high treatment temperatures, and
requires
long treatment times.
The known phosphate-based surface treatment methods for magnesium and its
~s alloys include methods that employ treatment baths based on zinc phosphate,
iron
phosphate, calcium phosphate, or zirconium phosphate. However, these methods
are
not believed to have consistently provided a corrosion resistance that is
satisfactory at
a practical level.
A manganese phosphate treatment is disclosed in category 7 of JIS H-8651.
zo This treatment bath is not acceptable from a practical standpoint because
it contains
chromium, requires high treatment temperatures of 80 °C to 90
°C, and requires long
treatment times of 30 to 60 minutes.
Another example of the non-chromate-type technology is found in Japanese Laid
Open (Kokai or Unexamined) Patent Application Number Hei 9-228062
(228,062/1997),
zs which teaches a surface treatment process that uses an aqueous solution
that contains
at least one organometal compound selected from metal alkoxides, metal
acetylaceton-
ates, and metal carboxylates and at least one film-formation stabilizer or
film-formation
auxiliary selected from acids, bases, their salts, and organic compounds
containing the
hydroxyl group, carboxyl group, or amino group. This aqueous solution is
applied to
3o magnesium stock at from 0 to 50 °C. Again, however, the conversion
coating formed by
this treatment bath cannot be expected to have a corrosion resistance better
than or
even as good as that of a chromate film in the case of challenge by long-term
anticorrosion testing.
Thus, as described above, the use of the aforementioned prior-art non-chromate-
3s type surface treatment baths for magnesium and its alloys remains
associated with
problems with the corrosion resistance of the produced conversion coatings and
with
3
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requiring treatment conditions unsuitable from a practical standpoint, i.e.,
high treatment
temperatures, long treatment times, and high bath concentrations. It is for
these reasons
that at present non-chromate-type surface treatment baths are little used on
surface
treatment lines where a particularly good corrosion resistance and paint
adherence are
s required, for example, for magnesium alloy automotive materials, aerospace
materials,
materials for electronic devices and instruments, and materials for
communication
devices and instruments.
In summary, then, there has yet to be established a bath for treating
magnesium
and magnesium alloy surfaces that does not contain hexavalent chromium, that
has ex-
cellent process characteristics, and that has the ability to form highly
corrosion-resistant,
highly paint-adherent conversion coatings.
Chromate treatments and zinc phosphate treatments are the treatment processes
generally applied to galvanized materials. The chromate treatments provide an
excellent
coating performance, but the corresponding treatment baths contain toxic
chromium and
~s hence raise issues with regard to the working environment and effluent
discharge. The
zinc phosphate treatments in some cases are unable to provide an acceptable
corrosion
resistance.
The non-chromate-type technologies for galvanized materials can be exemplified
by the processes disclosed in the following patent documents: Japanese Laid
Open (Ko-
kai or Unexamined) Patent Application Number Hei 1-104783 (104,783/1989)
discloses
a process for producing surface-treated steel sheet. In this process, steel
sheet plated
with zinc, aluminum, or a zinc-aluminum alloy is coated with an alcohol
solution contain-
ing at least one selection from the alkoxides and acetylacetonates of Si, Ti,
Zr, AI, W, Ce,
Sn, and Y. An oxide of the metal present in the solution is then formed on the
surface
is of the steel sheet by heating to 200 to 500 °C after application of
the bath. This prepara-
tive method suffers from issues with the working environment and energy costs,
because
it must use a flammable alcohol and requires fairly high temperatures for
coating
formation.
Thus, just as in the case of aluminum materials and magnesium materials, there
has yet to be established a bath for treating the surfaces of galvanized
materials that
does not contain hexavalent chromium, that has excellent process
characteristics, and
that has the ability to form highly corrosion-resistant, highly paint-adherent
conversion
coatings.
The present invention is directed to solving the problems described above for
the
ss prior art. In more specific terms, a major object of the present invention
is to provide a
non-polluting composition and process for treating surfaces of at least one of
aluminum
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WO 00/24948 PCTNS99/23982
and its alloys, magnesium and its alloys, and steel coated with zinc and its
alloys that can
impart thereto an excellent corrosion resistance and excellent paint
adherence.
BRIEF SUMMARY OF THE INVENTION
It has been found that highly corrosion-resistant, highly paint-adherent
conversion
s coatings can be formed on metal surfaces by the use of a special surface
treatment
composition that contains in suitable proportions at least one metal
acetylacetonate
selected from the group consisting of AI(CSH702)3, V(C5H,O2)3, VO(C5H,0z)2,
Zn(C5H,02)2, and Zr(C5H702)4, and at least one compound selected from water-
soluble
inorganic titanium compounds and water-soluble inorganic zirconium compounds.
io DETAILED DESCRIPTION OF THE INVENTION AND PREFERRED EMBODIMENTS
A composition according to the present invention for treating metal surfaces
comprises, preferably consists essentially of, or more preferably consists of,
water and
the following components:
(A) a component of at least one metal acetylacetonate selected from the group
con-
s sisting of AI(C5H,02)3, V(CSH,02)3, VO(CSH702)2, Zn(C5H702)2, and
Zr(C5H,02)4;
and
(B) a component of at least one compound selected from water-soluble inorganic
ti
tanium compounds and water-soluble inorganic zirconium compounds,
components (A) and (B) being present at a weight ratio of (A) to (B) that is
from 1 : 5,000
zo to 5,000 : 1.
A bath according to the present invention for treating metal surfaces
preferably,
independently for each preference:
- hasapHfrom2.Oto7.0;
- contains from 0.01 to 50 grams of component (A) as described above per liter
of
zs bath, this unit of concentration being freely applied hereinafter to any
constituent
of the bath and being usually abbreviated as "g/I"; and
- contains from 0.01 to 50 g/l of component (B) as described above.
A process according to the present invention for treating metal surfaces
preferably forms on said metal surface an organic-inorganic composite
conversion
3o coating at a coating weight of 5 to 2,000 milligrams of coating per square
meter of the
surface coated, this unit of coating weight being hereinafter usually
abbreviated as
"mg/m2", by bringing the above-described bath for treating metal surfaces into
contact
with aluminum or an alloy thereof, magnesium or an alloy thereof, or zinc or
an alloy
thereof.
3s An important feature of the present invention is the formation of an
organic-
inorganic composite coating. It is believed that the corrosion resistance of
the resulting
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conversion coating in particular is improved through the formation of this
organic-
inorganic composite coating.
The water-soluble inorganic titanium compound and/or water-soluble inorganic
zirconium compound, which is an essential component in the surface treatment
composi-
s tion of the present invention, can be one or more selections, for example,
from the sul-
fates, oxysulfates, nitrates, phosphates, chlorides, ammonium salts, and
fluorides of ti-
tanium and zirconium. As long as this component is a water-soluble inorganic
com-
pound, its specific type is not critical. However, at least for economy, at
least one of
fluorotitanic and fluorozirconic acids and the salts of both of these acids
are preferred.
The water-soluble inorganic titanium and/or zirconium compounds) are believed
to pre-
cipitate on the surface of the metal workpiece as, for example, the oxide,
phosphate, or
fluoride of Ti or Zr and thus to form a framework or skeletal element of the
organic-inor-
ganic composite coating that is produced with the simultaneously precipitating
metal
acetylacetonate. Moreover, the presence of the Ti and/or Zr also improves the
barrier
~s performance (interception capability) of the coating with respect to
corrosive environ-
ments and as a result makes possible the formation of a coating that has a
corrosion re-
sistance and paint adherence superior to the use of only the metal
acetylacetonate.
The metal acetylacetonate : water-soluble inorganic compound concentration
ratio preferably is at least, with increasing preference in the order given,
1.00:100,
20 1.00:50, 1.00:10, 1.00:7.0, 1.00:5.0, 1.00:3.0, 1.00:2.0, or 1.00:1.40 and
independently
preferably is not more than, with increasing preference in the order given,
400:1.00,
100:1.00, 10:1.00, 7.0:1.00, 5.0:1.00, or 2.5:1.00. The organic-inorganic
composite
coating formed when this weight ratio is below 1:5000 will have a poor
corrosion
resistance, while production of the organic-inorganic composite coating itself
becomes
zs difficult at above 5000:1.
A bath according to the present invention for treating metal surfaces
essentially
employs water and the hereinabove described surface treatment composition.
This bath
contains the metal acetylacetonate preferably at from 0.01 to 50 g/I and more
preferably
at from 0.1, or still more preferably, 1.0, to 20 g/I. While a conversion
coating will be
3o formed at a metal acetylacetonate content below 0.01 g/l, such a coating
will usually
have a poor corrosion resistance and paint adherence. Good quality conversion
coatings are still formed at above 50 g/I, but since no additional increment
in
performance is obtained above 50 g/I, such concentrations are uneconomical due
to the
additional cost of the bath.
ss The content of water-soluble inorganic titanium compounds) and/or water-
soluble inorganic zirconium compounds) is preferably from 0.01 to 50 g/I and
more
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preferably from 0.05, or still more preferably 0.5, to 10 g/I. While a
conversion coating
will be formed at a content below 0.01 g/l, such a coating will usually have a
poor
corrosion resistance. Good quality conversion coatings are still formed at
above 50 g/l,
but since no additional improvement in performance is obtained above 50 g/I,
such
s concentrations are uneconomical due to the additional cost of the bath.
The pH of a surface treatment bath according to the present invention must be
within the range from 2.0 to 7.0 and preferably is within the range from 3.0
to 6Ø A pH
below 2.0 hinders precipitation of the metal acetylacetonate on the metal
surface and
can cause irregularities or unevenness in appearance due to excessive etching-
of the
metal surface. Formation of a highly corrosion-resistant conversion coating is
strongly
impaired at a pH above 7.0, and a pH above 7.0 can also cause problems with
bath
stability due to a pronounced tendency for the metal ions present in the bath
to form a
precipitate at such pH values. As necessary, the pH of the surface treatment
bath of the
present invention can be adjusted into the desired range through the use of an
acid such
~s as nitric acid, sulfuric acid, phosphoric acid, hydrofluoric acid, or
fluorosilicic acid, or a
base such as sodium hydroxide, sodium carbonate, potassium hydroxide, or
ammonium
hydroxide.
The stability of the treatment bath can be strongly impaired during execution
of
the surface treatment of the present invention by elution into the bath of
metal ions, e.g.,
zo aluminum, magnesium, or zinc ions, from the metal workpiece. In such cases,
an
organic acid or alkali metal salt thereof may be added to the bath as a
sequestering
agent in order to chelate the metal ions. Organic acids used for this purpose
can be
exemplified by gluconic acid, heptogluconic acid, oxalic acid, tartaric acid,
organophosphonic acids, and ethylenediaminetetraacetic acid.
zs An oxidizing agent can also be used in order to accelerate formation of the
conversion coating of the present invention. This oxidizing agent can be
exemplified by
hydrogen peroxide, tungstic acid and its salts, molybdic acid and its salts,
permanganic
acid and its salts, and water-soluble organoperoxides such as tert-butyl
hydroperoxide
((CH3)3C-O-OH).
3o The mass per unit area, usually called "coating weight", of the organic-
inorganic
composite conversion coating formed by the hereinabove described process is
preferably from 5 to 2,000 mg/m2 and more preferably is from 50, or still more
preferably
140, to 500 mg/m2. The corrosion resistance and paint adherence may be
inadequate
at a coating weight below 5 mg/m2. While an excellent corrosion resistance is
obtained
3s at coating weights above 2,000 mg/m2, no additional increment in
performance is
obtained above 2,000 mg/m2 and such coating weights are therefore uneconomical
due
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to the additional cost. Coating weights above 2,000 mg/m2 are also undesirable
because
they can cause a conspicuous unevenness in coating appearance and tend to
impair the
paint adherence.
In regards to the metal components (AI, V, Zn, Zr, Ti) that may constitute the
s conversion coating, their chemical characteristics in the coating itself,
for example, their
bonding status, oxidation state, extent of polymerization or increase in
molecular weight,
and the like, are not critical.
Highly corrosion-resistant, highly paint-adherent conversion coatings can be
formed by bringing the surface treatment bath of the invention into contact
with aluminum
or an alloy thereof, magnesium or an alloy thereof, or zinc or an alloy
thereof. This pro-
cess for treating the surface of various types of metals will be explained in
greater detail
in the following.
The surface treatment bath of the invention is used in a preferred embodiment
as part of the following process operations:
~s (1 ) Surface cleaning/degreasing (this can be acidic, neutral, alkaline, or
solvent
cleaning/degreasing)
(2) Water rinse
(3) Surface treatment using the surface treatment bath of the present
invention
(4) Water rinse
zo (5) Deionized water rinse
(6) Drying.
The surface treatment bath of the present invention is preferably brought into
contact with the metal surface for 1 to 600 seconds at 10, or more preferably
35, to 80
°C. The reactivity between the treatment bath and metal surface usually
will be
zs inadequate at contact temperatures below 10 °C, and inadequate
reactivity will prevent
the formation of good quality conversion coatings. A conversion coating is
still formed
at contact temperatures above 80 °C, but the correspondingly increased
energy costs
create undesirable economics for such temperatures. The extent of reaction
will usually
be inadequate at a treatment time below 1 second, preventing the formation of
a highly
so corrosion-resistant conversion coating. At the other end of this range, no
additional
improvements are seen in the corrosion resistance and paint adherence of the
conversion coating at times in excess of 600 seconds. Contact with the surface
treatment bath of the invention can be effected by any means that achieves the
required
contact, with dipping or spraying being most commonly used.
3s A surface treatment composition bath according to the invention can be
advan-
tageously applied to pure aluminum and aluminum alloys that contain at least
50 % by
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WO 00/24948 PCT/US99/23982
weight of aluminum. The applicable aluminum alloys encompass both
multicomponent
alloys, e.g., AI-Cu, AI-Mn, AI-Si, AI-Mg, AI-Mg-Si, and AI-Zn-Mg, and metals
on which AI
plating or AI alloy plating has been executed, for example, AI-plated steel
sheet.
The surface treatment composition and bath according to the invention can also
s be advantageously applied to pure magnesium and magnesium alloys that
contain at
least 50 % by weight of magnesium. Applicable magnesium alloys encompass multi-
component alloys such as Mg-AI-Zn, Mg-Zn, and Mg-AI-Zn-Mn, and the magnesium.
or
alloys can be plated on other metals.
Zinc and zinc alloys to which the invention can be advantageously applied
include
in particular metals on which Zn plating has been executed, including hot-dip
zinc-plated
steel sheet, galvannealed hot-dip zinc-plated steel sheet, AI2n alloy-plated
steel sheet
(GaIfanT"" and GalvalumeT"~), electrogalvanized steel sheet, and alloy
electrogalvanized
steel sheet.
Such factors as the shape and dimensions of the metallic substrate to which
the
~s invention is applied are not critical, and, for example, the invention
encompasses the
treatment of sheet stock and various types of moldings. The surface of the
workpiece
may be in any condition as long as a metal as described above is present at
least at a
portion of the surface. For example, the surface can be cold rolled or plated
as such, or
can have been subjected to a treatment such as shot blasting, roughening with
acid or
alkali, or activation.
The effects of the composition, bath, and process of the invention are
illustrated
more specifically below through working and comparative examples.
EXAMPLES 1 TO 5 AND COMPARATIVE EXAMPLES 1 TO 4
The following sample substrate materials were used in these examples:
is AL-Mn alloy sheets according to Japanese Industrial Standard {uJIS") 3004,
with dimen-
sions of 150 millimeters (hereinafter usually abbreviated as "mm") x 70 mm x
0.2
mm thick;
Die-cast sheets with dimensions of 150 mm x 100 mm x 1 mm thick of AZ91 D
rriagnes-
ium alloy as specified by JIS H2222; and
3o Galvannealed hot-dip zinc-plated steel sheets with dimensions of 150 mm x
70 mm x
0.8 mm thick.
PROCESS CONDITIONS
The surface-treated samples were prepared by treatment according to the
following operations in the sequence (1 ) ~ (2) ~ (3) ~ (4) ~ (5) - (6).
3s (1 ) Degreasing (43 °C, 2 minutes, dipping), using an aqueous
solution of 2 % FINE-
CLEANER~ L4460A and 1.2 % FINECLEANER~ L4460B (both commercial products
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of Nihon Parkerizing Co., Ltd.).
(2) Tap water rinse (ambient temperature, 30 seconds, spray).
(3) Surface treatment (dipping) as detailed in the tables below.
(4) Tap water rinse (ambient temperature, 30 seconds, spray).
s (5) Deionized water rinse (ambient temperature, 30 seconds, spray).
(6) Drying (80 °C for 3 minutes in a forced convection oven).
("Ambient temperature" means temperature as normally maintained in buildings
for
human comfort, i.e., about 18 - 23 °C.)
The metal acetylacetonates used are listed below in Table 1, the water-soluble
titanium compounds used are listed below in Table 2, the water-soluble
zirconium com-
pounds used are listed below in Table 3, and the reagents used to adjust the
pH of the
surface treatment baths are listed below in Table 4, in each instance together
with the
identifying symbols used for them in later tables.
Table 1
Acetylacetonate Source Name Identifying
and Chemical Formula
Symbol
Aluminum acet lacetonate A1 C H O ) a
Vanadium acet lacetonate V(C H O ) b
Vanad 1 acet lacetonate VO(C H O ) c
Zinc acet lacetonate Zn(C H O ), d
Zirconium acet lacetonate Zr(C H O ) a
Table 2
Titanium Source Name and Chemical Formula Identifying
Symbol
40 % Solution in water of fluorotitanic acid A
H TiF
20 % Solution in water of titanium sulfate B
Ti(SO
Table 3
Zirconium Source Name and Chemical Formula Identifying
Symbol
20 % Solution in water of fluorozirconic acida
H ZrF
Ammonium fluorozirconate (NH ),ZrF
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Table 4
pH Adjustment Agent Name and Chemical Formula Identifying
Symbol
67.5 % Solution of nitric acid in water a
HNO
40 % Solution of fluorosilicic acid in water b
H SiF
25 % Solution in water of ammonia NH OH c
Surface treatment was performed using the treatment conditions and surface
treatment bath compositions reported in Tables 5 and 6. The amounts of the
reagents
reported in the treatment bath composition columns in Tables 5 and 6 are
values calcu-
lated for the pure reagent. The surface treatment conditions used in
Comparative Ex-
amples 5 to 9 are reported further below.
Comparative Example 1 used a metal acetylacetonate as the only component of
the treatment bath in order to provide a comparative example testing the
formation of a
coating of the metal acetylacetonate alone. Comparative Example 2 used a water-
solu-
ble titanium compound as the only component of the treatment bath in order to
provide
a comparative example testing the formation of a coating of the inorganic
titanium com-
pound alone. Comparative Example 3 employed a treatment bath comprising both
the
water-soluble inorganic titanium compound and the water-soluble inorganic
zirconium
compound in order to provide a comparative example testing the formation of an
inorganic composite coating constituted of titanium and zirconium but lacking
the metal
~s acetylacetonate. Comparative Example 4 was directed to the formation of
coatings with
very low coating weights.
In Comparative Example 5, a 2 % solution in water of a commercial zirconium
phosphate surface treatment agent (ALODINE~ 4040 from Nihon Parkerizing Co.,
Ltd.)
was used to carry out surface treatment. This solution was applied to the
above-de-
scribed AI alloy sheet by spraying for 60 seconds at 50 °C, after which
the corrosion
resistance and paint adherence were evaluated.
In Comparative Example 6, an aqueous solution of a commercial phosphoric acid
chromate surface treatment agent (mixed aqueous solution of 4 % of ALCHROM~
K702SL and 0.3 % of ALCHROM~ K702AC, both from Nihon Parkerizing Co., Ltd.}
was
is used to carry out surface treatment. This solution was applied to the above-
described
AI alloy sheet by spraying for 20 seconds at 50 °C, after which the
corrosion resistance
and paint adherence were evaluated.
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Table 5 - Part A
Ex- Active Treatment
ampleIngredients Conditions
and Their
Concentrations
in g/1
in the
Surface
Treatment
Bath
for This
Exam
le
Num- Metal Titanium ZirconiumpH Adjust-pH Temper-Contact
ber Ace- Source Source went Agent ature, Time,
tylacetonate C Seconds
1 a 1.2 A 0.5 None NoneNone 3.060 120
2 b 0.1 None None a 1.5 c 5.835 300
c 1.0
3 d 20.0 B 10.0 b 1.0 b 2.770 3
4 a 1.0 None None a 3.0 c 4.650 90
a 0.5 A 1.0 a 1.0 a 3.870 60
d 4.0
Table 5 - Part B
ExampleSubstrateCoating Salt Spray CorrosionAdherence, % of
Number Weight, Resistance RatingGrid
mg/m2 Squares Remaining
A1 alloy 290 + + 100
1 Mg alloy 615 + + 99
Zn plating190 + 100
A1 alloy 400 + + 100
2 Mg alloy 1300 + + 100
Zn plating360 + + 99
A1 alloy 185 + 100
3 Mg alloy 680 + + 98
Zn plating190 + 98
A1 alloy 200 + 99
4 Mg alloy 420 + + 100
~
'
Zn plating140 + 98
A1 alloy 780 + + 100
5 Mg alloy 1850 + + 98
Zn plating1120 + + 99
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Table 6 - Part A
Com- Active Treatment
para-Ingredients Conditions
five and Their
Concentrations
in g/t
in the
Surface
Treatment
Bath for
This Comparative
Example
Ex- Metal Ace-Titanium ZirconiumpH Adjust-pH Temper-Contact
ampletylacetonateSource Source ment Agent ature, Time,
Num- C Seconds
ber
1 a 1.0 None NoneNone Noneh and c 4.650 90
2 None None A 5.0 None Nonec 3.040 30
3 None None A 1.0 a 1.0 c 3.870 60
4 a 0.005 A 0.005 None Nonec 5.520 2
None None None NoneNone NoneNone * 50 60
6 None None None NoneNone NoneNone * 50 20
7 None None None NoneNone NoneNone * 40 60
8 None None None NoneNone NoneNone * 95 1800
9 None None None NoneNone NoneNone * 43 120
Tabie 6 - Part B
Compa- Substrate Coating Weight,Salt Spray CorrosionAdherence,
rative mg/mz Resistance Rating %
Example of Grid
Number Squares
Remainin
A1 alto _175 x 98
~
1 M alto 350 ~ 98
Zn latin 110 x 98
A1 allo 185 x 96
2 M allo 240 x 94
Zn latin 120 x 91
A1 allo 400 0 96
3 M alto 630 O 95
Zn Latin 190 x 90
A1 alto 1 x 72
4 M allo 2 x 85
Zn Latin 1 x 79
5 A1 allo 100 x 100
6 A1 alloy Cr : 70 + 100
Al allo Cr : 170 + + 99
7 M allo Cr : 50 + 99
Zn Latin Cr : 70 + + 100
8 M allo Cr: 800 + + 100
9 Zn Latin 4000 x 91
*The pH value for these baths was not reported.
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In Comparative Example 7, a 7 % solution in water of a commercial chromic acid
chromate surface treatment agent (ALCHROM~ 713M from Nihon Parkerizing Co.,
Ltd.)
was used to carry out surface treatment. This solution was applied to the
above-de-
scribed AI alloy sheet, Mg alloy sheet, and Zn-plated steel sheet by dipping
for 60 sec-
s onds at 40 °C, after which the corrosion resistance and paint
adherence were evaluated.
In Comparative Example 8, a treatment bath based on MIL-M-3171C (TYPE III,
with a main component of sodium bichromate) was used for surface treatment.
This
bath was applied to the Mg alloy sheet by dipping for 30 minutes at 95
°C, after which
the corrosion resistance and paint adherence were evaluated.
In Comparative Example 9, after degreasing (1 ) and water rinsing (2) the
workpiece was dipped for 30 seconds at 25 °C in a 0.1 % aqueous
solution of a commer-
cial titanium-based surface conditioner (PREPALENE~ 4040 from Nihon
Parkerizing
Co., Ltd.). This was followed by surface treatment with an aqueous solution of
a
commercial zinc phosphate-based surface treatment agent (mixed aqueous
solution of
~s 5 % of PALBOND~ L3020, 0.5 % of Additive 4813, 2 % of Additive 4856, and 1
% of
Neutralizer 4055, all from Nihon Parkerizing Co., Ltd.). This bath was applied
to the Zn-
plated steel sheet by dipping for 120 seconds at 43 °C, after which the
corrosion
resistance and paint adherence were evaluated.
EVALUATION METHODS
Zo (1) Coating Weight: The coating weight of the entire organic-inorganic
composite
coating was measured using either a fluorescence x-ray analyzer or stripping
by dipping
for 5 minutes at 90 °C in 5 weight % aqueous chromic acid solution.
(2) Corrosion Resistance: The corrosion resistance was evaluated using the
salt
spray test described in JIS Z-2371. The extent of corrosion development on the
surface
2s treated sheet was evaluated visually after the salt spray test and reported
on the
following scale:
+ + ~ area of corrosion less than 10%;
+ - area of corrosion at feast 10%, but less than 30%;
D - area of corrosion at least 30%, but less than 50%;
so x - area of corrosion at least 50%.
The salt spray times for each of the surface-treated samples were:'
For AI alloy sheet 480 hours
For Mg alloy sheet 24 hours
For Zn-plated steel sheet 120 hours
3s (3) Paint Adherence: Paint adherence testing was carried out on the AI
alloy sheet,
Mg alloy sheet, and Zn-plated steel sheet samples after surface treatment
under the
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WO 00/24948 PCT/US99/2398Z
conditions of Examples 1 to 5 and Comparative Examples 1 to 9. The surface of
the
sample was coated to a dry film thickness of 10 micrometres (hereinafter
usually
abbreviated as "pm") with an epoxy resin paint from Kansai Paint Co., Ltd. and
the
sample was then baked for 10 minutes at 200 °C. A grid of 100 squares
(width = 2 mm)
s was subsequently introduced in the center of the painted sheet using a
cutter, after which
the sample was dipped for 60 minutes in boiling deionized water. After this
boiling water
challenge, the painted sheet was air-dried and then subjected to a peeling
test with
cellophane tape. The paint adherence was evaluated on the basis of the number
of grid
squares that were not peeled off.
In this test, a larger number of remaining grid squares is indicative of a
better
paint adherence. A score of 98 or better indicates a satisfactory performance
at the level
of practical application.
The results of the evaluations are reported in Tables 5 and 6. These results
demonstrate that the conversion coatings formed by the surface treatment baths
of the
~s present invention have a corrosion resistance and paint adherence equal to
that of con-
ventional chromate coatings. Moreover, the results in these tables demonstrate
that an
excellent corrosion resistance can be realized by the formation at appropriate
coating
weights of organic-inorganic composite coatings that contain both metal
acetylacetonate
and at least one of titanium and zirconium.
zo
