U.S. patent application number 09/833070 was filed with the patent office on 2001-12-13 for nonchromate rust preventive agent for aluminum, method of rust prevention and rust-preventive aluminum prdoducts.
This patent application is currently assigned to Nippon Paint Co., Ltd.. Invention is credited to Inbe, Toshio, Takahashi, Masashi, Yamasoe, Katsuyoshi.
Application Number | 20010050029 09/833070 |
Document ID | / |
Family ID | 18630120 |
Filed Date | 2001-12-13 |
United States Patent
Application |
20010050029 |
Kind Code |
A1 |
Inbe, Toshio ; et
al. |
December 13, 2001 |
Nonchromate rust preventive agent for aluminum, method of rust
prevention and rust-preventive aluminum prdoducts
Abstract
The present invention has its object to provide a nonchromate
rust preventive agent for aluminum which, despite its being of the
nonchromate type, is capable of affording sufficient corrosion
resistance and, even when applied to the material for
heat-exchanger fins, for instance, does not allow development of
white rust. This invention provides a nonchromate rust preventive
agent for aluminum which comprises a zirconium compound, a fluoride
ion, a water-soluble resin and an aluminum salt and an aluminum
product as obtainable by a rust preventive treatment using said
nonchromate rust preventive agent.
Inventors: |
Inbe, Toshio; (Kanagawa,
JP) ; Takahashi, Masashi; (Tokyo, JP) ;
Yamasoe, Katsuyoshi; (Chiba, JP) |
Correspondence
Address: |
SHANKS & HERBERT
TransPotomac Plaza
Suite 306
1033 N. Fairfax Street
Alexandria
VA
22314
US
|
Assignee: |
Nippon Paint Co., Ltd.
|
Family ID: |
18630120 |
Appl. No.: |
09/833070 |
Filed: |
April 12, 2001 |
Current U.S.
Class: |
106/14.44 |
Current CPC
Class: |
C23C 22/34 20130101;
C09D 5/084 20130101 |
Class at
Publication: |
106/14.44 |
International
Class: |
C09D 005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 20, 2000 |
JP |
2000-119081 |
Claims
1. A nonchromate rust preventive agent for aluminum which comprises
a zirconium compound, a fluoride ion, a water-soluble resin and an
aluminum salt, the concentration of said zirconium compound being
100 to 100000 ppm as zirconium ion, the concentration of said
fluoride ion being 125 to 125000 ppm, the concentration of said
water-soluble resin being 100 to 100000 ppm on a nonvolatile matter
basis, and the concentration of said aluminum salt being 10 to
10000 ppm as aluminum ion.
2. The nonchromate rust preventive agent for aluminum according to
claim 1 wherein a fluorozirconic acid and/or an ammonium
fluorozirconate are/is used as said zirconium compound.
3. The nonchromate rust preventive agent for aluminum according to
claim 1 or 2 wherein said water-soluble resin has a functional
group capable of binding to a zirconium compound and/or aluminum in
film formation.
4. A method for nonchromate rust prevention of aluminum which
comprises treating an aluminum substrate with the nonchromate rust
preventive agent according to any of claims 1 to 3 to form the film
in the weight range of 10 to 1000 mg/m.sup.2 in terms of
zirconium.
5. An aluminum product as obtainable by a rust preventive treatment
using the nonchromate rust preventive agent according to any of
claims 1 to 3.
Description
FIELD OF THE INVENTION
[0001] The present invention relates to the nonchromate rust
prevention of aluminum and more particularly to a nonchromate rust
preventive agent suited to the treatment of aluminum sheeting in a
coil form, a method of rust prevention and a rust-preventive
aluminum product.
BACKGROUND OF THE INVENTION
[0002] The rust prevention of aluminum or aluminum alloy has
heretofore been made by spraying or dipping using a reactive
chromate or phosphate-chromate agent or a coating-type chromating
agent. In the field of such chromating agents, there have been
developed those which are comparatively environment-benign through
contrivances such as film weight reduction or replacement of the
harmful hexavalent chromium with the low-toxicity trivalent
chromium. However, the risk for environmental contamination at
waste disposal cannot be said to be nil.
[0003] On the other hand, with regard to the nonchromate reactive
type treating agent and coating type treating agent, Japanese
Kokoku Publication Sho-55-38997, for instance, discloses an acidic
cleaning agent comprising polyacrylic resin and zirconium fluoride,
among other components. Further, Japanese Kokai Publication
Hei-4-232281 discloses an aqueous acidic solution comprising an
anionic acrylic acid-acrylamide copolymer, zirconyl ammonium
fluoride and nitric acid. Japanese Kokai Publication Hei-11-106954
discloses an acidic treating composition comprising a water-soluble
phenolic resin, a zirconium or other metal-containing compound, a
silane coupling agent, and hydrofluoric acid, phosphoric acid
and/or acetic acid.
[0004] However, the corrosion resistance imparted by the
nonchromate type treating agents disclosed in the above patent
publications is invariably poor as compared with that provided by
chromate type treating agents and has not satisfied practical
needs. The object of the present invention is to provide a
nonchromate rust preventive agent for aluminum which, despite its
being of the nonchromate type, is capable of affording sufficient
corrosion resistance and, even when applied to the material for
heat-exchanger fins, for instance, does not allow development of
white rust. A further object is to provide a method of rust
prevention and a rust-preventive aluminum product.
SUMMARY OF THE INVENTION
[0005] The nonchromate rust preventive agent for aluminum according
to the present invention comprises a zirconium compound, a fluoride
ion, a water-soluble resin and an aluminum salt,
[0006] the concentration of said zirconium compound being 100 to
100000 ppm as zirconium ion,
[0007] the concentration of said fluoride ion being 125 to 125000
ppm,
[0008] the concentration of said water-soluble resin being 100 to
100000 ppm on a nonvolatile basis,
[0009] and the concentration of said aluminum salt being 10 to
10000 ppm as aluminum ion.
[0010] The fluoride ion concentration, when a fluorozirconium
compound is used as said zirconium compound, represents the sum of
the concentration derived from the fluorine compound and the
concentration derived from the fluorozirconium compound.
[0011] As said zirconium compound, a fluorozirconic acid and/or an
ammonium fluorozirconate may be used.
[0012] Moreover, said water-soluble resin preferably has a
functional group capable of binding to said zirconium compound
and/or aluminum in film formation.
[0013] The method of nonchromate rust prevention according to the
present invention comprises treating an aluminum substrate with
said rust preventive agent to form the film in the weight range of
10 to 1000 mg/m.sup.2 in terms of zirconium.
[0014] The rust-preventive aluminum product of the present
invention is obtainable by a nonchromate rust preventive treatment
using said rust preventive agent.
DETAILED DESCRIPTION OF THE INVENTION
[0015] The present invention is now described in detail.
[0016] As mentioned above, the nonchromate rust preventive agent of
the invention comprises a zirconium compound, a fluoride ion, a
water-soluble resin and an aluminum salt.
[0017] The above zirconium compound is a cardinal component capable
of binding to the aluminum (inclusive of aluminum alloy; the same
applies hereinafter) surface etched by the fluoride ion to form a
rust preventive layer and, at the same time, binding to and curing
the water-soluble resin to insure formation of a tough resin film.
As examples of such zirconium compound, there can be mentioned
fluorozirconic acid, the lithium, sodium, potassium and ammonium
salts of fluorozirconic acid, zirconium sulfate, zirconyl sulfate,
zirconium nitrate, zirconyl nitrate, zirconium fluoride and
zirconium carbonate, among others.
[0018] These zirconium compounds can be used singly or in a
combination of two or more species. The preferred concentration of
the zirconium compound in the rust preventive agent is 100 to
100000 ppm as zirconium ion, the range of 1000 to 10000 ppm being
still more preferred. When the zirconium ion concentration is less
than 100 ppm, corrosion resistance and adhesion to the hydrophilic
coating film to be used for heat-exchanger fins tend to be
decreased. On the other hand, formulating the zirconium compound in
excess of 100000 ppm will not be rewarded with any further
improvement in performance but rather increases the cost of
production.
[0019] The fluoride ion mentioned above can be supplied by using,
for example, hydrofluoric acid, ammonium fluoride, ammonium
hydrogen fluoride, sodium fluoride, sodium hydrogen fluoride or the
like. When a fluorine-containing zirconium compound, such as
fluorozirconic acid and ammonium fluorozirconate, is used as the
zirconium ion donor, the fluoride ion is partly supplied from such
a compound. The fluoride ion concentration of the rust preventive
agent is preferably 125 to 125000 ppm, more preferably 1250 to
12500 ppm. The fluoride ion concentration referred to above is the
concentration of the fluoride ion present in free state in the rust
preventive solution and can be measured by using an instrument
having a fluoride ion electrode, for instance. When the fluoride
ion concentration is lower than 125 ppm, the degree of etching of
the aluminum surface is insufficient so that no adequate rust
preventive film may be constructed. Exceeding 125000 ppm is not
rewarded with any further improvement in performance but rather
increases the cost burden. The zirconium-fluorine ratio, Zr/F, is
preferably 0.5 to 0.9 by weight, more preferably 0.6 to 0.8 by
weight. Above or below this range, no sufficient corrosion
resistance is obtained.
[0020] The above water-soluble resin preferably has a functional
group, such as carboxyl, hydroxyl, sulfo, amino or the like, which
is capable of binding to the zirconium compound and/or aluminum
substrate in film formation. As examples of such water-soluble
resin, the following can be mentioned.
[0021] (a) Unsaturation-polymerizable water-soluble polymers having
carboxyl and/or hydroxyl groups, such as poly (meth) acrylic acid,
(meth) acrylic acid- (meth) acrylate copolymers,
styrene-(meth)acrylic copolymers, polyvinyl alcohol obtainable by
partial saponification of polyvinyl acetate resin,
polyvinylpyrrolidone, and polymers of (meth)acrylamide derivatives
such as N-methylolated (meth)acrylamide.
[0022] (b) Naturally-occurring macromolecular compounds having
carboxyl and/or hydroxyl groups as well as their derivatives, for
example cellulose derivatives such as carboxymethylcellulose (CMC),
hydroxyethylcellulose (HEC), hydroxypropylcellulose (HPC),
methylcellulose (MC), ethylcellulose (EC),
ethylhydroxyethylcellulose (EHEC), etc., methylcellulose
derivatives and their sodium, potassium and ammonium salts, among
others.
[0023] (c) Water-soluble polyester resins, for example the
water-solubilized resin obtainable by half-esterification of the
hydroxyl group of a polyester resin with trimellitic anhydride and
neutralization of the residual carboxyl group with an amine or the
like and the water-soluble resin obtainable by reacting
polyethylene glycol with a polybasic acid.
[0024] (d) Water-soluble epoxy resins, for example water-soluble
epoxy resins such as di- or polyglycidyl ethers of aliphatic
polyhydric alcohols, diglycidyl esters of dicarboxylic acids,
nitrogen-containing heterocycle-containing epoxy compounds, etc.
and water-dispersible epoxy resins obtainable by dispersing or
emulsifying epoxy resins in water or a water-organic solvent
mixture with the aid of an emulsifier or modifying epoxy resins so
as to make them water-soluble or water-dispersible and
emulsifiable.
[0025] (e) Water-soluble polyurethane resins, for example the
polyurethane resin solubilized by introducing an anionic or
cationic group into the molecule, the resin obtainable by causing a
bisulfite to be added to the terminal isocyanato group of a
urethane prepolymer to block the isocyanato group and rendering it
water-soluble by taking advantage of the hydrophilicity of the
sulfonate, and the resin obtainable by blocking a urethane
prepolymer with a blocking agent and emulsifying or dispersing the
same by force.
[0026] (f) Water-soluble phenolic resins, such as polycondensation
products of phenolic hydroxyl-containing compounds, such as phenol,
xylenol, p-alkylphenols, p-phenylphenol, chlorophenol, bisphenol A,
phenolsulfonic acid, resorcinol, etc., with an aldehyde, such as
formaldehyde, furfural or the like. These are generally known as
phenol-formaldehyde resin, cresol-formaldehyde resin,
phenol-furfural resin, resorcinol resin and so on.
[0027] (g) Water-soluble amino resins, for example melamine resins
such as n-butylatedmelamine resin, isobutylatedmelamine resin,
etc., urea resins and other resins, which have been rendered
water-soluble.
[0028] The water-soluble resins mentioned above may be used singly
or two or more of them may be used in combination. The
concentration of the water-soluble resin in the rust preventive
agent of the invention is preferably 100 to 100000 ppm, more
preferably 1000 to 10000 ppm, on a nonvolatile matter basis. When
the resin concentration is lower than 100 ppm, corrosion resistance
and water resistance tend to be inadequate. On the other hand,
exceeding 100000 ppm will not be rewarded with any further
improvement in performance but rather increase the cost burden.
[0029] The concentration of the aluminum salt in the rust
preventive agent of the invention is preferably in the range of 10
ppm to 10000 ppm, more preferably 100 to 5000 ppm, in terms of
aluminum ion. As examples of the aluminum salt that can be used,
there can be mentioned aluminum nitrate, aluminum sulfate, aluminum
fluoride, aluminum oxide, alum, aluminum silicate, aluminates such
as sodium aluminate, and fluoroaluminates such as sodium
fluoroaluminate. When the concentration of aluminum ion is less
than 10 ppm, the curing reaction of the film may not be
sufficiently promoted so that corrosion resistance will be
inadequate. On the other hand, when it exceeds 10000 ppm, the
curing reaction of the film is hindered and a sludge tends to be
formed in the treating solution.
[0030] In the coating-type rust preventive agent according to the
invention, the fluoride ion etches the aluminum substrate during
the time following application of the composition till the film
dries so that the zirconium is bound to the etched surface to form
a rust preventive layer and, at the same time, acts on the resin as
well to assist in the formation of a resin layer. In the course, it
is supposed that the aluminum ion supplied from the aluminum salt
appears to increase the reactivity of zirconium with the resin to
thereby facilitate formation of a rust preventive film.
[0031] Furthermore, when a coating-type rust preventive agent
containing a zirconium compound as a rust inhibitor is caused to
cure and form a film, the water-soluble resin and zirconium bind to
each other and form a film so that the fluoride ion tends to be
left alone and redundant so that the corrosion resistance tends to
be adversely affected. However, if the fluoride ion concentration
in the treating agent is nil or too low, the reaction between the
aluminum substrate and zirconium will be so retarded that no
sufficient corrosion resistance may be obtained by the coating-type
rust preventive agent. In the rust preventive agent of the present
invention, an aluminum ion is supplied from an aluminum salt, with
the result that, in the course of formation of a rust preventive
film, the aluminum ion captures the excess of fluoride ion to form
fluoroaluminum. It is likely that the above mechanism is involved
in the enhancement of corrosion resistance.
[0032] In the rust preventive agent of the present invention,
various additives may also be formulated in suitable amounts. As
such additives, there can be mentioned aluminum sludge inhibitors
such as tannic acid, imidazole, etc.; reaction-accelerating
oxidizing agents such as hydrogen peroxide, molybdic acid, etc.;
resin curing agents such as metal oxides, phenolic resin, etc.; and
bath-stabilizing chelating agents.
[0033] In the method for nonchromate rust prevention according to
the invention, the above rust preventive agent is used to form a
rust preventive film on an aluminum sheet or a shaped article of
aluminum. The aluminum sheet includes the precoated sheet and foil
supplied in the coil form. The shaped article of aluminum includes
aluminum cans for beverages, aluminum wheels and other
castings.
[0034] For rust-preventing the aluminum sheet, the sheet is
degreased in advance where necessary and the rust preventive agent
of the invention is applied. This application can be made with a
bar coater or a roll coater. An alternative method comprises
dipping the sheet in a bath of the rust preventive agent and
wringing out the surplus agent with a squeeze-roll. For the
treatment of a shaped article of aluminum, it is recommendable to
use the method which comprises dipping the article in the bath and
subjecting it to centrifugation or the air-curtain coating method.
When the dipping method is used, the rust preventive treatment bath
is supplied with aluminum ion from the aluminum substrate as well.
Therefore, the aluminum ion concentration should be maintained
within the above-mentioned range by adjusting the aluminum salt
content of the bath refill.
[0035] The coating amount of the rust preventive agent should be
equivalent to a film weight of 10 to 1000 mg/M.sup.2, preferably 10
to 300 mg/m.sup.2, as zirconium. When the film weight is less than
10 mg/m.sup.2, both corrosion resistance and water resistance are
inadequate. On the other hand, exceeding 1000 mg/M.sup.2 will not
be rewarded with any further improvement in performance but rather
cause an economic disadvantage. The aluminum is finally dried by
heating at 70 to 150.degree. C. for 10 seconds to 1 minute.
[0036] The aluminum product according to the invention, as treated
for rust prevention by the above method, carries a rust preventive
film equivalent to 10 to 1000 mg/m.sup.2 of zirconium. When the
rust-preventive aluminum product is a sheet, it can be subjected to
a hydrophilic treatment and used with advantage in such
applications as heat-exchanger fins.
[0037] The rust preventive agent of the present invention is
formulated to contain an aluminum salt so that, when it is applied
for rust prevention, aluminum ions will be available in the system.
As a result, the reactivity between zirconium and resin is promoted
to facilitate formation of a rust preventive film. Therefore, the
composition provides high degrees of corrosion resistance and rust
inhibition fully emulating those provided by the conventional
chromating agents.
[0038] The aluminum product of the invention as treated with the
rust preventive agent of the invention can substitute the
chromating agent as mentioned above so that it finds application in
a broad field. Particularly, it is very suited to the treatment of
aluminum sheeting in the form of a coil for use as the material of
heat-exchanger fins.
EXAMPLES
[0039] The following examples and comparative examples illustrate
the invention in further detail.
Example 1
[0040] Preparation of a Rust Preventive Agent
[0041] A nonchromate coating-type rust preventive agent containing
5000 ppm, as Zr, of fluorozirconic acid, 15000 ppm, on a
nonvolatile matter basis, of polyacrylic acid and 1000 ppm, as Al
ion, of aluminum nitrate in pure water was prepared.
[0042] Rust prevention
[0043] An aluminum sheet (Al 100) for heat-exchanger fin use was
provided. First, this sheet was sprayed with a degreasing agent of
1 mass % concentration (Surf Cleaner 340, Nippon Paint) at
70.degree. C. for 5 seconds, rinsed and dried. Then, the above rust
preventive agent was applied with a bar coater and baked at
120.degree. C. for 20 seconds to prepare a test sheet for
evaluation. The film weight was controlled by adjusting the size of
the bar coater, using #10 as the standard.
[0044] Methods for Evaluation
[0045] <Salt Spray Test>
[0046] The 5% salt spray test (360 hr) was performed in accordance
with JIS Z 2371 and, after the exposure, the corrosion rate of the
test sheet was investigated. Each figure in Table 1 was obtained by
estimating the rusted surface area of the test sheet
macroscopically and rating the finding on a 10-point scale (the
higher the figure is, the lower is the corrosion rate).
[0047] <Moisture Resistance Test>
[0048] A moisture resistance test (360 hr) was performed in an
atmosphere of 50.degree. C., RH >98% and, after the exposure,
the corrosion rate of the test sheet was evaluated. Each figure in
Table 1 was obtained by estimating the rusted surface area of the
test sheet macroscopically and rating the finding on a 10-point
scale (the higher the figure is, the lower is the corrosion
rate).
Examples 2 to 8, Comparative Example 1 to 4
[0049] Except that the amount and kind of zirconium compound, the
amount of hydrofluoric acid, kind and amount of water-soluble
resin, kind and amount of aluminum salt and/or film weight of
zirconium were varied, test sheets were prepared as in Example 1
and evaluated similarly. The formulations and results of evaluation
are shown in Table 2.
1TABLE 1 Example 1 2 3 4 5 6 7 8 Zr. Species A A A B A A A A
Compound ppm.sup.1* 3000 100 100000 2000 3000 3000 3000 3000 F ion
conc. (ppm) 3750 125 125000 2500 3750 3750 3750 3750 Water- Species
D D D E D D D D soluble ppm 15000 100 100000 4000 15000 15000 15000
15000 resin Al salt Species F F F G F F F F ppm.sup.2* 1000 10
10000 500 1000 1000 1000 1000 Additive Kind -- -- -- -- Tannic
Hydrogen Phenolic Gluconic acid peroxide resin acid ppm -- -- -- --
1000 500 1000 100 Zr film weight 100 10 1000 60 100 100 1000 100
(mg/m.sup.2) Salt spray test 10 8 10 10 10 10 10 10 Moisture 10 10
10 10 10 10 10 10 resistance test *.sup.1as Zr *.sup.2as Al A
Fluorozirconic acid, B Ammonium fluorozirconate, C Zirconyl
ammonium carbonate, D Poly(acrylic acid), E Poly(vinyl alcohol), F
Aluminum nitrate, G Aluminum sulfate
[0050]
2 TABLE 2 Compar. Ex. 1 2 3 4 Zr compound Species -- A A C
ppm*.sup.1 0 3000 3000 3000 Hydrofluoric acid 2500 3750 3750 0
(ppm) Water- soluble resin Species D -- D D ppm 15000 0 15000 15000
Aluminum salt Species F F -- F ppm*.sup.2 1000 1000 0 1000 Additive
Kind -- -- -- -- ppm -- -- -- -- Zr film weight 0 100 100 100
(mg/m.sup.2) Salt spray test 1 3 2 2 Moisture resistance 1 3 2 2
test
[0051] It will be apparent from Table 1 that the test sheets
treated with the rust preventive agents of the examples were
superior in the corrosion resistance evaluated by the salt spray
test and lower in the corrosion rate determined by the moisture
resistance test.
* * * * *