U.S. patent application number 11/108880 was filed with the patent office on 2005-09-22 for coating composition for forming titanium oxide film, process for forming titanium oxide film and metal substrate coated with titanium oxide film.
This patent application is currently assigned to KANSAIPAINT CO., LTD.. Invention is credited to Akui, Jun, Haruta, Yasuhiko, Isozaki, Osamu, Nagai, Akinori.
Application Number | 20050205165 11/108880 |
Document ID | / |
Family ID | 26624189 |
Filed Date | 2005-09-22 |
United States Patent
Application |
20050205165 |
Kind Code |
A1 |
Akui, Jun ; et al. |
September 22, 2005 |
Coating composition for forming titanium oxide film, process for
forming titanium oxide film and metal substrate coated with
titanium oxide film
Abstract
The present invention provides a coating composition for forming
a titanium oxide film, comprising (A) a specific
titanium-containing aqueous liquid and (B) at least one compound
selected from the group consisting of organic acids and their
salts. The present invention also provides a process for forming a
titanium oxide film using the coating composition, and a metal
substrate coated therewith.
Inventors: |
Akui, Jun; (Hiratsuka-shi,
JP) ; Nagai, Akinori; (Hiratsuka-shi, JP) ;
Haruta, Yasuhiko; (Hiratsuka-shi, JP) ; Isozaki,
Osamu; (Hiratsuka-shi, JP) |
Correspondence
Address: |
ARMSTRONG, KRATZ, QUINTOS, HANSON & BROOKS, LLP
1725 K STREET, NW
SUITE 1000
WASHINGTON
DC
20006
US
|
Assignee: |
KANSAIPAINT CO., LTD.
Amagasaki-shi
JP
|
Family ID: |
26624189 |
Appl. No.: |
11/108880 |
Filed: |
April 19, 2005 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11108880 |
Apr 19, 2005 |
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10492210 |
Apr 22, 2004 |
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10492210 |
Apr 22, 2004 |
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PCT/JP02/10773 |
Oct 17, 2002 |
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Current U.S.
Class: |
148/247 ;
148/250; 428/472.2 |
Current CPC
Class: |
C01G 23/053 20130101;
C23C 26/00 20130101; C23C 30/00 20130101; C23C 18/1241 20130101;
C09C 1/3607 20130101; C23C 18/1254 20130101; C23C 18/1216 20130101;
C01G 23/04 20130101; C01P 2004/84 20130101; C09D 1/00 20130101 |
Class at
Publication: |
148/247 ;
148/250; 428/472.2 |
International
Class: |
C23C 022/07 |
Foreign Application Data
Date |
Code |
Application Number |
Oct 30, 2001 |
JP |
2001-331919 |
Dec 25, 2001 |
JP |
2001-390786 |
Claims
1. A coating composition for forming a titanium oxide film;
comprising: (A) a titanium-containing aqueous liquid obtained by
mixing at least one titanium compound selected from the group
consisting of titanium hydroxide and its condensates having a
condensation degree of 2 to 30, with aqueous hydrogen peroxide; and
(B) at least one compound selected from the group consisting of
organic phosphoric acids and their salts.
2. A coating composition according to claim 1, wherein the compound
(B) is at least one compound selected from the group consisting of
hydroxyl-containing organic phosphorous acids, carboxyl-containing
organic phosphorous acids and salts of these acids.
3. A coating composition according to claim 1, wherein the
proportion of the compound (B) is 1 to 400 parts by weight per 100
parts by weight of the solids in the titanium-containing aqueous
liquid (A).
4. A coating composition according to claim 1, which is an aqueous
liquid having a pH of 1 to 10.
5. A coating composition according to claim 4, which is an aqueous
liquid having a pH of 1 to 9.
6. A coating composition according to claim 1, which further
comprises an inorganic phosphoric acid compound.
7. A coating composition according to claim 1, which further
comprises at least one halide selected from the group consisting of
titanium halides, titanium halide salts, zirconium halides,
zirconium halide salts, silicon halides and silicon halide
salts.
8. A coating composition according to claim 1, which further
comprises an aqueous organic compound selected from the group
consisting of epoxy resins, phenol resins, acrylic resins, urethane
resins, polyvinyl alcohol resins, polyoxyalkylene chain-containing
resins, olefin-polymerizable unsaturated carboxylic acid copolymer
resins, nylon resins, polyglycerin, carboxymethyl cellulose,
hydroxymethyl cellulose, and hydroxyethyl cellulose.
9. A process for forming a titanium oxide film, comprising applying
a coating composition according to claim 1 to a metal substrate,
followed by drying.
10. A coated metal substrate comprising a metal substrate and a
film of a coating composition according to claim 1 formed on a
surface of the substrate.
11. A coated metal substrate according to claim 10, wherein the
film has a dry weight of 0.001 to 10g/m.sup.2.
12. A coated metal substrate according to claim 10, wherein the
metal substrate is made of steel.
13. A coated metal substrate according to claim 10, wherein the
metal substrate is made of aluminum or an aluminum alloy.
Description
TECHNICAL FIELD
[0001] The present invention relates to a novel coating composition
for forming a titanium oxide film, process for forming a titanium
oxide film, and metal substrate coated with a titanium oxide
film.
BACKGROUND ART
[0002] Metal substrates such as steel sheets, aluminum and aluminum
alloys are usually subjected to various types of surface treatment
(undercoating) to improve the corrosion resistance, processability,
etc.
[0003] In recent years, surface-treated steel sheets are required
to have higher corrosion resistance, and therefore zinc-based metal
plated steel sheets are frequently used as substrates replacing
cold rolled steel sheets.
[0004] Conventionally, chromate treatment or phosphate treatment is
employed for surface treatment of zinc-based metal plated steel
sheets.
[0005] Chromate treatment has problems with inherent toxicity of
chromium compounds. In particular, hexavalent chromium compounds
are extremely harmful substances designated as human carcinogens by
IARC (International Agency for Research on Cancer Review) and many
other public organizations. Specifically stated, chromate treatment
has problems with chromate fumes produced during the treatment
process, extremely high cost required for waste water disposal
equipment, chromic acid dissolved out from chromate treatment
coats, and the like.
[0006] Phosphate treatment using zinc phosphate, iron phosphate or
like phosphate is usually followed by chromate post-treatment, and
thus involves the problems with toxicity of chromium compounds.
Moreover, phosphate treatment has problems with disposal of waster
water which contains reaction accelerators, metal ions and the like
owing to phosphate treatment agents, and sludge disposal
necessitated by metal ions dissolved out from treated metals.
[0007] Japanese Unexamined Patent Publications No. 1983-224174, No.
1985-50179 and No. 1985-50180 disclose coated steel sheets each
comprising a zinc-based metal plated steel sheet as a substrate, a
chromate coat formed on the substrate and an organic silicate coat
formed on the chromate coat. The disclosed coated steel sheets are
excellent in corrosion resistance and processability, but have the
problems with toxicity of chromium compounds owing to the chromate
coat. Without the chromate coat, the coated steel sheets have
insufficient corrosion resistance.
[0008] Aluminum or aluminum alloy substrates are also subjected to
various types of surface treatment (undercoating) in many cases, to
improve the corrosion resistance, hydrophilicity and other
properties.
[0009] Generally, fins in heat exchangers for air conditioners are
made of aluminum or aluminum alloy substrates which are light in
weight and excellent in processability and thermal conductivity. In
air conditioner heat exchangers, water condenses into droplets and
forms water bridges between the fins during cooling operation. The
bridges narrow the passageway for air and increase the resistance
to air passage, thus causing problems such as power loss, noise,
water splashing, etc.
[0010] To solve these problems, surfaces of the aluminum or
aluminum alloy fins are subjected to boehmite treatment, water
glass coating, aqueous polymer coating or like hydrophilizing
treatment for preventing bridge formation. However, in a highly
corrosive environment, the hydrophilized aluminum or aluminum alloy
fins are corroded within a few months or so, partly because of the
hydrophilicity of the treatment coat.
[0011] To prevent corrosion of the fins, chromate treatment is
often employed for undercoating of aluminum or aluminum alloy
substrates, since chromate treatment has the advantages of
providing good corrosion resistance with low cost. However,
chromate treatment is accompanied by the problems with toxicity of
chromium compounds as described above.
[0012] As chromate-free undercoating materials and undercoating
processes, Japanese Unexamined Patent Publication No. 1979-24232
discloses treatment of an aluminum surface with an acid solution
comprising a titanium salt, hydrogen peroxide and condensed
phosphoric acid; Japanese Unexamined Patent Publication No.
1979-160527 discloses treatment of an aluminum surface with an
aqueous alkaline solution containing titanium ions and a complexing
agent, followed by water washing and treatment with an aqueous
solution of an acid such as phosphoric acid; Japanese Unexamined
Patent Publication No. 1997-20984 discloses an aluminum surface
treating agent comprising phosphoric acid ions, a titanium compound
and a fluoride; and Japanese Unexamined Patent Publication No.
1997-143752 discloses an aluminum-based metal surface treating
agent comprising a condensed phosphate, titanium salt, fluoride and
phosphite.
[0013] However, these undercoating materials and processes
utilizing titanium compounds have the problems such as insufficient
stability of the undercoating materials, lower corrosion resistance
of the coat than a chromate treatment coat, insufficient
hydrophilicity and insufficient durability of the coat.
[0014] In view of the above state of the art, there are demands for
an inorganic film-forming material which is useful as an
undercoating material for metal substrates such as steel sheets,
aluminum, aluminum alloys or the like, and which is capable of
forming a film excellent in corrosion resistance and other
properties without causing toxicity problems.
DISCLOSURE OF THE INVENTION
[0015] An object of the present invention is to provide a novel
coating composition and process for forming, on a metal substrate,
a titanium oxide film, the composition and process being capable of
forming a film excellent in corrosion resistance, adhesion,
processability and like properties.
[0016] Another object of the invention is to provide a metal
substrate coated with a titanium oxide film excellent in corrosion
resistance, adhesion, processability and like properties.
[0017] Other objects and features of the present invention will
become apparent from the following description.
[0018] The present invention provides the following novel coating
compositions for forming titanium oxide films, processes for
forming titanium oxide films and metal substrates coated with
titanium oxide films:
[0019] 1. A coating composition for forming a titanium oxide film,
comprising (A) a titanium-containing aqueous liquid obtained by
mixing at least one titanium compound selected from the group
consisting of hydrolyzable titanium compounds., low condensates of
hydrolyzable titanium compounds, titanium hydroxide and low
condensates of titanium hydroxide with aqueous hydrogen peroxide,
and (B) at least one compound selected from the group consisting of
organic acids and their salts.
[0020] 2. A coating composition according to item 1, wherein the
titanium-containing aqueous liquid (A) is an aqueous peroxo titanic
acid solution obtained by mixing a hydrolyzable titanium compound
and/or its low condensate with aqueous hydrogen peroxide.
[0021] 3. A coating composition according to item 2, wherein the
hydrolyzable titanium compound is a tetraalkoxytitanium represented
by the formula
Ti(OR).sub.4 (1)
[0022] wherein Rs may be the same or different and each represent
C.sub.1 to C.sub.5 alkyl.
[0023] 4. A coating composition according to item 2, wherein the
low condensate of a hydrolyzable titanium compound is a compound
having a condensation degree of 2 to 30 and obtained by
self-condensation of tetraalkoxytitanium(s) represented by the
formula
Ti(OR).sub.4 (1)
[0024] wherein Rs may be the same or different and each represent
C.sub.1 to C.sub.5 alkyl.
[0025] 5. A coating composition according to item 2, wherein the
proportion of the aqueous hydrogen peroxide is 0.1 to 100 parts by
weight calculated as hydrogen peroxide, per 10 parts by weight of
the hydrolyzable titanium compound and/or its low condensate.
[0026] 6. A coating composition according to item 2, wherein the
titanium-containing aqueous liquid (A) is an aqueous peroxo titanic
acid solution obtained by mixing a hydrolyzable titanium compound
and/or its low condensate with aqueous hydrogen peroxide in the
presence of a titanium oxide sol.
[0027] 7. A coating composition according to item 6, wherein the
titanium oxide sol is an aqueous dispersion of anatase titanium
oxide.
[0028] 8. A coating composition according to item 6, wherein the
proportion of the titanium oxide sol is 0.01 to 10 parts by weight
as solids, per 1 part by weight of the hydrolyzable titanium
compound and/or its low condensate.
[0029] 9. A coating composition according to item 1, wherein the
compound (B) is at least one compound selected from the group
consisting of hydroxycarboxylic acids, hydroxyl-containing organic
phosphorous acids, carboxyl-containing organic phosphorous acids
and salts of these acids.
[0030] 10. A coating composition according to item 1, wherein the
proportion of the compound (B) is 1 to 400 parts by weight per 100
parts by weight of the solids in the titanium-containing aqueous
liquid (A).
[0031] 11. A coating composition according to item 1, which is an
aqueous liquid having a pH of 1 to 10.
[0032] 12. A coating composition according to item 11, which is an
aqueous liquid having a pH of 1 to 9.
[0033] 13. A coating composition according to item 1, which further
comprises an inorganic phosphoric acid compound.
[0034] 14. A coating composition according to item 1, which further
comprises at least one halide selected from the group consisting of
titanium halides, titanium halide salts, zirconium halides,
zirconium halide salts, silicon halides and silicon halide
salts.
[0035] 15. A coating composition according to item 1, which further
comprises an aqueous organic high molecular compound.
[0036] 16. A process for forming a titanium oxide film, comprising
applying a coating composition according to item 1 to a metal
substrate, followed by drying.
[0037] 17. A coated metal substrate comprising a metal substrate
and a film of a coating composition according to item 1 formed on a
surface of the substrate.
[0038] 18. A coated metal substrate according to item 17, wherein
the film has a dry weight of 0.001 to 10 g/m.sup.2.
[0039] 19. A coated metal substrate according to item 17, wherein
the metal substrate is made of steel.
[0040] 20. A coated metal substrate according to item 17, wherein
the metal substrate is made of aluminium or an aluminum alloy.
[0041] The present inventors carried out extensive research to
achieve the above objects. As a result, the inventors found that a
coating composition comprising the titanium-containing aqueous
liquid (A) and the compound (B), such as an organic acid, is
capable of forming, on a metal substrate, a film which is excellent
in corrosion resistance, adhesion, processability and like
properties, and which is suitable as an undercoat.
[0042] The present invention has been accomplished based on these
novel findings.
[0043] Coating Composition for Forming Titanium Oxide Film
[0044] The coating composition for forming a titanium oxide film of
the present invention is an aqueous coating composition comprising
the titanium-containing aqueous liquid (A) and the compound (B)
selected from organic acids and their salts.
[0045] The aqueous liquid component (A) for use in the coating
composition can be suitably selected from known titanium-containing
aqueous liquids obtainable by mixing at least one titanium compound
selected from the group consisting of hydrolyzable titanium
compounds, low condensates of hydrolyzable titanium compounds,
titanium hydroxide and low condensates of titanium hydroxide, with
aqueous hydrogen peroxide.
[0046] The hydrolyzable titanium compounds are titanium compounds
each containing a hydrolyzable group or groups bonded directly to a
titanium atom. The compounds produce titanium hydroxide when
reacted with water, water vapor or the like. In the hydrolyzable
titanium compounds, the groups bonded to the titanium atom may be
all hydrolyzable groups, or part of the groups may be previously
hydrolyzed to hydroxyl groups.
[0047] The hydrolyzable groups may be any groups capable of
producing hydroxyl groups when reacted with water. Examples of such
groups include lower alkoxyl, and groups forming salts with
titanium atoms. Examples of the groups forming salts with titanium
atoms include halogen atoms (e.g., chlorine atoms), hydrogen atoms,
sulfuric acid ions and the like.
[0048] Examples of hydrolyzable titanium compounds containing lower
alkoxyl groups as hydrolyzable groups include tetraalkoxytitaniums
and the like.
[0049] Typical examples of hydrolyzable titanium compounds
containing, as hydrolyzable groups, groups forming salts with
titanium include titanium chloride, titanium sulfate and the
like.
[0050] The low condensates of hydrolyzable titanium compounds are
products of low self-condensation of the hydrolyzable titanium
compounds. In the low condensates, the groups bonded to the
titanium atom may be all hydrolyzable groups, or part of the groups
may be previously hydrolyzed to hydroxyl groups.
[0051] Examples of low condensates of titanium hydroxide include
orthotitanic acid (titanium hydroxide gel) obtained by reaction of
an aqueous solution of titanium chloride, titanium sulfate or the
like with an aqueous solution of an alkali such as ammonia or
caustic soda.
[0052] The low condensates of hydrolyzable titanium compounds or
low condensates of titanium hydroxide have a condensation degree of
2 to 30, preferably 2 to 10.
[0053] The aqueous liquid (A) may be a known titanium-containing
aqueous liquid obtained by reaction of the above titanium compound
with aqueous hydrogen peroxide. Specific examples of such aqueous
liquids include the following:
[0054] (1) Aqueous peroxo titanic acid solutions described in
Japanese Unexamined Patent Publications No. 1988-35419 and No.
1989-224220, obtained by adding aqueous hydrogen peroxide to a gel
or sol of hydrous titanium oxide;
[0055] (2) Yellow, transparent, viscous aqueous liquids for forming
titanium oxide films, described in Japanese Unexamined Patent
Publications No. 1997-71418 and No. 1998-67516, obtained by:
reacting an aqueous solution of titanium chloride, titanium sulfate
or the like with an aqueous solution of an alkali such as ammonia
or caustic soda to precipitate a titanium hydroxide gel called
orthotitanic acid; isolating the titanium hydroxide gel by
decantation; washing the isolated gel with water; and adding
aqueous hydrogen peroxide to the gel;
[0056] (3) Titanium oxide film-forming aqueous liquids described in
Japanese Unexamined Patent Publications No. 2000-247638 and No.
2000-247639, obtained by: adding aqueous hydrogen peroxide to an
aqueous solution of an inorganic titanium compound such as titanium
chloride, titanium sulfate or the like to prepare a peroxo titanium
hydrate; adding a basic substance to the peroxo titanium hydrate;
allowing to stand or heating the resulting solution to precipitate
a peroxo titanium hydrate polymer; removing dissolved components
other than water; and allowing hydrogen peroxide to act.
[0057] Preferably, the titanium-containing aqueous liquid (A) is an
aqueous peroxo titanic acid solution (A1) obtained by mixing a
hydrolyzable titanium compound and/or its low condensate with
aqueous hydrogen peroxide.
[0058] A particularly preferred example of the titanium compounds
is a tetraalkoxytitanium represented by the formula
Ti(OR).sub.4 (1)
[0059] wherein Rs may be the same or different and each represent
C.sub.1 to C.sub.5 alkyl. Examples of C.sub.1 to C.sub.5 alkyl
represented by R include methyl, ethyl, n-propyl, isopropyl,
n-butyl, isobutyl, sec-butyl, tert-butyl and the like.
[0060] The low condensates of titanium compounds are preferably
self-condensates of the compounds of the formula (1), having a
condensation degree of 2 to 30, preferably 2 to 10.
[0061] The proportion of the aqueous hydrogen peroxide relative to
the hydrolyzable titanium compound of the formula (1) and/or its
low condensate (hereinafter the compound and/or its low condensate
is referred to simply as "hydrolyzable titanium compound (T)") is
preferably 0.1 to 100 parts by weight, particularly 1 to 20 parts
by weight, calculated as hydrogen peroxide, per 10 parts of
hydrolyzable titanium compound (T). Less than 0.1 part by weight of
aqueous hydrogen peroxide (calculated as hydrogen peroxide) results
in insufficient formation of peroxo titanic acid, producing opaque
precipitates. On the other hand, if more than 100 parts by weight
(calculated as hydrogen peroxide) of aqueous hydrogen peroxide is
used, it is likely that part of hydrogen peroxide remains unreacted
and emits hazardous active oxygen during storage.
[0062] The hydrogen peroxide concentration in the aqueous hydrogen
peroxide is not limited, but is preferably 3 to 40 wt. %,
considering ease of handling.
[0063] The aqueous peroxo titanic acid solution can be prepared
usually by mixing the hydrolyzable titanium compound (T) with
aqueous hydrogen peroxide with stirring at about 1 to 70.degree. C.
for about 10 minutes to about 20 hours. If necessary, methanol,
ethanol, n-propanol, isopropanol, ethylene glycol monobutyl ether,
propylene glycol monomethyl ether or like water-soluble solvent may
also be added.
[0064] Presumably, the aqueous peroxo titanic acid solution (A1) is
obtained through the following mechanism: When the hydrolyzable
titanium compound (T) is mixed with aqueous hydrogen peroxide, the
compound is hydrolyzed with water and formed into a
hydroxyl-containing titanium compound. Immediately thereafter,
hydrogen peroxide is coordinated to the hydroxyl-containing
titanium compound to thereby form peroxo titanic acid. The aqueous
peroxo titanic acid solution is highly stable at room temperature
and durable for long-term storage.
[0065] Also preferred is an aqueous peroxo titanic acid solution
(A2) obtained by mixing the hydrolyzable titanium compound (T) with
aqueous hydrogen peroxide in the presence of a titanium oxide sol,
since this solution has improved storage stability and is capable
of forming a titanium oxide film improved in corrosion resistance
and other properties. The reasons for the improvements is presumed
as follows: During preparation of the aqueous solution, the
hydrolyzable titanium compound (T) is adsorbed on the titanium
oxide sol particles and chemically bonded by condensation to
hydroxyl groups generated on the particle surface. Further, the
hydrolyzable titanium compound undergoes self-condensation and is
converted into a high molecular compound. The high molecular
compound is then mixed with aqueous hydrogen peroxide, thereby
giving a stable aqueous solution remarkably free of gelation or
thickening during storage.
[0066] The titanium oxide sol comprises amorphous titanium oxide
particles or anatase titanium oxide particles dispersed in water.
As the titanium oxide sol, an aqueous dispersion of anatase
titanium oxide is preferred from the viewpoint of corrosion
resistance. The titanium oxide sol may contain, in addition to
water, an aqueous organic solvent such as an alcohol solvent or an
alcohol ether solvent.
[0067] The titanium oxide sol may be a known one, such as a
dispersion of amorphous titanium oxide particles obtained by
dispersing titanium oxide agglomerates in water, or a dispersion in
water of anatase titanium oxide particles obtained by calcining
titanium oxide agglomerates. Amorphous titanium oxide can be
converted into anatase titanium oxide by calcination at a
temperature not lower than the anatase crystallization temperature,
usually at a temperature not lower than 200.degree. C. Examples of
titanium oxide agglomerates include (1) agglomerates obtained by
hydrolysis of an inorganic titanium compound such as titanium
sulfate or titanyl sulfate, (2) agglomerates obtained by hydrolysis
of an organic titanium compound such as titanium alkoxide, (3)
agglomerates obtained by hydrolysis or neutralization of a solution
of titanium halide such as titanium tetrachloride, and the
like.
[0068] Commercially available titanium oxide sols include, for
example, "TKS-201" (a tradename of TEICA Corp., an aqueous sol of
anatase titanium oxide particles with an average particle size of 6
nm), "TKS-203" (a tradename of TEICA Corp., an aqueous sol of
anatase titanium oxide particles with an average particle size of 6
nm), "TA-15" (a tradename of Nissan Chemical Industries, Ltd., an
aqueous sol of anatase titanium oxide particles) and "STS-11" (a
tradename of Ishihara Sangyo Kaisha, Ltd., an aqueous sol of
anatase titanium oxide particles).
[0069] The amount of the titanium oxide sol used when mixing the
hydrolyzable titanium compound (T) and aqueous hydrogen peroxide is
usually 0.01 to 10 parts by weight as solids, preferably 0.1 to 8
parts by weight as solids, per 1 part by weight of the hydrolyzable
titanium compound (T). Less than 0.01 part by weight of the
titanium oxide sol fails to achieve the effect of adding the
titanium oxide sol, i.e., improvement in storage stability of the
coating composition and in corrosion resistance of the titanium
oxide film. On the other hand, more than 10 parts by weight of the
sol impairs the film-forming properties of the coating composition.
Thus, an amount outside the above range is undesirable.
[0070] The titanium-containing aqueous liquid (A) may be used in
the form of a dispersion of titanium oxide particles with an
average particle size not greater than 10 nm. Such a dispersion can
be prepared by mixing the hydrolyzable titanium compound (T) with
aqueous hydrogen peroxide optionally in the presence of the
titanium oxide sol, and then subjecting the resulting aqueous
peroxo titanic acid solution to heat treatment or autoclave
treatment at a temperature not lower than 80.degree. C. The
dispersion usually has a translucent appearance.
[0071] If the heat treatment or autoclave treatment is carried out
at a temperature lower than 80.degree. C., the crystallization of
titanium oxide does not proceed sufficiently. The titanium oxide
particles obtained by heat treatment or autoclave treatment have a
particle size of not greater than 10 nm, preferably 1 nm to 6 nm.
If the titanium oxide particles have a particle size greater than
10 nm, the resulting coating composition has such a low
film-forming properties that a film with a dry weight of 1
g/m.sup.2 or greater develops cracks.
[0072] The aqueous solution (A1), when used as the
titanium-containing aqueous liquid (A), usually forms an amorphous
titanium oxide film containing a slight amount of hydroxyl groups,
under the above drying conditions. The amorphous titanium oxide
film has the advantage of higher gas barrier properties. When the
titanium-containing aqueous solution (A2) is used as the aqueous
solution (A), the solution usually forms an anatase titanium oxide
film containing a slight amount of hydroxyl groups, under the above
drying conditions.
[0073] In the coating composition of the present invention, the at
least one compound (B) selected from the group consisting of
organic acids and their salts act mainly to improve the corrosion
resistance of the resulting film and the storage stability of the
coating composition.
[0074] Examples of organic acids for use as the compound (B)
include organic carboxylic acids such as acetic acid, oxalic acid,
glycolic acid, lactic acid, malic acid, citric acid, tartaric acid
and gluconic acid; organic sulfonic acids such as methanesulfonic
acid, ethanesulfonic acid and p-benzenesulfonic acid; organic
sulfinic acids such as 2-amino-ethanesulfinic acid and
p-toluenesulfinic acid; organic nitro compounds such as
nitromethane, nitroethane, nitropropionic acid, nitrocatechol,
2-nitroresorcinol and nitrobenzoic acid; phenols such as phenol,
catechol, resorcinol, hydroquitione, pyrogallol, salicylic acid,
gallic acid, benzoic acid, thiophenol, 2-aminothiophenol and
4-ethylthiophenol; organic phosphoric acid compounds such as
1-hydroxymethane-1,1-diphosphonic acid,
1-hydroxyethane-1,1-diphosphonic acid,
1-hydroxypropane-1,1-diphosphonic acid,
nitrilo(amino)trimethylenep- hosphonic acid,
nitrilo(amino)triethylenephosphonic acid,
nitrilo(amino)tripropylenephosphonic acid, ethylenediamine
tetramethylenephosphonic acid, ethylenediamine
tetraethylenephosphonic acid, ethylenediamine
tetrapropylenephosphonic acid,
N,N-bis(2-phosphoethyl)-hydroxylamine,
N,N-bis(2-phosphomethyl)hydroxyami- ne, hydrolysates of
2-hydroxyethyl phosphonic acid dimethyl ether,
2-hydroxyphosphonoacetic acid and
2-phosphonobutane-1,2,4-tricarboxylic acid; and the like.
[0075] Salts of organic acids for use as the compound (B) may be
those formed by adding an alkali compound to any of the above
organic acids. Examples of the alkali compound include organic or
inorganic alkali compounds containing lithium, sodium, potassium,
ammonium or the like.
[0076] Preferably, the compound (B) is soluble in water.
[0077] It is particularly preferable to use, as the compound (B),
at least one compound selected from the group consisting of:
hydroxycarboxylic acids, such as glycolic acid, lactic acid, malic
acid, citric acid, tartaric acid and gluconic acid;
hydroxyl-containing organic phosphorous acids, such as
1-hydroxymethane-1,1-diphosphonic acid,
1-hydroxyethane-1,1-diphosphonic acid and
1-hydroxypropane-1,1-diphosphon- ic acid; carboxyl-containing
organic phosphorous acids such as
2-phosphonobutane-1,2,4-tricarboxylic acid,
2-hydroxyphosphonoacetic acid; and their salts, since these
compounds show excellent effects on the storage stability of the
coating composition, the corrosion resistance of the resulting
film, etc.
[0078] The proportion of the compound (B) relative to the
titanium-containing aqueous liquid (A) is preferably about 1 to 400
parts by weight, more preferably about 10 to 200 parts by weight,
per 100 parts by weight of the solids in the aqueous liquid (A).
Use of less than 1 part by weight of the compound (B) results in
lowered corrosion resistance, whereas more than 400 parts by weight
of the compound (B), if used, impairs the film-forming properties
and reduce the corrosion resistance. Therefore, a proportion
outside the specified range is undesirable.
[0079] The coating composition of the present invention is prepared
by mixing the titanium-containing aqueous liquid (A) and the at
least one compound (B) selected from the group consisting of
organic acids and their salts.
[0080] Presumably, in the coating composition of the present
invention, acidic ions of organic acid group(s) in the compound (B)
coordinate to titanium ions so that a complex structure is formed
between the acidic ions and the titanium ions. Examples of such
organic acid groups include hydroxyl, carboxyl, phosphorous acid
and like groups. The complex structure can be easily formed simply
by mixing the components (A) and (B), and then allowing the mixture
to stand, for example, at room temperature (20.degree. C.) for
about 5 minutes to about 1 hour. The mixture may be heated, for
example, at about 30 to 70.degree. C. for about 1 to 30 minutes to
form a complex structure.
[0081] The coating composition of the present invention is a stable
aqueous liquid, and usually has a pH of 1 to 10. The composition
has particularly good storage stability when it is in an acidic
region or weakly alkaline region, and has a pH of preferably 1 to
9, more preferably 1 to 7, further more preferably 1 to 5.
[0082] The coating composition may optionally contain, for example,
methanol, ethanol, isopropyl alcohol, ethylene glycol, propylene
glycol or like hydrophilic solvent. The coating composition may be
used as diluted with water or hydrophilic solvent, as required.
[0083] The coating composition may contain, as required, an
inorganic phosphoric acid compound to improve the corrosion
resistance of the resulting film.
[0084] Usable inorganic phosphoric acid compounds include, for
example, monophosphoric acids such as phosphorous acid, strong
phosphoric acid, triphosphoric acid, hypophosphorous acid,
hypophosphoric acid, trimetaphosphoric acid, diphosphorous acid,
diphosphoric acid, pyrophosphorous acid, pyrophosphoric acid,
metaphosphorous acid, metaphosphoric acid and orthophosphoric acid;
derivatives and salts of monophosphoric acids; condensed phosphoric
acids such as tripolyphosphoric acid, tetraphosphoric acid and
hexaphosphoric acid; derivatives and salts of condensed phosphoric
acids; and the like. These compounds can be used either singly or
in combination. Further, these phosphoric acid compounds may be in
the form of salts with alkali compounds. Examples of alkali
compounds include organic or inorganic alkali compounds containing
lithium, sodium, potassium, ammonium or the like.
[0085] These inorganic phosphoric acid compounds are preferably
soluble in water.
[0086] Particularly preferred phosphoric acid compounds are
orthophosphoric acid, sodium pyrophosphate, sodium
tripolyphosphate, sodium tetraphosphate, metaphosphoric acid,
ammonium metaphosphate, sodium hexametaphosphate and the like,
since these phosphoric acid compounds remarkably improve the
storage stability of the coating composition, the corrosion
resistance of the resulting film, etc.
[0087] When an inorganic phosphoric acid compound is used, the
proportion of the phosphoric acid compound relative to the
titanium-containing aqueous liquid (A) is preferably about 1 to 400
parts by weight, more preferably 10 to 200 parts by weight, per 100
parts by weight of the solids in the aqueous liquid (A).
[0088] The coating composition of the present invention may
contain, as required, at least one halide selected from the group
consisting of titanium halides, titanium halide salts, zirconium
halides, zirconium halide salts, silicon halides and silicon halide
salts, to further improve the corrosion resistance of the resulting
film.
[0089] Examples of halogens in these halides include fluorine,
chlorine, iodine and the like. Among them, fluorine is particularly
preferred to achieve excellent storage stability of the coating
composition, high corrosion resistance and moisture resistance of
the film, etc. The halide salts are, for example, salts formed with
sodium, potassium, lithium, ammonium or the like. Among them,
potassium, sodium and ammonium are preferred.
[0090] Preferred examples of halides include titanium hydrofluoric
acid and like titanium halides; potassium titanium fluoride,
ammonium titanium fluoride and like titanium halide salts;
zirconium hydrofluoric acid and like zirconium halides; ammonium
zirconium fluoride, potassium zirconium fluoride and like zirconium
halide salts; hydrosilicofluoric acid and like silicon halides;
sodium silicofluoride, ammonium silicofluoride, potassium
silicofluoride and like silicon halide salts; and the like.
[0091] When any of the above halides is used in the coating
composition of the present invention, the proportion thereof is
preferably about 1 to 400 parts by weight, more preferably about 10
to 200 parts by weight, per 100 parts by weight of the solids in
the titanium-containing aqueous liquid (A).
[0092] The coating composition of the present invention may
contain, as required, an aqueous organic high molecular compound to
improve the film-forming properties of the coating composition, the
adhesion to the topcoat, etc.
[0093] The aqueous organic high molecular compound may be in the
form of an aqueous solution, an aqueous dispersion or an emulsion.
The compound can be solubilized, dispersed or emulsified in water
by known methods.
[0094] Examples of the aqueous organic high molecular compound
include compounds having functional groups (e.g., at least one of
hydroxyl, carboxyl, amino, imino, sulfide, phosphine and the like)
which are by themselves capable of solubilizing or dispersing the
compounds in water, and such compounds in which part or all of the
functional groups have been neutralized. When the compound is an
acidic resin such as a carboxyl-containing resin, the compound can
be neutralized with ethanolamine, triethylamine or like amine
compound; aqueous ammonia; lithium hydroxide, sodium hydroxide,
potassium hydroxide or like alkali metal hydroxide; or the like.
When the compound is a basic resin such as an amino-containing
resin, the compound can be neutralized with acetic acid, lactic
acid or like fatty acid; phosphoric acid or like mineral acid; or
the like.
[0095] Examples of the aqueous organic high molecular compound
include epoxy resins, phenol resins, acrylic resins, urethane
resins, polyvinyl alcohol resins, polyoxyalkylene chain-containing
resins, olefin-polymerizable unsaturated carboxylic acid copolymer
resins, nylon resins, polyglycerin, carboxymethyl cellulose,
hydroxymethyl cellulose, hydroxyethyl cellulose and the like.
[0096] Preferably, the compound is an epoxy resin, a phenol resin,
an acrylic resin, a urethane resin, a polyvinyl alcohol resin, a
polyoxyalkylene chain-containing resin, an olefin-polymerizable
unsaturated carboxylic acid copolymer resin or the like.
[0097] When the compound is highly hydrophilic, the resulting
composition is capable of forming a film having both high corrosion
resistance and high hydrophilicity, and thus is suitable as a
hydrophilizing agent for fins made of aluminum or aluminum
alloy.
[0098] Preferred examples of epoxy resins include cationic epoxy
resins obtained by addition of amine to epoxy resins; acrylic
modified epoxy resins, urethane modified epoxy resins and like
modified epoxy resins; and the like. Examples of cationic epoxy
resins include adducts of epoxy compounds with primary mono- or
polyamines, secondary mono- or polyamines, mixtures of primary and
secondary polyamines (see, for example, U.S. Pat. No. 3,984,299);
adducts of epoxy compounds with secondary mono- or polyamines
having ketiminized primary amino groups (see, for example, U.S.
Pat. No. 4,017,438); etherification reaction products of epoxy
compounds with hydroxyl compounds having ketiminized primary amino
groups (see, for example, Japanese Unexamined Patent Publication
No. 1984-43013); and the like.
[0099] Preferred epoxy compounds include those having a number
average molecular weight of 400 to 4,000, particularly 800 to
2,000, and an epoxy equivalent of 190 to 2,000, particularly, 400
to 1,000. Such epoxy compounds can be obtained by, for example,
reaction of polyphenol compounds with epichlorohydrin. Examples of
polyphenol compounds include bis(4-hydroxyphenyl)-2,2-propane,
4,4-dihydroxybenzophenone, bis(4-hydroxyphenyl)-1,1-ethane,
bis(4-hydroxyphenyl)-1,1-isobutane,
bis(4-hydroxy-tert-butylphenyl)-2,2-propane,
bis(2-hydroxynaphthyl)methan- e, 1,5-dihydroxynaphthalene,
bis(2,4-dihydroxyphenyl)methane,
tetra(4-hydroxyphenyl)-1,1,2,2-ethane,
4,4-dihydroxydiphenylsulfone, phenol novolac, cresol novolac and
the like.
[0100] Preferred phenol resins include those prepared by
water-solubilizing high. molecular compounds obtained by addition
and condensation of phenol components and formaldehydes by heating
in the presence of reaction catalysts. Usable as the starting
phenol components are bifunctional phenol compounds, trifunctional
phenol compounds, tetra- or higher functional phenol compounds or
the like. Examples of bifunctional phenol compounds include
o-cresol, p-cresol, p-tert-butylphenol, p-ethyl phenol,
2,3-xylenol, 2,5-xylenol and the like. Examples of trifunctional
phenol compounds include phenol, m-cresol, m-ethylphenol,
3,5-xylenol, m-methoxyphenol and the like. Examples of
tetrafunctional phenol compounds include bisphenol A, bisphenol F
and the like. These phenol compounds may be used either singly or
in combination.
[0101] Preferred acrylic resins include, for example, homopolymers
or copolymers of monomers having hydrophilic groups such as
carboxyl, amino or hydroxyl, copolymers of hydrophilic
group-containing monomers with other copolymerizable monomers, and
the like. These resins are obtained by emulsification
polymerization, suspension polymerization or solution
polymerization, optionally followed by neutralization for
conversion to aqueous resins. The resulting resins may be further
modified, if required.
[0102] Examples of carboxyl-containing monomers include acrylic
acid, methacrylic acid, maleic acid, maleic anhydride, crotonic
acid, itaconic acid and the like.
[0103] Examples of nitrogen-containing monomers include
N,N-dimethylaminoethyl(meth)acrylate,
N,N-diethylaminoethyl(meth)acrylate- ,
N-t-butylaminoethyl(meth)acrylate and like nitrogen-containing
alkyl(meth)acrylates; acrylamide, methacrylamide,
N-methyl(meth)acrylamid- e, N-ethyl(meth)acrylamide,
N-methylol(meth)acrylamide, N-methoxymethyl(meth)acrylamide,
N-butoxymethyl(meth)acrylamide, N,N-dimethyl(meth)acrylamide,
N,N-dimethylaminopropyl(meth)acrylamide,
N,N-dimethylaminoethyl(meth)acrylamide and like polymerizable
amides; 2-vinylpyridine, 1-vinyl-2-pyrolidone, 4-vinylpyridine and
like aromatic nitrogen-containing monomers; allyl amines; and the
like.
[0104] Examples of hydroxyl-containing monomers include
2-hydroxyethyl(meth)acrylate, hydroxypropyl (meth)acrylate,
2,3-dihydroxybutyl(meth)acrylate, 4-hydroxybutyl(meth)acrylate,
polyethylene glycol mono(meth)acrylate and like monoesters of
polyhydric alcohols with acrylic acid or methacrylic acid;
compounds obtained by subjecting the monoesters of polyhydric
alcohols and acrylic acid or methacrylic acid to ring-opening
polymerization with .epsilon.-caprolactone; and the like.
[0105] Other polymerizable monomers include, for example,
methyl(meth)acrylate, ethyl(meth)acrylate, n-propyl(meth)acrylate,
isopropyl(meth)acrylate, n-butyl(meth)acrylate,
isobutyl(meth)acrylate, tert-butyl(meth)acrylate,
2-ethylhexyl(meth)acrylate, n-octyl(meth)acrylate,
lauryl(meth)acrylate, tridecyl(meth)acrylate,
octadecyl(meth)acrylate, isostearyl(meth)acrylate and like C.sub.1
to C.sub.24 alkyl(meth)acrylates; styrene; vinyl acetate; and the
like. These compounds may be used either singly or in
combination.
[0106] As used herein, the term "(meth)acrylate" is intended to
mean acrylate or methacrylate.
[0107] Preferred urethane resins include those prepared by:
subjecting polyurethane resins obtained from polyols (e.g.,
polyester polyols or polyether polyols) and diisocyanate to chain
extension optionally in the presence of, as a chain extender, a low
molecular compound having at least two active hydrogen atoms, such
as diol or diamine; and then dispersing or dissolving the urethane
resins stably in water. Such urethane resins are disclosed in, for
example, Japanese Examined Patent Publications No. 1967-24192, No.
1967-24194, No. 1967-5118, No. 1974-986, No. 1974-33104, No.
1975-15027 and No. 1978-29175.
[0108] The polyurethane resins can be dispersed or dissolved stably
in water, for example, by the following methods:
[0109] (1) Introduce an ionic group such as hydroxyl, amino or
carboxyl into the side chain or the terminal of a polyurethane
resin to impart hydrophilicity to the resin; and disperse or
dissolve the resin in. water by self-emulsification.
[0110] (2) Disperse a polyurethane resin that has completed
reaction or a polyurethane resin whose terminal isocyanate group is
blocked with a blocking agent, forcibly in water using an
emulsifier and mechanical shear force. Examples of usable blocking
agents include oximes, alcohols, phenols, mercaptans, amines and
sodium bisulfite.
[0111] (3) Mix an isocyanate-terminated polyurethane resin, water,
an emulsifier and a chain extender; and using mechanical shear
force, disperse the resin while converting the resin into a high
molecular resin.
[0112] (4) Disperse or dissolve in water a polyurethane resin
prepared using, as a starting polyol, a water-soluble polyol such
as polyethylene glycol.
[0113] The aqueous resins prepared by dispersing or dissolving
polyurethane resins by the above methods can be used either singly
or in combination.
[0114] Diisocyanates usable for synthesis of the polyurethane
resins include aromatic, alicyclic or aliphatic diisocyanates.
Specific examples of these diisocyanates include hexamethylene
diisocyanate, tetramethylene diisocyanate,
3,3'-dimethoxy-4,4'-biphenylene diisocyanate, p-xylylene
diisocyanate, m-xylylene diisocyanate,
1,3-(diisocyanatomethyl)-cyclohexa- none,
1,4-(diisocyanatomethyl)cyclohexanone,
4,4'-diisocyanatocyclohexanon- e, 4,4'-methylenebis(cyclohexyl
isocyanate), isophorone diisocyanate, 2,4-tolylene diisocyanate,
2,6-tolylene diisocyanate, p-phenylene diisocyanate,
diphenylmethane diisocyanate, m-phenylene diisocyanate,
2,4-naphthalene diisocyanate, 3,3'-dimethyl-4,4'-biphenylene
diisocyanate, 4,4'-biphenylene diisocyanate, and the like. Among
them, particularly preferred are 2,4-tolylehe diisocyanate,
2,6-tolylene diisocyanate, hexamethylene diisocyanate and
isophorone diisocyanate.
[0115] Commercial products of the polyurethane resins include, for
example, "Hydran HW-330", "Hydran HW-340" and "Hydran HW-350"
(tradenames of Dainippon Ink and Chemicals, Inc.), "Superflex 100",
"Superflex 150" and "Superflex F-3438D" (tradehames of Dai-ichi
Kogyo Seiyaku Co., Ltd.), and the like.
[0116] Preferred polyvinyl. alcohol resins are those having a
saponification degree not lower than 87%, in particular so-called
completely saponified polyvinyl alcohols having a saponification
degree not lower than 98%. Further, the resins preferably have a
number average molecular weight of 3,000 to 100,000.
[0117] Usable polyoxyalkylene chain-containing resins include
resins containing polyoxyethylene chains or polyoxypropylene
chains. Examples of such resins include polyethylene glycol,
polypropylene glycol, blocked polyoxyalkylene glycol in which
polyoxyethylene chains and polyoxypropylene chains are bonded to
form blocks, and the like.
[0118] Preferred as the olefin-polymerizable unsaturated carboxylic
acid copolymer resin is at least one of two types of
water-dispersible or water-soluble resins, i.e., (i) a copolymer of
ethylene, propylene or like olefin and (meth)acrylic acid, maleic
acid or like polymerizable unsaturated carboxylic acid, and (ii) a
crosslinked resin obtained by adding a polymerizable unsaturated
compound to an aqueous dispersion of the above copolymer for
emulsification polymerization followed by intraparticle
crosslinking.
[0119] The copolymer (i) comprises at least one olefin and at least
one polymerizable unsaturated carboxylic acid. It is preferable
that the copolymer comprises, as a monomer component, 3 to 60 wt.
%, preferably 5 to 40 wt. %, of unsaturated carboxylic acid or
acids. The copolymer can be dispersed in water by neutralizing acid
groups in the copolymer with a basic substance.
[0120] The polymerizable unsaturated compound to be added to an
aqueous dispersion of the above copolymer for emulsification
polymerization and intraparticle crosslinking to prepare the
crosslinked resin (ii) may be, for example, any of the vinyl
monomers listed above in the description of the water-dispersible
or water-soluble acrylic resins. These vinyl monomers can be used
either singly or in combination.
[0121] When using an aqueous organic high molecular compound in the
composition of the present invention, it is preferable that the
proportion of the aqueous organic high molecular compound be 10 to
2,000 parts by weight, particularly 100 to 1,000 parts by weight,
per 100 parts by weight of the solids in the titanium-containing
aqueous liquid (A), from the viewpoints of the stability of the
coating composition and the corrosion resistance of the resulting
titanium oxide film.
[0122] The coating composition of the present invention may
contain, as required, bivalent or higher valent ions of Al, Ca, Ti,
V, Mn, Co, Fe, Cu, Zn, Zr, Nb, Mo, Ta, W or the like, to improve
the acid resistance and alkali resistance of the resulting
film.
[0123] The coating composition of the present invention may further
contain, if necessary, ammonia, a basic organic compound, an alkali
metal hydroxide, an alkaline earth metal hydroxide or like basic
neutralizer. Preferred basic organic compounds include, for
example, ethanolamine and triethylamine, and preferred alkali metal
hydroxides include, for example, lithium hydroxide, sodium
hydroxide, potassium hydroxide and the like.
[0124] The coating composition may contain, if necessary, additives
such as a thickening agent, antimicrobial agent, rust-preventive
agent, titanium oxide sol, titanium oxide powder, extender pigment,
rust-preventive pigment, coloring pigment, surfactant or the like.
Usable rust-preventive agents include, for example, tannic acid,
phytic acid, benzotriazole, ammonium metavanadate, zirconium
ammonium carbonate and the like. Useful extender pigments include,
for example, mica, talc, silica, fine silica powder, baryta, clay
and the like. Addition of an extender pigment is advantageous since
it improves, when an upper coat is formed, the adhesion to the
upper coat by the anchor effects.
[0125] Process for Forming Titanium Oxide Film and Metal Substrate
Coated with Titanium Oxide Film
[0126] The process for forming a titanium oxide film according to
the present invention comprises applying the coating composition of
the present invention to a metal substrate, followed by drying. The
process produces a metal substrate coated with a titanium oxide
film. The coated metal substrate can be used by itself as a
rust-resistant coated metal substrate.
[0127] The metal substrate for use in the process of the present
invention may be any substrate at least having a metal surface.
Examples of usable substrates include those having a surface made
of iron, aluminum, magnesium, zinc, copper, tin or an alloy
containing any of these metals. Particularly preferred are steel
sheet substrates and aluminum or aluminum alloy substrates.
[0128] Examples of steel sheet substrates include hot-dip
galvanized steel sheets, electrogalvanized steel sheets, iron-zinc
alloy plated steel sheets, nickel-zinc alloy plated steel sheets,
aluminum-zinc alloy plated steel sheets and the like. Examples of
aluminium-zinc alloy plated steel sheets include those marketed
under tradenames "Galvalium" or "Galfan". Also usable as steel
sheet substrates are zinc-based metal plated steel sheets that have
been subjected to chemical conversion treatment such as chromate
treatment, zinc phosphate treatment or composite oxide film
treatment. Further, a steel sheet assembly can be employed as a
steel sheet substrate.
[0129] Typical examples of aluminium or aluminium alloy substrates
include, but are not limited to, heat exchanger fins. The heat
exchanger fin to be used as the substrate may be a known one, which
may be a separate member before assembly into a heat exchanger, or
a member assembled into a heat exchanger.
[0130] The coating composition of the present invention can be
applied to a metal substrate by any known process, such as dip
coating, shower coating, spray coating, roll coating and
electrocoating. It is usually preferable that the composition be
dried for about 2 seconds to about 30 minutes by heating under such
conditions that the substrate reaches a maximum temperature of
about 60 to 250.degree. C.
[0131] The amount of the coating composition to be applied is
preferably about 0.001 to 10 g/m.sup.2, more preferably 0.1 to 5
g/m.sup.2, based on a dry film weight. If the amount is less than
0.001 g/m.sup.2, the resulting film is poor in corrosion
resistance, water resistance or like properties, whereas if the
amount is more than 10 g/m.sup.2, the resulting film develops
cracks or has reduced corrosion resistance. Thus, an amount outside
the specified range is undesirable.
[0132] In this manner, the process of the present invention
produces, on a metal substrate, a titanium oxide film excellent in
corrosion resistance, adhesion, processability, fingerprint
resistance, etc.
[0133] The coating composition may be applied to a non-metal
substrate and dried to form a titanium oxide film.
[0134] Examples of non-metal substrates include, but are not
limited to, plastic substrates made of polyvinyl chloride resins,
polyethylene terephthalate, acrylic resins, silicon resins,
polyester resins, fluorine resins, epoxy resins, polyethylene
resins, nylon resins, butyral resins, cellulose resins, phenol
resins or combinations of two or more of these resins; glass,
cement or like inorganic substrates; wood, paper, fiber or like
pulp substrates; these plastic substrates, inorganic substrates or
pulp substrates as surface-treated or treated with primers; and the
like.
[0135] The coating composition can be applied to these substrates
by any known process, such as dip coating, shower coating, spray
coating, roll coating or electrocoating. It is usually preferable
that the composition be dried for about 2 seconds to about 30
minutes by heating under such conditions that the substrate reaches
a maximum temperature of about 20 to 250.degree. C. The amount of
the coating composition to be applied is preferably about 0.001 to
10 g/m.sup.2 based on a dry film weight.
[0136] An upper coat may be formed on the substrate coated with the
titanium oxide film of the coating composition of the present
invention. The composition for forming the upper coat can be
selected from various coating compositions according to the
intended purpose. Examples of coating compositions useful for
forming the upper coat include lubricant film-forming compositions,
highly corrosion resistant film-forming compositions, primer
compositions, colored topcoat compositions and the like. It is also
possible to apply and dry a lubricant film-forming composition, a
highly corrosion resistant film-forming composition or a primer
composition, and then further apply a colored topcoat composition
on the resulting. coat.
[0137] Aluminum or aluminum alloy substrates coated with the
coating composition of the present invention are excellent in
corrosion resistance, hydrophilicity, adhesion, processability and
like properties. The substrates, when irradiated with light, are
further improved in hydrophilicity.
[0138] When an aluminium or aluminium alloy substrate coated with a
film formed from the coating composition of the invention is used
for a heat exchanger fin, the film may be coated with a
hydrophilizing coat, if required.
[0139] The hydrophilizing coat has a hydrophilic surface,
sufficient strength, high water resistance and good adhesion to
undercoats. The hydrophilizing coat can be preferably formed by
applying and drying a hydrophilizing composition.
[0140] The hydrophilizing composition preferably contains a
hydrophilic film-forming binder. Preferred hydrophilic film-forming
binders include, for example, (1) an organic resin binder mainly
comprising a hydrophilic organic resin and optionally containing a
crosslinking agent, (2) an organic resin/colloidal silica binder
mainly comprising a hydrophilic organic resin and colloidal silica
and optionally containing a crosslinking agent, (3) a water glass
binder made of a mixture of alkali silicate and an anionic or
nonionic aqueous organic resin as main components, and the like.
Among these binders, the organic resin binder (1) and the organic
resin/colloidal silica binder (2) are particularly preferred.
BEST MODE FOR CARRYING OUT THE INVENTION
[0141] The following Production Examples, Examples and Comparative
Examples are provided to illustrate the present invention in
further detail, and do not limit the scope of the invention. In the
following examples, parts and percentages are all by weight.
[0142] Preparation of Titanium-Containing Aqueous Liquid (A)
PRODUCATION EXAMPLE 1
[0143] A 10% aqueous ammonia solution was added dropwise to 500 cc
of an aqueous solution obtained by diluting 5 cc of a 60% aqueous
titanium tetrachloride solution with distilled water, to
precipitate titanium hydroxide. The precipitates were washed with
distilled water, mixed with 10 cc of 30% aqueous hydrogen peroxide
and stirred, giving 70 cc of a yellow, translucent, viscous liquid
containing peroxo titanic acid (titanium-containing aqueous liquid
(1)) having a solid content of 2%.
PRODUCTION EXAMPLE 2
[0144] A mixture of 10 parts of tetraisopropoxy titanium and 10
parts of isopropanol was added dropwise to a mixture of 10 parts of
30% aqueous hydrogen peroxide and 100 parts of deionized water, at
20.degree. C. over 1 hour with stirring. Thereafter, the resulting
mixture was aged at 25.degree. C. for 2 hours, giving a yellow,
transparent, slightly viscous aqueous peroxo titanic acid solution
(titanium-containing aqueous liquid (2)) having a solid content of
2%.
PRODUCTION EXAMPLE 3
[0145] The procedure of Production Example 2 was repeated except
that 10 parts of tetra-n-butoxy titanium was used in place of
tetraisopropoxy titanium, giving titanium-containing aqueous liquid
(3) having a solid content of 2%.
PRODUCTION EXAMPLE 4
[0146] The procedure of Production Example 2 was repeated except
that 10 parts of a trimer of tetraisopropoxy titanium was used in
place of tetraisopropoxy titanium, giving titanium-containing
aqueous liquid (4) having a solid content of 2%.
PRODUCTION EXAMPLE 5
[0147] The procedure of Production Example 2 was repeated except
that a 3 times greater amount of aqueous hydrogen peroxide was
used, and that the dropwise addition was carried out at 50.degree.
C. over 1 hour, and that the subsequent aging was carried out at
60.degree. C. for 3 hours. In this manner, titanium-containing
aqueous liquid (5) having a solid content of 2% was obtained.
PRODUCTION EXAMPLE 6
[0148] The titanium-containing aqueous liquid obtained in
Production Example 3 was heated at 95.degree. C. for 6 hours,
giving a whitish yellow, translucent dispersion of titanium oxide
(titanium-containing aqueous liquid (6)) having a solid content of
2%.
PRODUCTION EXAMPLE 7
[0149] A mixture of 10 parts of tetraisopropoxy titanium and 10
parts of isopropanol was added dropwise to a mixture of 5 parts (as
solids) of "TKS-203" (a tradename of TEICA Corp., an aqueous sol of
anatase titanium oxide particles with an average particle size of 6
nm), 10 parts of 30% aqueous hydrogen peroxide and 100 parts of
deionized water, at 10.degree. C. over 1 hour with stirring.
Thereafter, the resulting mixture was aged at 10.degree. C. for 24
hours, giving yellow, transparent, slightly viscous
titanium-containing aqueous liquid (7) having a solid content of
2%.
[0150] Preparation of Aqueous Organic High Molecular Compounds
PRODUCTION EXAMPLE 8
[0151] A 1-liter, four-necked flask equipped with a thermometer,
stirrer, condenser and dropping funnel was charged with 180 parts
of isopropyl alcohol, and purged with nitrogen. Then, the
temperature inside the flask was adjusted to 85.degree. C. Added
dropwise over about 2 hours were a monomer mixture of 140 parts of
ethyl acrylate, 68 parts of methyl methacrylate, 15 parts of
styrene, 15 parts of N-n-butoxymethyl acrylamide, 38 parts of
2-hydroxyethyl acrylate and 24 parts of acrylic acid, and 6 parts
of 2,2'-azobis(2,4-dimethylvaleronitrile) as a catalyst. After
completion of the addition, the reaction was continued at the same
temperature for a further 5 hours. As a result, a colorless
transparent resin solution was obtained which had a polymerization
degree of nearly 100%, a solid content of about 63% and an acid
value of about 67 mgKOH/g. The resin solution (500 parts) was mixed
with 108 parts of dimethylamino ethanol. After addition of water,
the mixture was thoroughly stirred to obtain aqueous acrylic resin
dispersion (C1) having a solid content of 30%.
PRODUCTION EXAMPLE 9
[0152] A reactor equipped with a stirrer, reflux condenser,
thermometer and liquid dropper was charged with 1,880 g (0.5 moles)
of "Epikote 100938 (a tradename of Shell Chemical Co., an epoxy
resin having a molecular weight of 3,750) and 1,000 g of a mixed
solvent (methyl isobutyl ketone/xylene=1/1 in weight ratio). The
mixture in the reactor was then heated with stirring to obtain a
homogeneous solution. The solution was cooled to 70.degree. C., and
70 g of di(n-propanol)amine weighed into the liquid dropper was
added dropwise over 30 minutes. During the addition, the reaction
temperature was maintained at 70.degree. C. After completion of the
addition, the reaction mixture was maintained at 120.degree. C. for
2 hours to complete the reaction, giving an amine-modified epoxy
resin having a solid content of 66%. Twenty five parts of 88%
formic acid was added per 1,000 g of the resin. After addition of
water, the mixture was thoroughly stirred to obtain aqueous
amine-modified epoxy resin dispersion (C2) having a solid content
of 30%.
EXAMPLES OF COATING COMPOSITIONS OF THE PRESENT INVENTION
EXAMPLE 1
[0153] A coating composition for forming a titanium oxide film
according to the present invention was prepared by mixing 50 parts
of titanium-containing aqueous liquid (1) obtained in Production
Example 1, 2 parts of 60% 1-hydroxyethane-1,1-diphosphonic acid and
48 parts of deionized water.
EXAMPLES 2 TO 19 AND COMPARATIVE EXAMPLES 1 TO 2
[0154] Using the components shown in Table 1, coating compositions
of the present invention and comparative coating compositions were
prepared in the same manner as in Example 1.
1 TABLE 1 Example 1 2 3 4 5 6 7 8 9 10 11 Component (A) (1) 50 (2)
50 50 50 50 50 (3) 50 (4) 50 (5) 50 (6) 50 (7) 50 Component (B) 60%
1- 2 2 2 2 2 2 2 2 hydroxyethane- 1,1-diphosphonic acid 10%
glycolic 5 acid 10% malic acid 5 3 10% citric acid 5 10%
orthophosphoric acid 10% metaphosphoric acid 40% titanium
hydrofluoric acid 30% aqueous acrylic resin dispersion (C1) 30%
aqueous amine- modified epoxy resin dispersion (C2) 50% vinylidene
chloride resin(*1) 10% polyvinyl alcohol(*2) Fine silica powder(*3)
Deionized water 48 48 48 48 48 48 48 45 45 45 45 Comp. Example Ex.
12 13 14 15 16 17 18 19 1 2 Component (A) (1) 50 (2) 50 50 50 50 50
50 50 50 50 (3) (4) (5) (6) (7) Component (B) 60% 1- 2 2 2 2 2 2 2
2 hydroxyethane- 1,1-diphosphonic acid 10% glycolic acid 10% malic
acid 10% citric acid 10% orthophosphoric 5 acid 10% metaphosphoric
5 5 acid 40% titanium 1 hydrofluoric acid 30% aqueous acrylic 2
resin dispersion (C1) 30% aqueous amine- 1 modified epoxy resin
dispersion (C2) 50% vinylidene 1 chloride resin(*1) 10% polyvinyl
alcohol(*2) 3 Fine silica powder(*3) 1 Deionized water 43 43 47 42
46 47 47 45 50 50 In Table 1, *1 to *3 indicate the following: *1:
"Saran Latex L-411", a tradename of Asahi Kasei Corp., a vinylidene
chloride resin having a solid content of 50% *2: "Kuraray RS
Polymer RS-105", a tradename of Kuraray Co., Ltd., a polyvinyl
alcohol having a solid content of 10% *3: "Aerosil 380", a
tradename of Nippon Aerosil Co., Ltd., an extender pigment, a fine
silica powder having a specific surface area of 380 m.sup.2/g and
an average. particle size of 7 nm
PERFORMANCE TEST OF THE COATING COMPOSITIONS OF THE PRESENT
INVENTION
[0155] The coating compositions obtained in Examples 1 to 19 and
Comparative Examples 1 and 2 were applied to metal substrates. The
resulting coated substrates were tested for corrosion
resistance.
[0156] (1) Coating of Aluminum Sheets
[0157] Aluminum sheets (A1050) with a thickness of 0.1 mm were
degreased with a 2% aqueous solution of an alkaline degreasing
agent (a product of Japan CB Chemical Co., tradename "Chemicleaner
561B") and washed with water. The coating compositions were applied
by roller coating so that the dry film weight would be 0.2
g/m.sup.2, and baked for 20 seconds under such conditions that the
substrate temperature became 100.degree. C., to form titanium oxide
films.
[0158] (2) Corrosion Resistance of the Coated Sheets
[0159] The coated sheets were subjected to the salt spray test
defined in JIS Z2371 for 120, 240, 360 and 480 hours, and rated on
the following scale.
[0160] a: No white rusting or blistering on the coated surface;
[0161] b: Slight white rusting or blistering;
[0162] c: Serious white rusting or blistering.
[0163] Table 2 shows the test results.
2 TABLE 2 Coating Test period composition 120 hr 240 hr 360 hr 480
hr Ex. 1 a a a b Ex. 2 a a a b Ex. 3 a a a b Ex. 4 a a a b Ex. 5 a
a a b Ex. 6 a a b c Ex. 7 a a b c Ex. 8 a a b c Ex. 9 a a b c Ex.
10 a a b c Ex. 11 a a a b Ex. 12 a a a b Ex. 13 a a a a Ex. 14 a a
a a Ex. 15 a a a a Ex. 16 a a b c Ex. 17 a a b c Ex. 18 a a b c Ex.
19 a a b c Comp. Ex. 1 b c c c Comp. Ex. 2 b b c c
[0164] (3) Coating of Steel Sheets
[0165] Electrogalvanized steel sheets with a thickness of 0.6 mm
(the amount of plating on one side: 20 g/m.sup.2) were degreased
with a 2% aqueous solution of an alkaline degreasing agent (a
product of Japan CB Chemical Co., tradename "Chemicleaner 561B")
and washed with water. The coating compositions were applied by
roller coating so that the dry film weight would be 1.0 g/m.sup.2,
and baked for 20 seconds under such conditions that the substrate
temperature became 100.degree. C., to form titanium oxide
films.
[0166] (4) Corrosion Resistance of the Coated Sheets
[0167] The end faces and back face of the coated sheets were
sealed. The resulting sheets were subjected to the salt spray test
defined in JIS Z2371 for 24, 48 and 72 hours, and rated on the
following scale.
[0168] a: No white rusting;
[0169] b: Less than 5% of the coated surface area had white
rust;
[0170] c: Not less than 5% but less than 10% of the coated surface
area had white rust;
[0171] d: Not less than 10% but less than 50% of the coated surface
area had white rust;
[0172] e: 50% or more of the coated surface area had white
rust.
[0173] Table 3 shows the test results.
3 TABLE 3 Coating Test period composition 24 hr 48 hr 72 hr Ex. 1 a
a b Ex. 2 a a b Ex. 3 a a b Ex. 4 a a b Ex. 5 a a b Ex. 6 a b c Ex.
7 a b c Ex. 8 a b c Ex. 9 a b c Ex. 10 a b c Ex. 11 a a b Ex. 12 a
a a Ex. 13 a a a Ex. 14 a a a Ex. 15 a a a Ex. 16 a b c Ex. 17 a b
c Ex. 18 a b c Ex. 19 a b c Comp. Ex. 1 c d d Comp. Ex. 2 c c d
[0174] (5) Coating of Steel Sheets
[0175] The surfaces of electrogalvanized steel sheets with a
thickness of 0.6 mm (the amount of plating on one side: 20
g/m.sup.2) were alkaline degreased and conditioned by spray coating
with "Preparen Z" (a tradename of Nihon Parkerizing Co., Ltd.).
Thereafter, the steel sheets were spray-coated with "Palbond 3308"
(a tradename of Nihon Parkerizing Co., Ltd., an aqueous zinc
phosphate solution), washed with water and dried to obtain zinc
phosphate-treated plated steel sheets. The amount of the zinc
phosphate treatment coat was 1.5 g/m.sup.2.
[0176] The coating compositions were applied to the surfaces of the
zinc phosphate-treated plated steel sheets by spray coating so that
the dry film weight would be 1.0 g/m.sup.2, and baked for 20
seconds under such conditions that the substrate temperature became
100.degree. C., to form titanium oxide films.
[0177] (6) Corrosion Resistance of the Coated Sheets
[0178] The end faces and back face of the coated sheets were
sealed. The resulting sheets were subjected to the salt spray test
defined in JIS Z2371 for 24, 48 and 72 hours, and rated on the
following scale.
[0179] a: No white rusting;
[0180] b: Less than 5% of the coated surface area had white
rust;
[0181] c: Not less than 5% but less than 10% of the coated surface
area had white rust;
[0182] d: Not less than 10% but less than 50% of the coated surface
area had white rust;
[0183] e: 50% or more of the coated surface area had white
rust.
[0184] Table 4 shows the test results.
4 TABLE 4 Coating Test period composition 24 hr 48 hr 72 hr Ex. 1 a
a b Ex. 2 a a b Ex. 3 a a b Ex. 4 a a b Ex. 5 a a b Ex. 6 a b c Ex.
7 a b c Ex. 8 a b c Ex. 9 a b c Ex. 10 a b c Ex. 11 a a b Ex. 12 a
a a Ex. 13 a a a Ex. 14 a a a Ex. 15 a a a Ex. 16 a b c Ex. 17 a b
c Ex. 18 a b c Ex. 19 a b c Comp. Ex. 1 c d d Comp. Ex. 2 c c d
[0185] (7) Undercoating of Steel Sheets and Formation of Upper
Coats
[0186] Surfaces of hot rolled mild steel sheets (SPCC-SD) with a
thickness of 0.6 mm were degreased by spraying a 2% aqueous
solution of an alkaline degreasing agent (a product of Japan CB
Chemical Co., tradename "Chemicleaner 561B") at 65.degree. C. for
20 seconds, and washed by spraying warm water at 60.degree. C. for
20 seconds. The coating compositions were applied to the degreased
steel sheets by spray coating so that the dry film weight would be
1 g/m.sup.2, and baked in an atmosphere at 250.degree. C. for 15
seconds (the substrate temperature became 100.degree. C.), to form
titanium oxide films as undercoats.
[0187] "Amilac #1000 White" (a tradename of Kansai Paint Co., Ltd.,
a thermosetting alkyd resin coating composition, white) was applied
to the undercoated sheets so that the dry film weight would be 20
g/m2, baked at 130.degree. C. for 20 minutes to form upper coats,
and used as test coated sheets.
[0188] (8) Performance Test of the Test Coated Sheets
[0189] The test coated sheets were tested for corrosion resistance
and upper coat adhesion by the following methods.
[0190] Corrosion resistance: The end faces and back face of the
test coated sheets were sealed. On the coated surface of each test
coated sheet, a crosswise cut reaching the substrate was made using
a knife, and the resulting sheets were subjected to the salt spray
test defined in JIS Z2371 for 120 hours. After the test, adhesive
tape was applied to the crosswise cut portion on each test coated
sheet, and rapidly peeled off. The width of the peeled-off part of
the upper coat was rated on the following scale:
[0191] a: 1 mm or less;
[0192] b: 1 to 3 mm;
[0193] c: 3 to 5 mm;
[0194] d: 5 mm or more.
[0195] Upper coat adhesion: On the coated surface of each test
coated sheet, 11 each of vertical and horizontal cuts reaching the
substrate were made using a knife, to form 100 squares (1
mm.times.1 mm). Adhesive tape was applied to the cut portion, and
rapidly peeled off. Then, the degree of peeling of the upper coat
was rated on the following scale.
[0196] a: No peeling at all;
[0197] b: 1 or 2 squares peeled off;
[0198] c: 3 to 10 squares peeled off;
[0199] d: 10 or more squares peeled off.
[0200] Table 5 shows the test results.
5 TABLE 5 Corrosion Coating resistance Upper coat composition (120
hr) adhesion Ex. 1 b a Ex. 2 b a Ex. 3 b a Ex. 4 b a Ex. 5 b a Ex.
6 c a Ex. 7 c a Ex. 8 c a Ex. 9 c a Ex. 10 c a Ex. 11 b a Ex. 12 a
a Ex. 13 a a Ex. 14 a a Ex. 15 a a Ex. 16 c a Ex. 17 c a Ex. 18 c a
Ex. 19 c a Comp. Ex. 1 d b Comp. Ex. 2 d b
[0201] The coating composition for forming a titanium oxide film,
process for forming a titanium oxide film, and metal substrate
coated with a titanium oxide film according to the present
invention have the following remarkable effects.
[0202] (1) The coating composition of the present invention has
excellent storage stability. This is presumably because the
titanium-containing aqueous liquid (A) is stable by itself and
forms a stable complex with the organic acid and/or its salt
(B).
[0203] (2) The process using the coating composition of the present
invention is capable of forming, on a metal substrate, an amorphous
titanium oxide-containing film excellent in corrosion resistance,
adhesion, durability, processability, hydrophilicity and like
properties.
[0204] The excellent corrosion resistance and durability are
achieved presumably because: the film has good adhesion to the
substrate; the film is a dense titanium oxide film which has low
permeability to oxygen or water vapor; the organic acid and/or its
salt (B) coordinates to the metal substrate and functions as a
corrosion inhibitor for the metal; and titanium oxide protect the
component (B). The film has high adhesion presumably because the
titanium oxide in the film contains hydroxyl.
[0205] (3) A coated metal substrate obtained by the process of the
present invention can be advantageously used as a rust-resistant
coated substrate, without further treatment.
[0206] (4) A heat exchanger fin comprising an aluminum or aluminum
alloy substrate coated with a film formed from the coating
composition of the present invention is free from water bridges of
condensed water generated during cooling operation, and thus is
prevented from corroding.
* * * * *