Note: Descriptions are shown in the official language in which they were submitted.
W093~0926~ PCT/US92/OX811
-~` 2121486
~escri~tion
TREATMENT FOR T~E FORMATION OF A CORR08ION RE8I8TAN~ FILM
ON NETAL 8URFACE8
Technical ~ield
The present invention relates to a novel treatment ag-
ent that forms a strongly corrosion-resistant film on the
surface of metals such as iron, zinc, aluminum, and the
5 like. This film is also an excellent paint undercoat.
ç~ground Art
At present, increasingly hiqh levels of corrosion re-
si~tance are being required of painted objects such as au-
tomobile bodies and construction materials. Metal surfaces
have heretofore been treated by phosphate treatments, chro-
mate treatments, etc.; however, the prior metal surface
treatment agents do not always exhibit a satisfac_ory cor-
rosion~resistance and paint adherence.
The art is already familiar with the formation of a
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phosphate film on a metal surface as a generally applicable
pretreatment method when organic films, e.g., paints, ad-
hesives, and the like, are applied on the su~rfaces of met-
als such as iron, zinc, aluminum, and the like. The cor-
rosion resistance and paint adherence are improved by this
addition of a phosphate film on the metal surface prior to
the application of the organic coating (typically paint3.
When higher levels of corrosion resistance are required,
both a phosphate treatment and a post-treatment (e.~.,
sealing with chromic acid and the like) or primèr appli-
cation are carried out prior to painting. However, these
post-treatments (e.g., sealing with chromic acid and the
like) contribute only minor benefits. Moreover, while the
application of a primer does improve the paintability, this
also expands the painting process and thus substantially
impairs the workability.
Nevertheless, primer application is currently requi~ed
for painted objects such as automobile bodies and construc-
SUBSTITUTE SHEET
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W093~0926~ 2 12 i ~ 8 ~ PCT/US92/08811
tion materials. In the case of automobile bodies, a ~-nc
phosphate film is formed on the metal surface, which i8
then immersed in aqueous paint for electrodeposit~on coat-
ing. This coating operation ls a type of primer coating,
s and its purpose is to increase the corrosion resistance of
the painted surface and to secure corrosion resistance for
the interior surfaces of the automobile body, which can be
difficult to finish coat. A primer coating is similarly
applied on construction materials prior to finish coating
o in order to increase the corrosion resistance.
While improvements in operatinq efficiency and cost
reduction in painting operations require a contraction of
the process, a satisfactory response to this goal has yet
to be developed. Thus, phosphate films alone have a poor
s corrosion resistance, while painting alone does not satisfy
the requirements for corrosion resistance and paint adher-
ence. When higher levels of corrosion resistance are re-
;~ quired, both a phosphate film and a primer coating are re-
quired. This results in high painting costs and reguires
large work areas. The development of a metal surface
treatment agent that exhibits a high corrosion resistance
and paint adherence is therefore desired. The development
of a metal-surface-treatment agent that permits the omis-
sion of primer coating is also desired.
25 Disclosure of_the Invention
~roblems to Be_Solved bY the Invention
As a means of responding to the above-listed problems,
the present invention takes as its object the introduction
of a metal-surface-treatment agent that can impart a high
30 corrosion resistance and paint adherence to metals that are
suitable for phosphate film treatment, such as iron, zinc,
aluminum, and the like (hereinafter briefly denoted simply
as "metal"). A further object of the present invention is
the introduction of a metal surface treatment agent that
35 permits the omission of primer coating while at the same
time retaining the level of corrosion resistance currently
available.
wo g3tog26~ 2 1 2 1 ~ ~ 6 PCI`/IJS92/0881 1
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Summary of the Invention
As the result of extenslve research directed at solv-
ing the aforementioned problems, it has now been discovered
that a high corrosion resistance and palnt adherence are
s obtained by film formation from a phosphate treatment bath
that contains an organic polymeric compound (or salt there-
of) having certain properties. The present invention was
developed as a result of this discovery.
That 18, a film that exhibits the highly desirable
o properties specified above can be formed by treating the
metal surface with a treatment agent for the formation of
;~ a film on metal surfaces, wherein said treatment agent
characteristically compri~es a phosphate surface treatment
bath ~hich contains a cationic organic polymeric compound
s (or salt thereof) that contains at least 1 cationic nitro-
gen atom and has a molecular weight of 1,000 to 1,000,000.
The film according to the present invention preferably is
a composite film in which the resin composed of the cation-
~ ic organic compound (or salt thereof) has penetrated into
-~ ~ the grain boundaries between phosphate crystals with an
accompanying formation of a phosphate crystal/resin com-
posite.
The surface treatment agent according~to the present
invention comprises the solution or stable dispersion of a
s cationic organic polymeric compound (or salt thereof) i~ a
phosphate treatment bath. Said phosphate treatment bath
comprises any surface-treatment bath that is capable of
forming a phosphate film on the surface of a metal such as
iron, zinc, aluminum, etc., either for a single species of
30 metal alone or simultaneously on the surfaces of two or
more species of the preceding metals. In general, its es-
sential components are zinc ions and phosphate ions, but it
may optionally contain nitrate ions, other metal ions
(nickel, manganese, calcium, and the like), fluoride, and
3s various types of oxidants. However, the phosphate treat-
ment bath is not specifically restricted within the context
of the present invention, and the present invention encom-
wo g3/0926:~ 2 1 2 1 4 8 6 PCr~lS92/0881 .
passes all known phosphate treatment baths.
The cationic organic polymeric compound should contain
at least 1 cationic nitrogen atom and should have a molecu-
lar weight of 1,000 to 1,000,000. Although its structure
is not restricted in the broadest embodiments of the inven-
tion, organic polymers are particularly preferred that have
a resin skeleton comprising at least one selection from
epoxy resins, urethane resins, polybutadiene resins, acryl-
ic resins, and maleic anhydride resins, wherein these
o resins contain a cationic nitrogen-containing group.
The salts of the cationic organic polymeric compound
encompass its inorganic salts and organic salts. The inor-
ganic salts are exemplified by phosphate, nitrate, sulfate,
and the like, and the organic salts are exemplified by ace-
tate, propionate, glyconate, and the like. A single spe-
cies or two or more species of this cationic organic poly-
meric compound (or salt thereof) can be employed. Only a
weak improvement in corrosion resistance is obtained at
molecular weights below 1,000, while it is very difficult
to obtain dissolution or stable dispersion in zinc phos-
phate baths at molecular weights in excess of 1,000,000.
Noreover, paint additives (such as pigment and the
like), other types of resins, activators, and the like may
be added on an optional basis.
With respect to the technique for treating the metal
surface, the present invention can employ conversion treat-
ment ~y spray or immersion as well as electrolytic metho-
dologies, and the treatment agent according to the present
invention is not limited to a particular treatment method.
Examples
The effects of the present invention will be explai-ned
in detail in the following using illustrative examples and
comparison examples; however, the present invention is not
limited to the examples, which describe merely a typical
3s pre-paint phosphate treatment and a typical painting sys-
tem. In comparison examples, evaluation and treatment were
conducted as in the examples, but with the use of organic
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W093/0926~ 2 1 2 1 ~ ~ e PCT/US92/088t1
polymeric compound outside the scope of t~e present inven-
tion and with omission of the cationic organic polymer
altogether.
The general conditions for the examples and comparison
s examples were as follows:
WorkDieces: Cold-rolled steel sheet; electroplated steel
sheet ~zinc coating z 20 g/m2); aluminum sheet (JIS 5052).
Surface treatment agents: The cationic organic polymeric
compounds used in the examples and the polymeric compounds
~; lo used in t~e comparison examples are reported in Table 1.
PARBOND~M L3020 (surface-treatment agent for automotive
applications from Nihon Parkerizing Company, Limited) was
used for the organic`polymer-free phosphate surface treat-
, ment bath. This was a typical phosphate surface-treatment
`~ 1s bat~.
Treatment sequence:
1) Degreasing: 2 % solution of FINECLEANERTH L4460 (from
~ Nihon Parkerizing Company, Ltd.), 120 second spray at
`~ 42 C
2) Water wash: 30 second spray at room temperature
3) Surface conditioning: 0.1 % solution of PARCOLENETM ZN
(from Ni~on Parkerizing Company, Ltd.), 20 second
spray at room temperature
;~ 4) The surface-treatment agents accordi~g to the present
- ~ 25 invention and the surface-treatment agents in the c~m-parison examples were both applied under the following
conditions: immersion at 42 C for 120 seconds.
5) Water wash: 30 second spray at room temperature
6) Wash with deionized water (conductivity, 0.2 mi-
: 30 crosiemens/cm): 20 second spray at room temperature
After completion of the six process steps noted above
and drying, painting was conducted by the following pro-
cesses (the primer step was sometimes omitted, as noted in
the tables below):
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W093/0926~ 2 1 2 1 ~ 8 6 P~ S92/0881 1
Table 1
Designa- Chemical Nature of the organic Molecular
tion of PolYmeric Compound Used Weiaht
s Treatment
A adduct of HN(CH3)2 with bisphenol A8,800
epoxy resin
B copolymer of methyl methacrylate20,000
o and dimethylaminoethyl methacrylate
C adduct of H2NCH2N(CH3)2 with maleic2,000
anhydr~de resin
a adduct of H2NCH2N~CH3)2 with maleic800
maleic anhydride resin
b polyvinyl alcohol 3,000
1) Primer coating: Electrodeposition painting with ELE-
CRONTM 9410 from Kansai Paint Kabushiki Kaisha to pro-
duce a film thickness = 20 micrometers; baking at 175
.
: 20 C for 30 minutes
2) Intermediate coating: XPX36 from Kansai Paint Kabu-
shiki Kaisha; fllm thickness = 30 micrometers; baking
at~140 C for 30 minutes
3~) Finish coating: RUGABAKE~M B 531 from Xans~i Paint Ka-
bushiki-Kaisha; film t~ickness 40 micrometers; baking
at 140 C for 30 minutes.
All the process steps noted above were carried out in
the same manner for both the examples and tbe compari~on
examplas, except for the chemical nature of the surface-
treatment agents used (in step 4).
Performance evaluation:
1) Water-resistant secondary adhesion: The painted sheet
was immersed in deionized water at 40 C for 240
hours, and a checkerboard of 100 squares (2 mm x 2 mm)
was scribed into the base material using a sharp cut-
~; ter. After peeling with cellophane tape, the number
of peeled squares was counted. A smaller number of
peeled squares indicates a better score.
2) Composite cycle test: A cross was scribed in the
o painted sheet throuqh to the base material, using a
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W093/0926~ 2 1 2 1 ~ 8 6 PCT/US92/08811
sharp cutter, and the painted sheet was then subjected
to 14 repetitions of the Tl - T2 cycle (see below).
After the test, evaluation was carried out by measur-
ing the maximum one side film blister width from the
s inscribed cross.
Tl : salt-spray test (JIS Z 2371) : 24 hours
T2 : wetting test (50 C, 70 % RH) : 216 hours
~enefits of the Invention
Tables 2, 3, and 4 report the paint adherence and cor-
~ 10 rosion resistance of the films o~tained by surface treat-
-~ ; ment, re~pectively, of cold-rolled ~teel ~heet, electrogal-
vanized ~teel sheet, and aluminum sheet. These tables also
include the results for the comparison examples~
In the case of treatment by a metal-surface-treatment
~s agent for composite film formation in accordance with the
pre~ent invention, the results confirm a remarkable im-
provement in corrosion resistance and paint adherence over
phos p ate treatment. In addition, even with omission of
primer~ coating, the present invention exhibits a perform-
ance approximately equivalent to the application of a pri-
mer coat on phosphate film.
When an organic polymeric compound was used that was
not within the scope of the present invention, either æub-
stantially no effect was obtained or the performance was in
fact degraded.
As discussed hereinbefore, the metal surface treatment
agent for composite film formation in accordance with the
invention increases the corrosion resistance and paint ad-
herence and makes possible the omission of primer coating.
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wo g3/0926~ 2 1 2 1 4 8 ~ PCT/US92/08811
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Table 2 I
Example Organic Polymer Primer Water Compos-
("Ex") Component Coating Resist- ite
or Com- Used? ant Cycle
parison Secon- Test:
Example dary Blister
("CE") TypeConcen- Adhe- Width
Number tration sion: in mm
Number
Peeled _
¦Ex 1 A~ 0.1 % yes 0 < 0.5
Ex 2 ~ 0.5 % yes 0 S 0.5
: Ex 3 2.0 ~ yes < o.~
_ I
: . Ex 4 A1.0 % no 0 1.7
, CE 1 na ne yes 0 1.5
.; ~ CE 2 none ~ no 57 4.4
CE 3 a ¦ 1.0 % ~ yes 0 1.4
CE 4 b ¦ 1.0 % yes 37 1.7
~ . ....
. Table 3
Example Organic Polymer Primer Water Compos-
( nEx~l ) Component Coating Resist- ite
: or Com- Used? an~ Cycle
parison Secon- Test:
: ~ Example . _ dary Blister
. ¦ ("CE") Type Concen- Adhe- Width ,
.Number tration sion: in mm
. Number
. Peeled ~
Ex s A 0.1 % yes 0 < 0.5
. _
Ex 6 B 0.5 % yes 0 ~ 0.5
.
Ex 7 C 2.0 % yes 0 < 0.5
Ex 8 A 1.0 % no 1.2.
CE 5 nc ne yes 0 1.0
CE 6 none no 36 2.2
CE 7 a 1.0 % yes 0 1.1
CE 8 b 1.0 % yes 17 1.8
:~ 8
~ ;~ SUBSTITUTE SHEET
W093/0926~ 2 1 2 1 ~ 8 ~6 PCT/~S92/08811
~,
Table 4 . I
- ._
Example Organic Polymer Primer Water Compo~-
("Ex") Component Coating Resist- lte
or Com- Used? ant Cycle
parison Secon- Test:
Example dary Blister
("CE") Type Concen- Adhe- Width
Number tration sion: in mm
Number
Peeled
Ex 9 A 0.1 % yes 0 S 0.5
Ex 10 B 0.5 % yes S 0.5
Ex 11 C 2.0 % yes 0 S 0.5
Ex 12 A 1.0 % no 6 0.7
~: CE 9 none yes 5 0.8
:: ~ CE 10 none no 36 1.5
CE 11 a 1.0 t yes _ 4 0.8
CE 12 b 1.0 % yes 17 1.2
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