U.S. patent application number 14/154677 was filed with the patent office on 2016-12-22 for corrosion-resistant trivalent-chromium chemical conversion coating and solution for trivalent-chromium chemical treatment.
This patent application is currently assigned to DIPSOL CHEMICALS CO., LTD.. The applicant listed for this patent is Toshiki Inomata, Manabu Inoue, Keita Ishizu, Go Nagata, Motoi Nakatani, Kimitaka Watanabe. Invention is credited to Toshiki Inomata, Manabu Inoue, Keita Ishizu, Go Nagata, Motoi Nakatani, Kimitaka Watanabe.
Application Number | 20160369107 14/154677 |
Document ID | / |
Family ID | 40341329 |
Filed Date | 2016-12-22 |
United States Patent
Application |
20160369107 |
Kind Code |
A9 |
Inoue; Manabu ; et
al. |
December 22, 2016 |
Corrosion-resistant trivalent-chromium chemical conversion coating
and solution for trivalent-chromium chemical treatment
Abstract
A trivalent-chromium chemical conversion coating from which
substantially no hexavalent chromium is released. The
trivalent-chromium chemical conversion coating is one formed on the
surface of a zinc or zinc-alloy deposit. In a brine spray test, the
chemical conversion coating has unsusceptibility to corrosion (time
required for white-rust formation) of 96 hours or longer. The
chemical conversion coating has a hexavalent-chromium concentration
less than 0.01 .mu.g/cm in terms of metal atom amount. The amount
of hexavalent chromium released after 30-day standing in a
thermo-hygrostatic chamber at a temperature of 80.degree. C. and a
humidity of 95% (amount of hexavalent chromium released when the
coating is immersed in 100.degree. C. water for 10 minutes) is
smaller than 0.05 .mu.g/cm.sup.2.
Inventors: |
Inoue; Manabu; (Tokyo,
JP) ; Watanabe; Kimitaka; (Tokyo, JP) ;
Nagata; Go; (Tokyo, JP) ; Nakatani; Motoi;
(Tokyo, JP) ; Ishizu; Keita; (Tokyo, JP) ;
Inomata; Toshiki; (Tokyo, JP) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Inoue; Manabu
Watanabe; Kimitaka
Nagata; Go
Nakatani; Motoi
Ishizu; Keita
Inomata; Toshiki |
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo
Tokyo |
|
JP
JP
JP
JP
JP
JP |
|
|
Assignee: |
DIPSOL CHEMICALS CO., LTD.
Tokyo
JP
|
Prior
Publication: |
|
Document Identifier |
Publication Date |
|
US 20140124099 A1 |
May 8, 2014 |
|
|
Family ID: |
40341329 |
Appl. No.: |
14/154677 |
Filed: |
January 14, 2014 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
12671786 |
Mar 10, 2010 |
|
|
|
PCT/JP2008/063963 |
Aug 4, 2008 |
|
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14154677 |
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Current U.S.
Class: |
1/1 |
Current CPC
Class: |
Y10T 428/273 20150115;
C09D 5/08 20130101; C23C 28/3225 20130101; C23C 22/77 20130101;
C23C 22/40 20130101; C23C 22/33 20130101; C23C 28/34 20130101; C23C
2222/10 20130101; C23C 22/47 20130101; C23C 22/27 20130101; C23C
22/83 20130101; C23C 22/30 20130101; C23C 22/46 20130101; C23C
22/53 20130101 |
International
Class: |
C09D 5/08 20060101
C09D005/08 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 3, 2007 |
JP |
2007-203284 |
Nov 16, 2007 |
JP |
2007-298411 |
Claims
1-19. (canceled)
20-23. (canceled)
24. A chemical conversion treatment liquid for forming a trivalent
chromium chemical conversion coating film on zinc or zinc alloy
plating, characterized in that a content of trivalent chromium ions
in the treatment liquid is 0.002 to 0.5 mol/l, a concentration of
hexavalent chromium ions is 1 ppm or less, a content of cobalt ions
is 0.1 mol/1 or less, a hexavalent chromium generation suppressing
agent that can suppress generation of hexavalent chromium which is
generated in the trivalent chromium chemical conversion coating
film is contained in said liquid, and a pH of the chemical
conversion treatment liquid is 0.5 to 5.
25. The chemical conversion treatment liquid according to claim 24,
wherein the hexavalent chromium generation suppressing agent is
within the range of 0.1 to 5 g/l.
26. The chemical conversion treatment liquid according to claim 24,
wherein the hexavalent chromium generation suppressing agent is a
reducing compound.
27. The chemical conversion treatment liquid according to claim 24,
wherein the hexavalent chromium generation suppressing agent is
selected from the group consisting of a tannic acid and a salt
thereof, gallic acid and a salt thereof, tartaric acid and a salt
thereof, citric acid and a salt thereof, ascorbic acid and a salt
thereof, a vanadium compound, a titanium compound, phosphoric acid
and a salt thereof, and chromium phosphate.
28. The chemical conversion treatment liquid according to claim 24,
further comprising a chelating agent in the range of 0.2 to 2 mole
per mole of Cr3+.
29. The chemical conversion treatment liquid according to claim 24,
wherein a content of nitrogen is 500 ppm or less in terms of
nitrogen atoms.
30. The chemical conversion treatment liquid according to claim 24,
further comprising a quinoline-based compound or a derivative
thereof.
31. Washing water or a finishing liquid for a trivalent chromium
chemical conversion coating film formed on zinc plating or zinc
alloy plating, characterized by comprising a hexavalent chromium
generation suppressing agent that can suppress generation of
hexavalent chromium which is generated in the trivalent chromium
chemical conversion coating film at 0.1 to 10 g/l, wherein a pH of
the washing water or the finishing liquid is 2 to 10.
32. A chemical conversion treatment liquid for forming a trivalent
chromium chemical conversion coating film on zinc or zinc alloy
plating, characterized in that a content of trivalent chromium ions
in the treatment liquid is 0.002 to 0.5 mol/l, a concentration of
hexavalent chromium ions is 1 ppm or less, a content of cobalt ions
is 250 ppm or less, and a sulfur compound is contained in the range
of 100 to 1500 ppm in terms of sulfur atoms.
33. The chemical conversion treatment liquid according to claim 32,
wherein a content of nitrogen is 500 ppm or less in terms of
nitrogen atoms.
34. The chemical conversion treatment liquid according to claim 32,
further comprising a silicon compound.
35. The chemical conversion treatment liquid according to claim 32,
further comprising a quinoline-based compound or a derivative
thereof.
36-37. (canceled)
38. The trivalent chromium chemical conversion coating film,
wherein a corrosion resistance (a time required for the formation
of white rust) in a salt spray test is 96 hours or more, a
concentration of hexavalent chromium in terms of metal atoms in the
chemical conversion coating film is less than 0.01 .mu.g/cm2, and
an amount of hexavalent chromium eluted from the coating film left
for 30 days in a constant temperature and humidity chamber at a
temperature of 80.degree. C. and at a humidity of 95% (an amount
eluted by immersion of the coating film into hot water at a
temperature of 100.degree. C. for 10 minutes) is less than 0.05
.mu.g/cm2, wherein the trivalent chromium chemical conversion
coating film is formed on zinc or zinc alloy plating, and after the
formation thereof, the coating film is treated with the washing
water or the finishing liquid; comprising: a hexavalent chromium
generation suppressing agent that can suppress generation of
hexavalent chromium which is generated in the trivalent chromium
chemical conversion coating film at 0.1 to 10 g/l, wherein a pH of
the washing water or the finishing liquid is 2 to 10.
Description
TECHNICAL FIELD
[0001] The present invention relates to a trivalent chromium
corrosion resistant chemical conversion treatment coating film from
which hexavalent chromium is not substantially eluted, the coating
film being formed on zinc plating or zinc alloy plating, and a
trivalent chromium chemical conversion treatment solution and a
post-treatment solution after chemical conversion treatment used to
form such a chemical conversion treatment coating film.
BACKGROUND ART
[0002] A method using zinc plating has been relatively widely
employed as a method for inhibiting corrosion of the surface of a
metal. However, the plating by itself does not provide a sufficient
corrosion resistance, and thus a chromate treatment using
hexavalent chromium after plating has been widely employed in
industry. However, it has been pointed out in recent years that
hexavalent chromium harms human bodies and the environment, and, as
a result, the use of hexavalent chromium has been regulated.
[0003] In this connection, a trivalent chromium chemical conversion
coating film using trivalent chromium has been developed as an
alternative technology to a coating film formed with hexavalent
chromium, and has started to be used. For example, Japanese Patent
Application Publication No. 2000-509434 discloses a treatment
method in which 5 to 100 g/L of trivalent chromium, nitrate, an
organic acid and a salt of a metal such as cobalt are used. This
method is to obtain a good corrosion resistance by carrying out the
treatment at an elevated temperature in high concentration of
chromium to form a thick trivalent chromium chemical conversion
coating film. However, the method has disadvantage in wastewater
treatment, because the concentration of chromium and the
concentration of the organic acid in the treatment bath are high.
[0004] Patent Article 1: Japanese Patent Application Publication
No. 2000-509434
DISCLOSURE OF THE INVENTION
[0005] In addition, it has been found out that there is a problem
that, when such a conventional hexavalent chromium-free trivalent
chromium chemical conversion treatment coating film is left for a
long period in a natural environment, trivalent chromium in the
coating film is oxidized, and harmful hexavalent chromium is
detected in the coating film.
[0006] An object of the present invention is to provide a trivalent
chromium corrosion resistant chemical conversion treatment coating
film being formed on zinc or zinc-based alloy plating, and having a
corrosion resistance equal to or more than a conventional coating
film with a low chromium content. Moreover, in consideration of
effect on human bodies and the environment, hexavalent chromium is
not substantially detected in the coating film even after the
coating film is left. In addition, another object of the present
invention is to provide a trivalent chromium chemical conversion
treatment solution and a post-treatment solution used after
chemical conversion treatment, the treatment solution and the
post-treatment solution being capable of forming such a chemical
conversion treatment coating film.
[0007] The present inventors have made a thorough examination and
found that a chemical conversion coating film that has a high
corrosion resistance and from which hexavalent chromium is
substantially not eluted even after the coating film is left can be
obtained from a trivalent chromium chemical conversion coating film
having low trivalent chromium concentration if the coating film
itself is provided with a function of suppressing oxidation from
trivalent chromium in the coating film to hexavalent chromium. In
addition, the present inventors also found that such a chemical
conversion coating film can be obtained by using a chemical
conversion treatment liquid having a specific composition.
[0008] Accordingly, the present invention is a trivalent chromium
chemical conversion coating film formed on a surface of zinc or
zinc alloy plating characterized in that a corrosion resistance (a
time required for the formation of white rust) in a salt spray test
is 96 hours or more, a concentration of hexavalent chromium in
terms of metal atoms in the chemical conversion coating film is
less than 0.01 .mu.g/cm.sup.2, and an amount of hexavalent chromium
eluted from the coating film left for 30 days in a constant
temperature and humidity chamber at a temperature of 80.degree. C.
and at a humidity of 95% (an amount eluted by immersion of the
coating film into hot water at a temperature of 100.degree. C. for
10 minutes) is less than 0.05 .mu.g/cm.sup.2.
[0009] A preferred aspect of the present invention is the
above-descried trivalent chromium chemical conversion coating film,
in which a concentration of trivalent chromium in terms of metal
atoms in the chemical conversion coating film is 2 to 20
.mu.g/cm.sup.2.
[0010] In addition, the trivalent chromium chemical conversion
coating film, in which a cobalt concentration in the chemical
conversion coating film is 0.2 to 3.5 .mu.g/cm.sup.2, is an aspect
of the present invention. In this aspect, a preferable cobalt
concentration is 0.3 to 3 .mu.g/cm.sup.2.
[0011] Furthermore, the trivalent chromium chemical conversion
coating film, in which a cobalt concentration in the chemical
conversion coating film is less than 0.2 .mu.g/cm.sup.2, is an
aspect of the present invention. In this aspect, a preferable
cobalt concentration is 0 to 0.17 .mu.g/cm.sup.2.
[0012] The reason why the chemical conversion coating film that
have a high corrosion resistance and from which hexavalent chromium
is substantially not eluted even after the coating film is left can
be obtained by providing the coating film itself with a function of
suppressing oxidation from trivalent chromium in the coating film
to hexavalent chromium is not clear. However, through the
investigation in the present invention, the present inventors
assume that the reason is as follows. Specifically, it is assumed
that detection of hexavalent chromium from a generally used
trivalent chromium chemical conversion coating film which is being
left is caused because Co.sup.3+ in the chemical conversion coating
film acts as an oxidizing agent to oxidize trivalent chromium.
[0013] Formation of a trivalent chromium chemical conversion
coating film and an assumed generation mechanism of Cr.sup.6+ by
action of Co.sup.3+ will be described below.
(i) Zinc is dissolved in an acidic treatment liquid, and electrons
are released.
Zn.fwdarw.Zn.sup.2++2e.sup.-
(ii) Hydrogen ions are consumed at the interface between the zinc
and the treatment liquid, and the pH of the treatment liquid
rises.
2H.sup.++2e.sup.-.fwdarw.H.sub.2.uparw.
(iii) Chromium hydroxide is generated by the rise of pH of the
treatment liquid.
2Cr.sup.3++6(OH.sup.-).fwdarw.2Cr(OH).sub.3.uparw.
(iv) Also from Co.sup.2+ that is used for improving the corrosion
resistance in the treatment liquid, cobalt(II) hydroxide is
generated in the vicinity of the interface with the zinc with the
rise of pH. However, Co.sup.2+ is converted to stable Co.sup.3+
with time, because Co.sup.2+ is unstable on the alkaline side.
Co(OH).sub.2.fwdarw.Co(OH).sub.3
(v) Other insoluble substances (SiO.sub.2) and a small amount of
the treatment liquid are also adsorbed and impregnated to be taken
into the coating film, with gelation and deposition of chromium
hydroxide and cobalt hydroxide (Co.sup.2+, Co.sup.3+). (vi) The
coating film is hardened in drying processes by deposition,
dewatering of adsorbed substances and solidification. However, the
coating film is not hardened when the drying is insufficient, and
it is expected that chemical reactions will proceed in the coating
film. (vii) Since the chemical conversion coating film containing
the treatment liquid is in a slightly acidic atmosphere, cobalt
(III) hydroxide in the coating film is gradually liberated and
dissolved, and Co.sup.3+ is converted to Co.sup.2+ that is stable
in an acidic condition. In addition, it is considered that chromium
hydroxide is also liberated and dissolved to cause the following
reactions.
3Co.sup.3++3e.sup.-.fwdarw.3Co.sup.2+
Cr.sup.3+.fwdarw.Cr.sup.6++3e.sup.-
[0014] Combination of these formulae gives the following.
Cr.sup.3++3Co.sup.3+.fwdarw.Cr.sup.6++3Co.sup.2+
[0015] In short, it is considered that trivalent cobalt in the
coating film oxidizes trivalent chromium to generate hexavalent
chromium.
[0016] Meanwhile, it is considered that, even when Co.sup.3+ is not
contained or even when the coating film is formed from a chemical
conversion treatment liquid having a strong oxidizing effect caused
by a combination of chloric acid-nitric acid, or the like,
hexavalent chromium is generated. Therefore, it is assumed that
reduction of nitrate ion concentration in the treatment liquid is
also helps to suppress the generation of hexavalent chromium. It is
considered that, in a chemical conversion coating film containing a
manganese compound such as manganese dioxide, and in a chemical
conversion coating film containing, in the coating film, a large
amount of ions of an element other than Co whose valence can vary,
hexavalent chromium is generated by oxidation of trivalent chromium
in a similar manner.
[0017] In addition, the present invention is achieved on the basis
of the following discovery. Specifically, by adding a hexavalent
chromium generation suppressing agent having an effect of
suppressing hexavalent chromium generation to any one of a
trivalent chromium chemical conversion treatment liquid, washing
water for a trivalent chromium chemical conversion coating film and
a finishing liquid therefor, hexavalent chromium which is otherwise
generated in the trivalent chromium chemical conversion coating
film can be suppressed, and an amount of hexavalent chromium eluted
from the trivalent chromium chemical conversion coating film (an
amount eluted when the coating film is immersed in a hot water at a
temperature of 100.degree. C. for 10 minutes) can be less than 0.05
.mu.g/cm.sup.2 even after the coating film is left.
[0018] Therefore, the present invention provides a chemical
conversion treatment liquid for forming, on zinc or zinc alloy
plating, a trivalent chromium chemical conversion coating film from
which hexavalent chromium is substantially not eluted even after
the coating film is left. The chemical conversion treatment liquid
is characterized in that a content of trivalent chromium ions in
the treatment liquid is 0.002 to 0.5 mol/l, a concentration of
hexavalent chromium ions is 1 ppm or less, a content of cobalt ions
is 0.1 mol/l or less, a hexavalent chromium generation suppressing
agent that can suppress generation of hexavalent chromium which is
generated in the trivalent chromium chemical conversion coating
film is contained in said liquid, and a pH of the chemical
conversion treatment liquid is 0.5 to 5.
[0019] In addition, the present invention provides washing water or
a finishing liquid for a trivalent chromium chemical conversion
coating film formed on zinc or zinc alloy plating, for suppressing
hexavalent chromium which is otherwise generated in the trivalent
chromium chemical conversion coating film. The washing water or the
finishing liquid is characterized by containing a hexavalent
chromium generation suppressing agent that can suppress generation
of hexavalent chromium which is generated in the trivalent chromium
chemical conversion coating film at 0.1 to 10 g/l, and
characterized in that a pH of the washing water or the finishing
liquid is 2 to 10.
[0020] In addition, the present invention is achieved on the basis
of the following discovery. Specifically, a trivalent chromate
coating film is formed by use of a trivalent chromium chemical
conversion treatment liquid in which a content of cobalt ions is
250 ppm or less and a content of a sulfur compound is in the range
of 100 to 1000 ppm in terms of sulfur atoms. As a result,
hexavalent chromium which is otherwise generated in the trivalent
chromium chemical conversion coating film can be suppressed, and an
amount of hexavalent chromium eluted from the trivalent chromium
chemical conversion coating film can be less than 0.05
.mu.g/cm.sup.2 even after the coating film is left (an amount
eluted when the coating film is immersed in hot water at a
temperature of 100.degree. C. for 10 minutes).
[0021] Therefore, the present invention provides a chemical
conversion treatment liquid for forming a trivalent chromate
coating film from which hexavalent chromium is not substantially
eluted after the coating film is left, the trivalent chromate
coating film being formed on zinc or zinc alloy plating. The
chemical conversion treatment liquid is characterized in that a
content of trivalent chromium ions in the treatment liquid is 0.002
to 0.5 mol/l, a concentration of hexavalent chromium ions is 1 ppm
or less, a content of cobalt ions is 250 ppm or less, and a sulfur
compound is contained in the range of 100 to 1500 ppm in terms of
sulfur atoms.
[0022] The trivalent chromium chemical conversion coating film
according to the present invention further has an excellent
corrosion resistance of the trivalent chromium chemical conversion
coating film, in addition to a corrosion resistance of zinc plating
itself. In addition, the coating film obtained by forming the
trivalent chromium chemical conversion coating film directly on
zinc plating undergoes no substantial elution of hexavalent
chromium after the coating film is left, has a corrosion resistance
and a salt water resistance equal to or higher than those of
conventional hexavalent chromate, and can be applied in various
colors. In addition, in the chemical conversion treatment liquid
according to the present invention that can form such a chemical
conversion coating film, the trivalent chromium concentration in
the treatment liquid is low, and an organic acid concentration or
nitrogen concentration can also further be reduced. Therefore, the
treatment liquid is advantageous in wastewater treatment and thus
has excellent cost performance.
BEST MODE FOR CARRYING OUT THE INVENTION
[0023] The substrate used in the present invention may be made of
any of the following materials: various metals such as iron, nickel
and copper; alloys thereof; and metals and alloys such as aluminum,
which have been subjected to zincate conversion treatment, and may
have any of various shapes such as plate-like, rectangular,
column-like, cylindrical and spherical shapes.
[0024] The above substrate is plated with zinc or a zinc alloy by
the usual method. The zinc plating may be deposited on the
substrate using either of the following baths: an acidic/neutral
bath such as a sulfuric acid bath, a borofluoride bath, a potassium
chloride bath, a sodium chloride bath or an ammonium
chloride-potassium chloride bath; or an alkaline bath such as a
cyanide bath, a zincate bath or a pyrophoric acid bath, but
particularly, a cyanide bath is preferable. The zinc alloy plating
may be performed using either an ammonium chloride bath or an
alkaline bath such as an organic chelate bath.
[0025] In addition, the zinc alloy plating may be zinc-iron alloy
plating, zinc-nickel alloy plating, zinc-cobalt alloy plating or
tin-zinc alloy plating. Zinc-iron alloy plating is preferable. The
zinc or zinc alloy plating may be deposited on a substrate in any
thickness, but preferably in a thickness of 1 .mu.m or more, and
more preferably in a thickness of 5 to 25 .mu.m.
[0026] In the present invention, after the zinc or zinc alloy
plating is deposited on a substrate according to the above method,
the plated substrate is appropriately pretreated by, for example,
being washed with water and optionally activated by a nitric acid,
as needed. Thereafter, the zinc or zinc alloy plating is subjected
to chemical conversion treatment by a dipping treatment, or the
like using a chemical conversion treatment liquid for forming the
trivalent chromium chemical conversion coating film according to
the present invention.
[0027] The chemical conversion treatment liquid of the first aspect
of the present invention contains trivalent chromium ions, cobalt
ions and hexavalent chromium generation suppressing agent that can
suppress generation of hexavalent chromium which is otherwise
generated in the trivalent chromium chemical conversion coating
film.
[0028] In the chemical conversion treatment liquid, any chromium
compound containing trivalent chromium ions may be used as a source
of trivalent chromium ions. For example, the sources of trivalent
chromium salts such as chromium chloride, chromium sulfate,
chromium nitrate, chromium phosphate or chromium acetate can be
used, or, alternatively, trivalent chromium ions can be obtained by
the reduction of hexavalent chromium ions of chromic acid, a
dichromate, or the like with a reducing agent. However, the sources
are not limited to these examples. One of the above sources of
trivalent chromium ions or any combination of at least two of them
may be used. A content of trivalent chromium ions in the chemical
conversion treatment liquid should preferably be 0.002 to 0.5
mol/l, and should more preferably be 0.02 to 0.1 mol/l. Meanwhile,
a concentration of hexavalent chromium ions in the chemical
conversion treatment liquid should preferably be 1 ppm or less, and
should more preferably be 0.5 ppm or less.
[0029] In the chemical conversion treatment liquid, any metal
compound containing cobalt may be used as a source of cobalt ions.
Examples of such metal compounds include cobalt nitrate, cobalt
sulfate, cobalt chloride, cobalt carbonate and cobalt hydroxide.
However, the metal compounds are not limited to these examples. One
of the above metal compounds or any combination of at least two of
them may be used. A content of cobalt ions in the chemical
conversion treatment liquid should preferably be 0.1 mol/l or less,
should more preferably be 0.001 to 0.06 mol/l, and should still
more preferably be 0.005 to 0.04 mol/l.
[0030] In the chemical conversion treatment liquid, any additives
can be used as the hexavalent chromium generation suppressing agent
as long as the additives can suppress generation of hexavalent
chromium which is otherwise generated in the trivalent chromium
chemical conversion coating film. In order to find out additives
that can suppress generation of hexavalent chromium, various
additives are added to chemical conversion treatment liquids for
forming the trivalent chromate coating film and effect of the
additives is examined by experiments. As a result, organic reducing
compounds such as ascorbate ions, citrate ions, tannate ions,
gallate ions, tartrate ions, hydroxy(iso)quinolines, phenols and
thiourea, and inorganic or metal reducing compounds such as
phosphate ions, chromium phosphate ions, vanadium ions and titanium
ions show the effect. Therefore, preferable hexavalent chromium
generation suppressing agents include ascorbic acid, salts thereof,
citric acid, salts thereof, tannic acid, salts thereof, gallic
acid, salts thereof, tartaric acid, salts thereof, thiourea,
phosphoric acid, salts thereof, vanadium compounds, titanium
compounds, and the like. A content of the hexavalent chromium
generation suppressing agent in the chemical conversion treatment
liquid should preferably be 0.1 to 5 g/l, should more preferably be
0.2 to 3 g/l, and should still more preferably be 0.3 to 2 g/l.
[0031] A pH of the chemical conversion treatment liquid should
preferably be 0.5 to 5, and should more preferably be 2 to 3. The
pH can be adjusted to this range by using the inorganic acid ions
as described below, and also by using an alkaline agent such as an
alkaline hydroxide, ammonia water, or the like.
[0032] The chemical conversion treatment liquid may contain one or
more kinds selected from inorganic acids, alkaline salts thereof,
and the like. Examples of inorganic acids include sulfuric acid,
nitric acid, hydrochloric acid, and the like. However, the
inorganic acids are not limited to these examples. When one or more
kinds selected from inorganic acids, alkaline salts thereof, and
the like are contained, a concentration thereof in the chemical
conversion treatment liquid should preferably be 1 to 50 g/L, and
should more preferably be 4 to 20 g/L.
[0033] In addition, the chemical conversion treatment liquid may
contain one or more kinds of hydroxycarboxylic acids,
monocarboxylic acids, polyvalent carboxylic acids, aminocarboxylic
acids, alkaline salts thereof, and the like as chelating agents for
trivalent chromium ions. Examples of hydroxycarboxylic acids
include malic acid, and the like. However, the hydroxycarboxylic
acids are not limited to these examples. Examples of monocarboxylic
acids include formic acid, acetic acid, and the like. However, the
monocarboxylic acids are not limited to these examples. Examples of
polyvalent carboxylic acids include: dicarboxylic acids such as
oxalic acid, malonic acid, succinic acid, adipic acid and
diglycolic acid; tricarboxylic acids such as propanetricarboxylic
acid, and the like. However, the polyvalent carboxylic acids are
not limited to these examples. Examples of aminocarboxylic acids
include glycine, aspartic acid, and the like. However, the
aminocarboxylic acids are not limited to these examples. Among
these, polyvalent carboxylic acids are preferable, and oxalic acid,
malonic acid and succinic acid are more preferable. When the
chelating agent for trivalent chromium ions is contained, a
concentration thereof in the chemical conversion treatment liquid
should preferably be in the range of 0.2 to 2 mole, should more
preferably be in the range of 0.3 to 2 mole, should still more
preferably be in the range of 0.5 to 2 mole, and should still
further more preferably be in the range of 0.7 to 1.8 mole per mole
of trivalent chromium ions.
[0034] In addition, the chemical conversion treatment liquid may
contain one or more kinds of silicon compounds. Examples of silicon
compounds include colloidal silica, sodium silicate, potassium
silicate, lithium silicate, and the like. However, the silicon
compounds are not limited to these examples. When the silicon
compound is contained, a concentration thereof in the chemical
conversion treatment liquid should preferably be 1 to 20 g/l, and
should more preferably be 2 to 10 g/l in terms of Si. Colloidal
silica is particularly preferable. A concentration thereof should
preferably be 1 to 100 ml/l as a 20% SiO2 aqueous solution. By
adding colloidal silica, a coating film with a bilayer structure of
a Si--O layer and a Cr--O layer can be formed, whereby the
corrosion resistance can be further improved.
[0035] In addition, the chemical conversion treatment liquid may
contain one or more kinds of agents for reducing a coating film
overall friction coefficient. Examples of such agents for reducing
a coating film overall friction coefficient include quinoline-based
compounds such as quinoline sulfonic acid, quinaldic acid,
quinophthalone and derivatives thereof described in Japanese Patent
Application Publication No. 2005-248233. When the agent for
reducing a coating film overall friction coefficient is contained,
a concentration thereof in the chemical conversion treatment liquid
should preferably be 0.1 to 25 g/l, and should more preferably be
0.2 to 15 g/l. The trivalent chromium chemical conversion coating
film according to the present invention formed by treatment with
the chemical conversion treatment liquid containing such a agent
for reducing a coating film overall friction coefficient is a
coating film that has a reduced coating film overall friction
coefficient.
[0036] The rest of the chemical conversion treatment liquid other
than the above essential components is water.
[0037] Usually, a nitrogen-containing compound, mainly nitrate
ions, is used in large amount in a trivalent chromium chemical
conversion treatment liquid, for improving the corrosion resistance
of a trivalent chromium chemical conversion coating film.
Consequently, the nitrogen atom concentration in the treatment
liquid is high, for example 3 to 9 g/l, and there is a problem in
terms of the wastewater treatment. In the chemical conversion
treatment liquid according to the present invention, nitrate ions
may be used in an amount similar to a conventional treatment
liquid. However, even when nitrate ions are considerably decreased,
and a nitrogen atom concentration, in the chemical conversion
treatment liquid, mainly derived from nitrate ions is considerably
reduced to 500 ppm/1 or less, the trivalent chromium chemical
conversion coating film that has an excellent corrosion resistance
and from which elution of hexavalent chromium is suppressed when
the coating film is left can be obtained from the chemical
conversion treatment liquid. In the above treatment liquid, a
content is specifically 500 ppm or less in terms of nitrogen atoms,
should preferably be in the range of 30 to 400 ppm and should more
preferably be in the range of 50 to 300 ppm, for example. A metal
reducing compound is preferable as the hexavalent chromium
generation suppressing agent. Particularly, vanadium compounds,
titanium compounds, magnesium compounds and combination thereof are
preferable.
[0038] In addition, cobalt ions may be contained but are not
necessarily contained. However, cobalt ions should be contained
preferably in the range of 0.001 to 0.06 mol/l, and more preferably
in the range of 0.005 to 0.04 mol/l, because corrosion resistance
of the chemical conversion coating film under heating is further
improved.
[0039] A method for forming a trivalent chromium chemical
conversion coating film on zinc or zinc alloy plating by using the
chemical conversion treatment liquid is commonly to immerse a zinc
or zinc alloy plated substrate into the chemical conversion
treatment liquid. A temperature of the chemical conversion
treatment liquid at immersion is, for example, 10 to 70.degree. C.
The temperature should preferably be 30 to 50.degree. C. An
immersion time should preferably be 5 to 600 seconds, and should
more preferably be 15 to 120 seconds. Meanwhile, immersion into a
diluted nitric acid solution, a diluted sulfuric acid solution, a
diluted hydrochloric acid solution, a diluted hydrofluoric acid
solution, or the like may be performed before trivalent chromium
chemical conversion treatment, for activating the surface of the
zinc or zinc alloy plating. The conditions and treatment operations
other than those described above may follow the conventional
hexavalent chromate treatment method.
[0040] Meanwhile, the second aspect of the present invention is
washing water or a finishing liquid for a trivalent chromium
chemical conversion coating film formed on zinc or zinc alloy
plating. The washing water or the finishing liquid is used for
suppressing hexavalent chromium which is otherwise generated in the
trivalent chromium chemical conversion coating film. The washing
water or the finishing liquid contains a hexavalent chromium
generation suppressing agent that can suppress generation of
hexavalent chromium which is otherwise generated in the trivalent
chromium chemical conversion coating film. A method for forming a
trivalent chromium chemical conversion coating film to which the
washing water or the finishing liquid is applied is not
particularly limited, and may be any known method. The washing
water or the finishing liquid is particularly effective in the
following cases: the trivalent chromium chemical conversion coating
film contains Co.sup.2+ and Co.sup.3+; the trivalent chromium
chemical conversion coating film is a coating film formed from a
chemical conversion treatment liquid having a stronger oxidizing
effect caused by a combination of chloric acid-nitric acid, or the
like; the trivalent chromium chemical conversion coating film
contains a manganese compound such as manganese dioxide; and the
trivalent chromium chemical conversion coating film contains, in
the coating film, a large amount of ions of an element, other than
Co, whose valence can vary. Meanwhile, the hexavalent chromium
generation suppressing agent is already described above. A content
of the hexavalent chromium generation suppressing agent in the
washing water or the finishing liquid should preferably be 0.1 to
10 g/l, should more preferably be 0.2 to 5 g/l, and should still
more preferably be 0.3 to 3 g/l. Examples of preferable hexavalent
chromium generation suppressing agents include ascorbic acid, salts
thereof, citric acid, salts thereof, tannic acid, salts thereof,
gallic acid, salts thereof, tartaric acid, salts thereof, thiourea,
phosphoric acid, salts thereof, and the like.
[0041] A pH of the washing water or the finishing liquid should
preferably be 2 to 10, and should more preferably be 3 to 6. The pH
may be adjusted to this range by using the inorganic acid ions as
described below, or by using an alkaline agent such as an alkaline
hydroxide, ammonia water, or the like.
[0042] A method for treating a trivalent chromium chemical
conversion coating film using the washing water or the finishing
liquid is not particularly limited, and conventional and known
methods such as immersing, applying, spraying, and the like may be
used. However, to immerse a trivalent chromium chemical conversion
coating film into the washing water or the finishing liquid is
commonly employed. A temperature of the washing water or the
finishing liquid at immersion is, for example, 10 to 70.degree. C.
The temperature should preferably be 20 to 50.degree. C. An
immersion time should preferably be 5 to 120 seconds, and should
more preferably be 5 to 15 seconds.
[0043] Meanwhile, a chemical conversion treatment liquid of the
third aspect of the present invention contains trivalent chromium
ions, cobalt ions and a sulfur compound.
[0044] In the chemical conversion treatment liquid, any chromium
compound containing trivalent chromium ions may be used as a source
of trivalent chromium ions. For example, the source should be
trivalent chromium salt such as chromium chloride, chromium
sulfate, chromium nitrate, chromium phosphate or chromium acetate,
or, alternatively, trivalent chromium ions can be obtained by the
reduction of hexavalent chromium ions of chromic acid, a
dichromate, or the like with a reducing agent. However, the source
is not limited to these examples. One of the above sources of
trivalent chromium ions or any combination of at least two of them
may be used. A content of trivalent chromium ions in the chemical
conversion treatment liquid should preferably be 0.002 to 0.5
mol/l, and should more preferably be 0.02 to 0.1 mol/l. Meanwhile,
a concentration of hexavalent chromium ions in the chemical
conversion treatment liquid should preferably be 1 ppm or less, and
should more preferably be 0.5 ppm or less.
[0045] A content of cobalt ions in the chemical conversion
treatment liquid is 250 ppm or less. The chemical conversion
treatment liquid does not necessarily contain cobalt ions. Since
the sulfur compound is contained, the formed trivalent chromium
chemical conversion coating film has a sufficient corrosion
resistance even when cobalt ions are not contained. A content of
cobalt ions in the chemical conversion treatment liquid should
preferably be 100 to 250 ppm, and should more preferably be 150 to
200 ppm, when a higher corrosion resistance is required. When the
chemical conversion treatment liquid contains cobalt ions, any
metal compound containing cobalt can be used as a source of cobalt
ions. Examples of such metal compounds include cobalt nitrate,
cobalt sulfate, cobalt chloride, cobalt carbonate and cobalt
hydroxide. However, the metal compounds are not limited to these
examples. One of the above metal compounds or any combination of at
least two of them may be used.
[0046] In the chemical conversion treatment liquid, an organic
sulfur compound is preferable as the sulfur compound. Specific
examples of organic sulfur compounds include thiourea,
thioglycerin, thioacetic acid, potassium thioacetate, thiodiacetic
acid, 3,3-thiodipropionic acid, thiosemicarbazide, thioglycolic
acid, thiodiglycolic acid, thiomaleic acid, thioacetamide,
dithioglycolic acid, dithiodiglycolic acid, alkaline salts thereof,
and the like. In addition, one of the above sulfur compounds or a
mixture of two or more of them can be used. A content of the sulfur
compound in the chemical conversion treatment liquid should
preferably be 100 to 1500 ppm, should more preferably be 300 to
1000 ppm, and should still more preferably be 400 to 800 ppm in
terms of sulfur atoms. By adding the sulfur compound, the formed
trivalent chromium chemical conversion coating film has a
sufficient corrosion resistance, even when a concentration of
cobalt ions in the coating film is 0.2 .mu.g/cm or less, and
preferably 0.17 .mu.g/cm or less. In addition, in the trivalent
chromium chemical conversion coating film formed from the chemical
conversion treatment liquid, hexavalent chromium which is otherwise
generated in the trivalent chromium chemical conversion coating
film can be suppressed because of low concentration of cobalt ions
in the coating film.
[0047] In the chemical conversion treatment liquid, a high
corrosion resistance can be maintained even when nitrogen content
in the treatment liquid is considerably reduced. A preferable
nitrogen content is 500 ppm or less, and preferably 200 ppm or less
in terms of nitrogen atoms. The content should more preferably be
40 to 200 ppm, and should still more preferably be 60 to 130
ppm.
[0048] In addition, the chemical conversion treatment liquid may
contain one or more kinds of silicon compounds. Examples of silicon
compounds include colloidal silica, sodium silicate, potassium
silicate, lithium silicate, and the like. However, the silicon
compounds are not limited to these examples. When the silicon
compound is contained, a concentration thereof in the chemical
conversion treatment liquid should preferably be 1 to 20 g/l, and
should more preferably be 2 to 10 g/l in terms of Si. Colloidal
silica is particularly preferable. A concentration thereof should
preferably be 1 to 100 ml/l as a 20% SiO.sub.2 aqueous solution. By
adding colloidal silica, a coating film with a bilayer structure of
a Si--O layer and a Cr--O layer can be formed, whereby corrosion
resistance can be further improved.
[0049] In addition, the chemical conversion treatment liquid may
contain one or more kinds of agents for reducing a coating film
overall friction coefficient. Examples of such agents for reducing
a coating film overall friction coefficient include quinoline-based
compounds such as quinoline sulfonic acid, quinaldic acid,
quinophthalone and derivatives thereof described in Japanese Patent
Application Publication No. 2005-248233. When the agent for
reducing a coating film overall friction coefficient is contained,
a concentration thereof in the chemical conversion treatment liquid
should preferably be 0.1 to 25 g/l, and should more preferably be
0.2 to 15 g/l. The trivalent chromium chemical conversion coating
film according to the present invention formed by treatment with
the chemical conversion treatment liquid containing such a agent
for reducing a coating film overall friction coefficient is a
coating film that has a reduced coating film overall friction
coefficient.
[0050] In addition, the chemical conversion treatment liquid may
contain one or more kinds selected from inorganic acids, alkaline
salts thereof, and the like. Examples of inorganic acids include
sulfuric acid, nitric acid, hydrochloric acid, and the like.
However, the inorganic acids are not limited to these examples.
When one or more kinds selected from inorganic acids, the alkaline
salts thereof, and the like are contained, a concentration thereof
in the chemical conversion treatment liquid should preferably be
0.01 to 50 g/L, and should more preferably be 0.05 to 20 g/L.
[0051] In addition, the chemical conversion treatment liquid may
contain one or more kinds selected from phosphorus oxoacids such as
hypophosphorous acid, phosphoric acid, alkaline salts thereof, and
the like. When one or more kinds selected from phosphorus oxoacids
such as hypophosphorous acid, phosphoric acid, alkaline salts
thereof, and the like are contained, the concentration thereof in
the chemical conversion treatment liquid should preferably be 0.1
to 50 g/L, and should more preferably be 4 to 25 g/L.
[0052] Furthermore, the chemical conversion treatment liquid may
contain one or more kinds of hydroxycarboxylic acids,
monocarboxylic acids, polyvalent carboxylic acids, aminocarboxylic
acids, alkaline salts thereof, and the like as chelating agents for
trivalent chromium ions. Examples of hydroxycarboxylic acids
include malic acid, and the like. However, the hydroxycarboxylic
acids are not limited to these examples. Examples of monocarboxylic
acids include formic acid, acetic acid, and the like. However, the
monocarboxylic acids are not limited to these examples. Examples of
polyvalent carboxylic acids include: dicarboxylic acids such as
oxalic acid, malonic acid, succinic acid, adipic acid and
diglycolic acid; tricarboxylic acids such as propanetricarboxylic
acid, and the like. However, the polyvalent carboxylic acids are
not limited to these examples. Examples of aminocarboxylic acids
include glycine, aspartic acid, and the like. However, the
aminocarboxylic acids are not limited to these examples. Among
these, polyvalent carboxylic acids are preferable, and oxalic acid,
malonic acid and succinic acid are more preferable. When the above
carboxylic acids and alkaline salts thereof are contained, a
concentration thereof in the chemical conversion treatment liquid
should preferably be in the range of 0.2 to 2 mole, should more
preferably be in the range of 0.3 to 2 mole, should still more
preferably be in the range of 0.5 to 2 mole, and should still
further more preferably be in the range of 0.7 to 1.8 mole per mole
of trivalent chromium ions.
[0053] In addition, the chemical conversion treatment liquid may
contain one or more kinds of ions of metal selected from Mg, Al,
Mn, Ti, W, V, Mo, Ni, Fe, Zn, Zr, Ca, Nb, Ta, Sn and Ce. When the
metal ions are contained, a concentration thereof in the chemical
conversion treatment liquid should preferably be 1 to 10 g/l, and
should more preferably be 2 to 8 g/l.
[0054] A pH of the chemical conversion treatment liquid should
preferably be 0.5 to 5, and should more preferably be 2 to 3. The
pH may be adjusted to this range by using the inorganic acid ions
as described below, or by using an alkaline agent such as an
alkaline hydroxide, ammonia water, or the like.
[0055] The rest of the chemical conversion treatment liquid other
than the above essential components is water.
[0056] A method for forming a trivalent chromium chemical
conversion coating film on zinc or zinc alloy plating by using the
chemical conversion treatment liquid is commonly to immerse a zinc
or zinc alloy plated substrate into the chemical conversion
treatment liquid. A temperature of the chemical conversion
treatment liquid at immersion is, for example, 10 to 70.degree. C.
The temperature should preferably be 25 to 35.degree. C. An
immersion time should preferably be 5 to 600 seconds, and should
more preferably be 15 to 120 seconds. Meanwhile, immersion into a
diluted nitric acid solution, a diluted sulfuric acid solution, a
diluted hydrochloric acid solution, a diluted hydrofluoric acid
solution, or the like may be performed before trivalent chromium
chemical conversion treatment, for activating the surface of the
zinc or zinc alloy plating. The conditions and treatment operations
other than those described above may follow the conventional
hexavalent chromate treatment method.
[0057] Overcoating the trivalent chromium chemical conversion
coating film formed by using the chemical conversion treatment
liquid according to the present invention can improve the corrosion
resistance thereof, and thus is a highly effective means for
achieving longer-lasting corrosion resistance. For example, the
trivalent chromium chemical conversion coating film is firstly
formed on the zinc or zinc alloy plating using the chemical
conversion treatment liquid according to the present invention,
then washed with water, then immersed into an overcoating solution
or subjected to an electrolytic treatment therein, and thereafter
dried. Alternatively, the trivalent chromium chemical conversion
coating film may be dried after formation thereof, and thereafter
further immersed into an overcoating solution or subjected to an
electrolytic treatment therein, and then dried. Here, as the
overcoating, as well as an inorganic coating film made of
silicates, phosphates, or the like, an organic coating film made of
polyethylene, polyvinyl chloride, polystyrene, polypropylene,
methacrylate resin, polycarbonate, polyamide, polyacetal, fluorine
resin, urea resin, phenolic resin, unsaturated polyester resin,
polyurethane, alkyd resin, epoxy resin, melamine resin, or the like
may be effectively used.
[0058] As the overcoating solution for overcoating such a film,
DIPCOAT W or CC445 available from Dipsol Chemicals Co., Ltd. or the
like may be used. The thickness of the overcoating may be any
value, but should preferably be 0.1 to 30 .mu.m.
[0059] Next, the present invention is described by referring to
Examples and Comparative Examples.
EXAMPLES
Examples 1 to 8
[0060] An M6 bolt (material: iron), which had been plated with zinc
using a zincate (NZ-200 available from Dipsol Chemicals Co., Ltd.)
in Examples 1 to 2 and 6 to 8 or acidic zinc (EZ-960 available from
Dipsol Chemicals Co., Ltd.) in Examples 3 to 5 in a thickness of 8
.mu.m, was immersed in a chemical conversion treatment liquid shown
in Table 1 under conditions shown in Table 1. In addition, in
Examples 6 to 8, the immersed bolt was immersed in a finishing
liquid shown in Table 1 under conditions shown in Table 1. After
immersion, the coating film was dried under conditions at
80.degree. C. for 10 minutes.
TABLE-US-00001 TABLE 1 Example 1 2 3 4 5 6 7 8 Composition of
trivalent chromium chemical conversion treatment liquid Cr.sup.3-
(mol/l) 0.077 0.077 0.077 0.077 0.077 0.077 0.077 0.077 Cr.sup.6+ 0
0 0 0 0 0 0 0 Oxalic acid (g/l) 12 12 12 12 12 12 12 12 (mol/mol of
Cr.sup.3+) (1.7) (1.7) (1.7) (1.7) (1.7) (1.7) (1.7) (1.7)
Co.sup.2+ (mol/l) 0.034 0.034 0.034 0.034 0.034 0.034 0.034 0.034
hexavalent chromium generation Tannic Gallic Thiourea Vanadium ion
phosphate ion -- -- -- suppressing agent (0.5 g/l) acid acid
(vanadium (sodium chloride) dihydrogen phosphate) Nitrogen content
in terms of 4.2 4.2 4.2 4.2 4.2 4.2 4.2 4.2 nitrogen atoms (g/l) pH
2.3 2.3 2.3 2.3 2.3 2.3 2.3 2.3 Treatment temperature (.degree. C.)
30 30 30 30 30 30 30 30 Treatment time (seconds) 40 40 40 40 40 40
40 40 Composition of finishing liquid Ascorbic acid (g/l) 2 Tannic
acid (g/l) 1 Chromium phosphate (g/l) + 2 + 3 citric acid (g/l) pH
of finishing liquid 4 4 6 Finishing treatment 25 40 25 temperature
(.degree. C.) Finishing treatment 15 5 15 time (seconds)
[0061] A 40% chromium nitrate aqueous solution was employed as a
source of Cr.sup.3+, and cobalt nitrate was employed as a source of
Co.sup.2+. The rest of the solution was water.
Comparative Example 1
[0062] An M6 bolt (material: iron), which had been plated with zinc
using a zincate (NZ-200 available from Dipsol Chemicals Co., Ltd.)
in a thickness of 8 .mu.m, was subjected to a hexavalent chromate
treatment. As the hexavalent chromate treatment liquid, Z-493 (10
ml/l) available from Dipsol Chemicals Co., Ltd. was used, and the
bolt was immersed at 25.degree. C. for 20 seconds. After immersion,
the coating film was dried under conditions at 60.degree. C. for 10
minutes.
Comparative Example 2
[0063] A trivalent chromium chemical conversion coating film was
formed on an M6 bolt (material: iron), which had been plated with
zinc using a zincate (NZ-200 available from Dipsol Chemicals Co.,
Ltd.) in a thickness of 8 um. As the chemical conversion treatment
liquid, a chemical conversion treatment liquid having the following
composition was used, and the bolt was immersed at 30.degree. C.
for 40 seconds. After immersion, the coating film was dried under
conditions at 80.degree. C. for 10 minutes.
TABLE-US-00002 Cr.sup.3+ 4 g/l (40% chromium nitrate was used.
0.077 mol/l in terms of Cr) Oxalic acid 12 g/l Co(NO.sub.3).sub.2
10 g/l (0.034 mol/l in terms of Co) pH 2.3
[0064] Table 2 shows concentrations of Cr.sup.3+, concentrations of
Cr.sup.6+ and concentrations of Co.sup.2+ in the chemical
conversion coating films obtained in Examples 1 to 8 and
Comparative Examples 1 and 2, appearances, results of salt spray
test (JIS Z-2371) and amounts of hexavalent chromium eluted after
the storage test. As shown in Table 3, the coating films of
Examples 1 to 8 exhibited corrosion resistance equal to or better
than that of the conventional hexavalent chromate chemical
conversion coating film of Comparative Example 1. In addition, the
amounts of hexavalent chromium eluted after storage test were less
than the measurement limit value.
TABLE-US-00003 TABLE 2 Corrosion resistance Amount of Concentration
in Time required for Cr.sup.6+ eluted coating film (.mu.g/cm.sup.2)
Appearance of the formation of after shelf Cr.sup.3+ Cr.sup.6+
Co.sup.2+ coating film white rust (Hrs) test (.mu.g/cm.sup.2)
Example 1 8.5 0 0.7 Pale reddish green 300 <0.05 Example 2 10.5
0 2.5 Pale reddish green 300 <0.05 Example 3 6.7 0 1.6 Pale
reddish green 300 <0.05 Example 4 7.0 0 0.6 Pale reddish green
300 <0.05 Example 5 5.4 0 0.4 Pale reddish green 300 <0.05
Example 6 10.0 0 2.3 Pale reddish green 300 <0.05 Example 7 10.8
0 1.0 Pale reddish green 300 <0.05 Example 8 10.7 0 2.9 Pale
reddish green 300 <0.05 Comparative 20 6.8 0 Reddish green 240
6.8 Example 1 Comparative 11 0.01 2.8 Pale reddish green 240 0.12
Example 2
Examples 9 to 11
[0065] An M6 Bolt (material: iron), which had been plated with zinc
using a zincate (NZ-200 available from Dipsol Chemicals Co., Ltd.)
in a thickness of 8 .mu.m, were immersed into a chemical conversion
treatment liquid shown in Table 3 under conditions shown in Table
3. After immersion, the coating film was dried under conditions at
80.degree. C. for 10 minutes.
TABLE-US-00004 TABLE 3 Example 9 10 11 Cr.sup.3+ (mol/l) 0.038
0.038 0.038 Cr.sup.6+ (ppm) 0 0 0 Nitrogen content in terms of 90
90 90 nitrogen atoms (ppm) SO.sub.4.sup.2- (g/L) 0 6.0 6.0 Cl.sup.-
(g/L) 4.4 0 0 Thiodiglycolic acid (g/L) 2 (430) 2 (430) 0 (in terms
of sulfur content (ppm)) Thiourea (g/L) 0 0 2 (840) (in terms of
sulfur content (ppm)) Co.sup.2+ (ppm) 200 200 200 Si (g/L) 2 2 2 ph
of treatment liquid 2.4 2.4 2.4 Treatment temperature (.degree. C.)
30 30 30 Treatment time (seconds) 60 40 40
[0066] A 35% chromium chloride aqueous solution (Example 9) or a
35% chromium sulfate aqueous solution (Examples 10 and 11) was
employed as a source of Cr.sup.3+. Cobalt chloride (Example 9) or
cobalt sulfate (Examples 10 and 11) was employed as a source of
Co.sup.2+. Si was an acidic colloidal silica (SNOWTEX-O available
from Nissan Chemical Industries, Ltd.). The rest of the solution
was water.
Examples 12 to 14
[0067] Overcoating was performed on the trivalent chromium chemical
conversion coating film of Example 9. Table 4 shows the overcoating
conditions.
TABLE-US-00005 TABLE 4 Example 12 13 14 Type of Chromium Inorganic
Methacrylate overcoating phosphate-based silicate-based resin-based
inorganic inorganic Si-dispersed-type coating film coating film
organic coating film Treatment 150 ml/l 200 ml/l Undiluted liquid
concentration was used Treatment 45.degree. C., 25.degree. C.,
25.degree. C., conditions 10 seconds 30 seconds 30 seconds Name of
agent ZTB-118 CC-445Y DIPCOAT W available from available from
available from Dipsol Chemicals Dipsol Chemicals Dipsol Chemicals
Co., Ltd. Co., Ltd. Co., Ltd.
[0068] Table 5 shows concentrations of Cr.sup.3+, concentrations of
Cr.sup.6+ and concentrations of Co.sup.2+ in the chemical
conversion coating films obtained in Examples 9 to 14 and
Comparative Examples 1 and 2, appearances, results of salt spray
test (JIS Z-2371) and amounts of hexavalent chromium eluted after
storage test. As shown in Table 5, the coating films of Examples 9
to 14 exhibited corrosion resistance equal to or better than that
of the conventional hexavalent chromate chemical conversion coating
film of Comparative Example 1. In addition, the overcoated coating
films (Examples 12 to 14) exhibited better corrosion resistance
than the conventional hexavalent chromate chemical conversion
coating film. In addition, the amounts of hexavalent chromium
eluted after storage test were less than the measurement limit
value.
TABLE-US-00006 TABLE 5 Corrosion resistance Amount of Concentration
in Time required for Cr.sup.6 + eluted coating film
(.mu.g/cm.sup.2) Appearance of the formation of after shelf
Cr.sup.3+ Cr.sup.6+ Co.sup.2+ coating film white rust (Hrs) test
(.mu.g/cm.sup.2) Example 9 7.0 0 0.1 Light blue 240 <0.05
Example 10 5.8 0 0.1 Light blue 240 <0.05 Example 11 6.0 0 0.1
Light blue 240 <0.05 Example 12 7.0 0 0.1 light interference
1000 or more <0.05 color Example 13 7.0 0 0.1 colorless 1000 or
more <0.05 Example 14 7.0 0 0.1 colorless 1000 or more <0.05
Comparative 20 6.8 0 Reddish green 240 6.8 Example 1 Comparative 11
0.11 2.8 Pale reddish green 240 0.12 Example 2
(Measurement of Cr.sup.6+ Concentration in Coating Film)
[0069] A coating film sample (50 cm.sup.2) was immersed into
approximately 50 ml of hot water at a temperature of 100.degree. C.
for 10 minutes. An amount of hexavalent chromium eluted from the
coating film sample was determined by the absorption spectroscopy
using diphenylcarbazide (in accordance with EN-15205).
(Measurement of Cr.sup.3+ Concentration and Co.sup.2+ Concentration
in Coating Film)
[0070] After measuring the Cr.sup.6+ concentration, the same sample
was dissolved into hydrochloric acid, and Cr.sup.3+ and Co.sup.2+
concentrations in the solution was measured by ICP optical emission
spectrometry.
(Salt Spray Test)
[0071] In a salt spray test, evaluation was made in accordance with
JIS-Z-2371.
(Procedure of Storage Test and Measurement of Amount of Hexavalent
Chromium Eluted after the Storage Test)
[0072] A storage test was performed as an acceleration test by
employing a method in which a sample for the elution test was left
for 30 days in a constant temperature and humidity chamber
maintained at a temperature of 80.degree. C. and a humidity of 95%.
Then, the sample after the storage test was immersed into hot water
at a temperature of 100.degree. C. for 10 minutes by a method
similar to the above-described measuring method of Cr.sup.6+
concentration in a coating film. An amount of hexavalent chromium
eluted from the coating film sample was determined by absorption
spectroscopy using diphenylcarbazide (in accordance with
EN-15205).
Examples 15 to 20
[0073] An M6 Bolt (material: iron), which had been plated with zinc
using a zincate (NZ-200 available from Dipsol Chemicals Co., Ltd.)
in a thickness of 8 .mu.m, was immersed into a chemical conversion
treatment liquid shown in Table 6 under conditions shown in Table
6. After immersion, the coating film was dried under conditions at
80.degree. C. for 10 minutes.
TABLE-US-00007 TABLE 6 Example 15 16 17 18 19 20 Cr.sup.3+ (mol/l)
0.038 0.038 0.038 0.038 0.038 0.038 Cr.sup.6+ (ppm) 0 0 0 0 0 0
Nitrogen content in 135 270 270 90 90 90 terms of nitrogen atoms
(ppm) Tartaric acid (g/l) 0 0 0 2 (0.35) 2 (0.35) 0 (mol/mol of
Cr.sup.3+) Malic acid(g/l) 5 (0.97) 5 (0.97) 0 0 0 5 (0.97)
(mol/mol of Cr.sup.3+) SO.sub.4.sup.2- (g/l) 0 0 2 2 0 0 Cl.sup.-
(g/l) 4 4 4 4 4 4 Co.sup.2+ (mol/l) 0.015 0.008 0 0.008 0.008 0.008
VOSO.sub.4 (g/l) 1 1 0 0 1 0 Ti(SO.sub.4).sub.2 0 0 1 0 0 1
MgSO.sub.4 (g/l) 0 0 0 2 0 0 Si (g/l) 5 2 5 10 5 10 ph of treatment
2.0 2.1 2.0 2.3 2.4 2.5 liquid Treatment temperature 40 40 30 30 30
30 (.degree. C.) Treatment time 20 30 60 40 40 60 (seconds)
[0074] A 35% chromium chloride aqueous solution was employed as a
source of Cr.sup.3+. Cobalt chloride was employed as a source of
Co.sup.2+. Si was an acidic colloidal silica (SNOWTEX-O available
from Nissan Chemical Industries, Ltd.). The rest of the solution
was water. Note that, the nitrogen content was derived from
NO.sub.3.sup.-.
TABLE-US-00008 TABLE 7 Corrosion resistance Amount of Concentration
in Time required for Cr.sup.6+ eluted coating film (.mu.g/cm.sup.2)
Appearance of the formation of after shelf Cr.sup.3+ Cr.sup.6+
Co.sup.2+ coating film white rust (Hrs) test (.mu.g/cm.sup.2)
Example 15 7.2 0 0.15 Light blue 240 <0.05 Example 16 7.0 0 0.1
Light blue 240 <0.05 Example 17 6.2 0 0 Light blue 168 <0.05
Example 18 5.0 0 0.15 Light blue 144 <0.05 Example 19 4.3 0 0.1
Light blue 144 <0.05 Example 20 4.0 0 0.1 Light blue 144
<0.05
* * * * *