U.S. patent application number 11/412186 was filed with the patent office on 2006-11-02 for electrolytic phosphating process.
This patent application is currently assigned to DENSO Corporation. Invention is credited to Shigeki Matsuda.
Application Number | 20060243600 11/412186 |
Document ID | / |
Family ID | 37233383 |
Filed Date | 2006-11-02 |
United States Patent
Application |
20060243600 |
Kind Code |
A1 |
Matsuda; Shigeki |
November 2, 2006 |
Electrolytic phosphating process
Abstract
This invention provides a phosphating process that can form a
film suitable for a cold forging foundation within 60 seconds and
preferably 30 seconds or less. The process uses a treatment bath
that is formed of a phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in
phosphoric acid, contains phosphoric acid (H.sub.3PO.sub.4),
phosphate ions, zinc ions and nitrate ions, may contain at least
one kind of metal ion selected from the group consisting of nickel
ions, cobalt ions, copper ions, manganese ions and iron ions, and
further contains 0.5 g/l or below of metal ions other than the film
forming components. The process involves electrolytic treatment by
applying a voltage between a metal as a positive electrode and a
treated article as a negative electrode and forms a phosphate film
on the surface of the treated article. The phosphate ion solution
prepared by dissolving zinc in phosphoric acid
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) is a solution obtained by
dissolving 8 parts by mass to a maximum dissolution concentration
of zinc in 100 parts by mass of phosphoric acid.
Inventors: |
Matsuda; Shigeki;
(Okazaki-city, JP) |
Correspondence
Address: |
HARNESS, DICKEY & PIERCE, P.L.C.
P.O. BOX 828
BLOOMFIELD HILLS
MI
48303
US
|
Assignee: |
DENSO Corporation
Kariya-city
JP
|
Family ID: |
37233383 |
Appl. No.: |
11/412186 |
Filed: |
April 26, 2006 |
Current U.S.
Class: |
205/318 |
Current CPC
Class: |
C25D 9/04 20130101 |
Class at
Publication: |
205/318 |
International
Class: |
C25D 9/04 20060101
C25D009/04 |
Foreign Application Data
Date |
Code |
Application Number |
Apr 28, 2005 |
JP |
2005-131600 |
Claims
1. An electrolytic phosphating process using a treatment bath that
is formed of a phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in
phosphoric acid, contains phosphoric acid (H.sub.3PO.sub.4),
phosphate ions, zinc ions and nitrate ions, may contain at least
one kind of metal ion selected from the group consisting of nickel
ions, cobalt ions, copper ions, manganese ions and iron ions, and
further contains 0.5 g/l or below of metal ions other than said
film forming components, said process comprising the step of
conducting an electrolytic treatment by applying a voltage between
a metal as a positive electrode and a treated article as a negative
electrode and forming a phosphate film on the surface of the
treated article.
2. An electrolytic phosphating process according to claim 1,
wherein said electrolytic treatment is carried out by using a
treatment bath the pH of which is adjusted to 1.5 to 2.5 and the
ORP (oxidation-reduction potential) of which is kept at 90 to 450
mV (silver/silver chloride electrode potential).
3. An electrolytic phosphating process according to claim 1, which
contains at least 15 g/l of phosphoric acid and phosphate ions, at
least 15 g/l of zinc ions, at least 12.5 g/l of nitrate ions, and 0
to 3 g/l of at least one kind of metal ion selected from the group
consisting of nickel ions, cobalt ions, copper ions, manganese ions
and iron ions.
4. An electrolytic phosphating process according to claim 1,
wherein said positive electrode is selected from zinc or iron.
5. An electrolytic phosphating process according to any of claim 1,
wherein, after anodic electrolysis is carried out by using said
treated article as the positive electrode and zinc or iron as the
negative electrode, cathodic electrolysis is carried out by using
said treated article as the negative electrode and zinc or iron as
the positive electrode.
6. An electrolytic phosphating process according to claim 1,
wherein a voltage of not greater than 6 V is applied by connection
to a D.C. power source.
7. An electrolytic phosphating process according to claim 1,
wherein said phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) dissolving zinc in phosphoric
acid is a solution prepared by dissolving 8 parts by mass to a
maximum dissolution concentration of zinc in 100 parts by mass of
phosphoric acid.
8. An electrolytic phosphating process according to claim 1,
wherein said phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in
phosphoric acid, is a solution prepared by dissolving 15 to 25
parts by mass of zinc in 100 parts by mass of phosphoric acid.
9. An electrolytic phosphating process according to claim 1,
wherein said phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in
phosphoric acid, is a solution prepared by dissolving zinc oxide,
zinc hydroxide or metallic zinc in a phosphate ion solution.
10. An electrolytic phosphating process according to claim 1,
wherein a ratio of the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) and phosphoric acid
(H.sub.3PO.sub.4) in said electrolytic treatment bath has a ratio
of 0.4 to 1 represented by the relation [phosphate ion solution in
which zinc is dissolved
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+)]/[phosphate ion solution in which
zinc is dissolved (H.sub.2PO.sub.4.sup.-+Zn.sup.2+)+phosphoric acid
(H.sub.3PO.sub.4)].
11. An electrolytic phosphating process according to claim 1,
wherein said electrolytic treatment bath contains the phosphate ion
solution (H.sub.2PO.sub.4.sup.-+Zn.sup.2+) dissolving zinc in
phosphoric acid, phosphoric acid (H.sub.3PO.sub.4) and zinc
nitrate, and may contain a metal nitrate constituted by at least
one kind of nitrate selected from the group of nickel nitrate,
cobalt nitrate, copper nitrate and manganese nitrate.
12. An electrolytic phosphating process according to claim 1,
wherein the electrolytic treatment is carried out at a cathodic
electrolysis current density of 1 to 18 A/dm.sup.2 to form a
phosphate film on the surface of the treated article.
13. An electrolytic phosphating process according to claim 1,
wherein the electrolytic treatment is carried out under a condition
free of any obstacles, that may impede the flow of a current
between the positive electrode and the negative electrode, to form
a phosphate film on the surface of the treated article.
14. An electrolytic phosphating process according to claim 1,
wherein a zinc phosphate film is formed by setting the electrolytic
treatment time to 60 seconds or less.
15. An electrolytic phosphating process according to claim 1,
wherein two or more kinds of voltages and currents are applied to
one treated article, depending on positions thereof, by using two
or more power sources and electrodes.
Description
BACKGROUND OF THE INVENTION
[0001] 1. Field of the Invention
[0002] This invention relates to an electrolytic phosphating
process for forming a phosphate film, mainly composed of zinc
phosphate, on a surface of a treated article. More specifically,
the invention relates to a process for forming a film on a surface
of a metal material having electric conductivity.
[0003] 2. Description of the Related Art
[0004] A phosphating process is a treatment technology that is
utilized for coating a foundation treatment of steel materials, a
cold-forging lubrication treatment, and so forth. The phosphating
process that is predominant at present is a non-electrolytic
process but a variety of electrolytic phosphating processes have
been examined in order to conduct a more efficient phosphating
process.
[0005] Japanese Unexamined Patent Publication (Kokai) No.
2000-234200, for example, describes a prior art of such an
electrolytic phosphating process and describes a basic method of
using electrodes and a power source when the electrolytic
phosphating process is executed. The reference mentions the
dissociation state of acids in relation to a treatment bath and
describes that the bath does not contain acids having a greater
dissociation (nitric acid, for example) than phosphoric acid.
[0006] Furthermore, Japanese Unexamined Patent Publication (Kokai)
No. 2002-322593 describes measures necessary for continuously
carrying out the electrolytic phosphating process and describes
also that intermediate products such as a N.sub.2O.sub.4 gas formed
during the intermediate reaction process must be removed. However,
these prior art technologies require a treatment time of 2 minutes
or more and have not acquired methods for further shortening the
electrolytic phosphating process for processed articles which have
complicated shapes.
[0007] On the other hand, an electrolytic process has been
employed, in the past, for steel wires and shortening of the
process time has also been studied. Japanese Unexamined Patent
Publication (Kokai) No. 2000-80497 discloses a novel method, and a
novel apparatus, for forming a phosphate film having a higher
performance as a lubrication foundation, on steel wires of low
carbon steel, high carbon steel and low alloy steel, more quickly
than the prior art and without generating any sludge. In this
reference, the wire material shown in FIG. 1 is sequentially
processed in each step. This mode of processing is peculiar to a
wire material. The a material has a constant rod-like shape and its
shape is advantageous for surface-electrolyzation. The object of
the lubrication treatment (phosphate film) is drawing of the steel
wire material (processed from large wire diameter to small wire
diameter) and is limited plastic working. This object is basically
different from the object of the present invention, that is, cold
forging of the treated articles as components having complicated
shapes including convex and concave shapes and requiring high
machining precision, and cannot be applied to such articles.
[0008] It can be appreciated, on the other hand, that Japanese
Patent No. 3,479,609 is directed to preventing sludge and to
speeding-up the treatment, and presumably can be applied to the
machining of components because the Examples use test panels and
not wire materials. However, because nitric acid (HNO.sub.3) is
added to the treatment bath in this reference, the treatment bath
is a bath that uses acids having a higher degree of dissociation
than phosphoric acid. The reference further describes that the
cover ratio of the film is 50% and this is not sufficient when a
cathodic electrolytic process is carried out for 10 seconds in a
treating solution composed only of phosphoric acid, nitric acid and
zinc carbonate. Sodium nitrite, etc, is added to the bath so as to
achieve a 100% cover ratio. In other words, this reference requires
an additive containing soluble ions that do not precipitate as the
phosphate film in order to promote film formation.
SUMMARY OF THE INVENTION
[0009] Because an electrolytic phosphating process supplies
electrolytic energy (current/voltage) by directly connecting a
treated article to an external D.C. power source, the efficiency of
the electrolytic reaction is more satisfactory than the
non-electrolytic process of the prior art. Therefore, this process
can shorten the treatment time (electrolytic time) in comparison
with the non-electrolytic system of the prior art.
[0010] The time required for the phosphating process is generally
120 seconds for processing the coating foundation and 5 to 10
minutes for processing the foundation for cold forging in the
non-electrolytic system according to the prior art.
[0011] The cold forging foundation requires a larger film thickness
than the coating foundation and the treatment time becomes longer,
too. Therefore, cold forging foundation requires shortening of the
treatment time. An object of the invention is to provide a
phosphating process capable of forming a film suitable for cold
forging within a short time of 60 seconds or less and preferably 30
seconds or less. When the treatment time can be shortened, the size
of treatment equipment can be reduced and a dedicated machine can
be constituted. Such a reduction is effective for a smaller
installation area, a transfer line construction, reduction of
intermediate stocks, saving man-power and energy, and so forth, and
these are the objects to be accomplished in practical utilization
of component machining.
[0012] A system for forming a film containing a phosphate by
electrolysis from a treatment bath (solution) is described in
Japanese Unexamined Patent Publication (Kokai) No. 2000-234200
described above. The present invention uses the system of this
reference as the basis and forms a film mainly composed of zinc
phosphate (crystal) by further developing this system.
[0013] To accomplish the object described above, the present
invention provides the following inventions.
[0014] (1) An electrolytic phosphating process using a treatment
bath that is formed of a phosphate ion solution made by dissolving
zinc in phosphoric acid, contains phosphoric acid, phosphate ions,
zinc ions and nitrate ions, may contain at least one kind of metal
ion selected from the group consisting of nickel ions, cobalt ions,
copper ions, manganese ions and iron ions and, further, contains
0.5 g/l or less of metal ions other than the film forming
components, the method comprising the step of conducting an
electrolytic treatment by applying a voltage between the metal as a
positive electrode and a treated article as a negative electrode
and forming a phosphate film on the surface of the treated
article.
[0015] (2) The electrolytic phosphating process as described in
(1), wherein the electrolytic treatment is carried out by using a
treatment bath the pH of which is adjusted to 1.5 to 2.5 and the
ORP (oxidation-reduction potential) of which is kept at 90 to 450
mV (silver/silver chloride electrode potential).
[0016] (3) The electrolytic phosphating process as described in (1)
or (2), in which the bath contains at least 15 g/l of phosphoric
acid and phosphate ions, at least 15 g/l of zinc ions, at least
12.5 g/l of nitrate ions, and 0 to 3 g/l of at least one kind of
metal ion selected from the group consisting of nickel ions, cobalt
ions, copper ions, manganese ions and iron ions.
[0017] (4) The electrolytic phosphating process as described in any
of (1) through (3), wherein the positive electrode is selected from
zinc or iron.
[0018] (5) The electrolytic phosphating process as described in any
of (1) through (4), wherein, after anodic electrolysis is carried
out by using the treated article as the positive electrode and zinc
or iron as the negative electrode, cathodic electrolysis is carried
out by using the treated article as the negative electrode and zinc
or iron as the positive electrode.
[0019] (6) The electrolytic phosphating process as described in any
of (1) through (5), wherein a voltage of not greater than 6 V is
applied through connection to a D.C. power source.
[0020] (7) The electrolytic phosphating process as described in any
of (1) through (6), wherein the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in a
phosphate ion solution, is a solution prepared by dissolving 8
parts by mass to a maximum dissolution concentration of zinc in 100
parts by mass of phosphoric acid.
[0021] (8) The electrolytic phosphating process as described in any
of (1) through (7), wherein the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), made by dissolving zinc in a
phosphate ion solution, is a solution prepared by dissolving 15 to
25 parts by mass of zinc in 100 parts by mass of phosphoric
acid.
[0022] (9) The electrolytic phosphating process as described in any
of (1) through (8), wherein the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) dissolving zinc in a phosphate
ion solution is a solution prepared by dissolving zinc oxide, zinc
hydroxide or metallic zinc in a phosphate ion solution.
[0023] (10) An electrolytic phosphating process as described in any
of (1) through (9), wherein a ratio of the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) and phosphoric acid
(H.sub.3PO.sub.4) in the electrolytic treatment bath has a ratio of
0.4 to 1 represented by the relation [phosphate ion solution in
which zinc is dissolved
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+)]/[phosphate ion solution in which
zinc is dissolved (H.sub.2PO.sub.4.sup.-+Zn.sup.2+)+phosphoric acid
(H.sub.3PO.sub.4)].
[0024] (11) The electrolytic phosphating process as described in
any of (1) through (10), wherein the electrolytic treatment bath
contains the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+) dissolving zinc in a phosphate
ion solution, phosphoric acid (H.sub.3PO.sub.4) and zinc nitrate,
and may contain a metal nitrate constituted by at least one kind of
nitrate selected from the group consisting of nickel nitrate,
cobalt nitrate, copper nitrate and manganese nitrate.
[0025] (12) The electrolytic phosphating process as described in
any of (1) through (11), wherein the electrolytic treatment is
carried out at a cathodic electrolysis current density of 1 to 18
A/dm.sup.2 to form a phosphate film on the surface of the treated
article.
[0026] (13) The electrolytic phosphating process as described in
any of (1) through (12), wherein the electrolytic treatment is
carried out under conditions free of any obstacles that may impede
the flow of a current between the positive electrode and the
negative electrode to form a phosphate film on the surface of the
treated article.
[0027] (14) The electrolytic phosphating process as described in
any of (1) through (13), wherein a zinc phosphate film is formed by
setting the electrolytic treatment time to 60 seconds or below.
[0028] (15) The electrolytic phosphating process as defined in any
of (1) through (14), wherein two or more kinds of voltages and
currents are applied to one treated article depending on the
position thereof by using two or more power sources and
electrodes.
[0029] The present invention can shorten the phosphating treatment
time of components as treated articles. Shortening of the treatment
time allows a small installation area and in-line (transfer line)
construction. In other words, because a large phosphating treatment
apparatus according to the prior art is installed independently of
previous and subsequent process steps, components are stored before
and after the treatment apparatus. However, because the size can be
reduced, the phosphating treatment apparatus can be installed
adjacent to the previous and subsequent installation steps. In
consequence, storage of the components before and after the
phosphating treatment apparatus can be eliminated and man-power
required for transportation and storage can be omitted.
[0030] The present invention allows a decrease in the size of the
installation and lowering of the temperature and thus reduces the
use amount of energy for heating, etc. Because the invention does
not invite unnecessary reactions, the invention can prevent the
formation of by-products (sludge) and reduces the amount of
chemicals used.
[0031] The effect of the invention contributes to an improvement in
the resulting film. This is obvious from the comparison of the
films of later-appearing Examples 7 and 8 with the film of
later-appearing Comparative Example 4. In Examples 7 and 8, fine
zinc phosphate crystals are formed uniformly on the surface but a
film of large crystals are coarsely formed in Comparative Example
4. This difference in the surface conditions reflects the
difference of the deposition amounts of lubrication effective
components. In other words, a uniform zinc phosphate crystal is
advantageous for the formation of the lubrication effective
components and is hence effective for cold forgeability.
BRIEF DESCRIPTION OF THE DRAWINGS
[0032] FIG. 1 is a schematic view of a basic phosphating process
system according to the present invention;
[0033] FIG. 2 shows the formation state of films in the Examples
and the Comparative Examples;
[0034] FIG. 3 shows the formation state of films in the Examples
and the Comparative Examples;
[0035] FIG. 4 shows a current that flows when a 3 V voltage is
applied between a zinc electrode and a test piece in cathodic
electrolysis;
[0036] FIG. 5 shows a shape of a component used in Examples 7 and 8
and in Comparative Example 4, wherein formation processing is to
change the shape from the one shown in FIG. 5 to a structure shown
in FIG. 6;
[0037] FIG. 6 shows a gear-like structure of the component shown in
FIG. 5 after cold forging press;
[0038] FIG. 7 is an appearance view of a phosphate film formed in
Example 7;
[0039] FIG. 8 is an appearance view of a phosphate film formed in
Example 8;
[0040] FIG. 9 is an appearance view of a phosphate film formed in
Comparative Example 4; and
[0041] FIG. 10 shows a component B (tubular component having a
cylindrical hollow portion) used for the phosphating process in
Example 12.
DESCRIPTION OF THE PREFERRED EMBODIMENTS
[0042] In an electrolytic phosphating process according to the
invention, a treatment bath is prepared by using a phosphate ion
solution (H.sub.2PO.sub.4.sup.-+Zn.sub.2.sup.+) made by dissolving
zinc in phosphoric acid. This solution contains phosphoric acid
(H.sub.3PO.sub.4) and phosphate ions, zinc ions and nitrate ions,
and may further contain at least one kind of metal ion selected
from the group consisting of nickel ions, cobalt ions, copper ions,
manganese ions and iron ions. The content of metal ions other than
the film forming components are not greater than 0.5 g/l. The
phosphate film is formed on the surface of the treated article by
conducting electrolytic treatment by using a metal as the positive
electrode and the treated article as the negative electrode and
applying a voltage.
[0043] For example, the electrolytic treatment bath according to
the invention appropriately contains the phosphate ion solution
dissolving zinc in phosphoric acid
(H.sub.2PO.sub.4.sup.-+Zn.sub.2.sup.+), phosphoric acid
(H.sub.3PO.sub.4) and zinc nitrate, and metal nitrates constituted
by at least one kind of metal selected from nickel, cobalt, copper
and manganese. As for iron, iron is preferably supplied from the
solution made by dissolving iron in phosphoric acid in the same way
as zinc. Iron nitrate is not desirable because it exists in the
form of ferric salts (Fe.sup.3+), (Fe(NO.sub.3).sub.3), and forms
sludge.
[0044] Sodium and potassium are examples of metal ions other than
the film forming components and the treatment bath according to the
invention does not substantially contain these metal ions (not
greater than 0.5 g/l).
[0045] The main constituent elements that constitute the
electrolytic phosphating process system are "treatment bath" and
"electrolytic method". The electrolytic phosphating process
according to the invention is accomplished by examining in detail
the "treatment bath" and the "electrolytic method" in order to
shorten the film formation time in the electrolytic phosphating
process.
[0046] i) Examination of "Treatment Bath"-1:
[0047] Control of Dissociation Conditions of Phosphoric Acid
[0048] Precipitation of zinc phosphate is a phenomenon (reaction)
in which phosphoric acid enters the dissociation state as
represented by
H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-.fwdarw.PO.sub.4.sup.3-,
couples with zinc ions (Zn.sup.2+) and forms zinc phosphate
(Zn.sub.3(PO.sub.4).sub.2). In this reaction process
H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-.fwdarw.PO.sub.4.sup.3-,
acidity becomes higher towards the left side in the solution state
but the phosphate compounds (crystal:solid) is formed towards the
right side, or the solution becomes alkaline. The formation of zinc
phosphate in the film form by the electrolytic process is to
electrolyze the solution containing phosphoric acid, phosphate ions
and zinc ions in the solution state, to promote dissociation of
phosphoric acid (namely, as represented by
H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-.fwdarw.PO.sub.4.sup.3-),
and to cause the zinc phosphate crystal (Zn.sub.3(PO.sub.4).sub.2)
to precipitate as the film on the surface of the treated article.
Therefore, the phosphating treatment bath must be in the solution
state and dissociation of phosphoric acid must be limited to the
range of H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-.
[0049] The electrolytic treatment bath is preferably transparent.
To facilitate precipitation of the phosphate, the dissociation
state of phosphoric acid must be promoted in the treatment bath.
The dissociation state of phosphoric acid can be promoted by
dissolving zinc oxide (ZnO), zinc hydroxide (Zn(OH).sub.2) or
metallic zinc (Zn) in the H.sub.3PO.sub.4 solution. In other words,
dissociation of phosphoric acid can be promoted and controlled by
the following reaction formulas.
2H.sub.3PO.sub.4+ZnO.fwdarw.2H.sub.2PO.sub.4.sup.-+Zn.sup.2++2H.sub.2O
(1)
2H.sub.3PO.sub.4+Zn(OH).sub.2.fwdarw.2H.sub.2PO.sub.4.sup.-+Zn.sup.2-
++2H.sub.2O (2)
2H.sub.3PO.sub.4+Zn.fwdarw.2H.sub.2PO.sub.4.sup.-+Zn.sup.2++H.sub.2
(3)
[0050] The reaction formulas (1) to (3) described above can be
carried out substantially stably in a solution dissolving from 8
parts by mass to a maximum dissolution concentration of Zn.sup.2+
in 100 parts by mass of H.sub.3PO.sub.4 in a weight ratio.
Preferably, the phosphate ion solution dissolving zinc contains 15
to 25 parts by mass of zinc in 100 parts by mass of phosphoric
acid. In the present invention, the solution dissolving from 8
parts by mass to a maximum dissolution concentration of Zn.sup.2+
in 100 parts by mass of H.sub.3PO.sub.4 may be called the "element
component consisting of H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight" for the convenience sake. In
this way, the element component composed only of "H.sub.3PO.sub.4"
and the element component composed of "H.sub.2PO.sub.4.sup.-:100
parts by weight+Zn.sup.2+:25 parts by weight" can be used in the
invention. The component "H.sub.3PO.sub.4" is the constituent
component of the prior art but "H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight" is the constituent component
that is proposed by the present invention. In other words, it is
clear that the dissociation state of the phosphoric acid ion is
different between pure "H.sub.3PO.sub.4" and
"H.sub.2PO.sub.4.sup.-:100 parts by weight+Zn.sup.2+:25 parts by
weight".
[0051] As described above, the invention uses two kinds of
components, that is, [H.sub.3PO.sub.4] and
[H.sub.2PO.sub.4.sup.-:100 parts by weight+Zn.sup.2+:25 parts by
weight] as the phosphoric acid components constituting the
phosphating treatment bath. The invention proposes a ratio
[H.sub.2PO.sub.4.sup.-:100 parts by weight+Zn.sup.2+:25 parts by
weight]/[H.sub.3PO.sub.4]+[H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight] (weight ratio) and defines it
as [zinc dissolving phosphate ion solution ratio] (also called [Zn
25% dissolving phosphate ion solution ratio]).
[0052] Therefore, the solution of [zinc dissolving phosphate ion
solution ratio]=1 means that phosphoric acid constituting the
treatment bath wholly consists of [H.sub.2PO.sub.4.sup.-:100 parts
by weight+Zn.sup.2+:25 parts by weight]. The solution of [zinc
dissolving phosphate ion solution ratio]=0.5 means that 50% of
phosphoric acid constituting the treatment bath is
[H.sub.2PO.sub.4.sup.-:100 parts by weight+Zn.sup.2+:25 parts by
weight] and the rest consists of pure [H.sub.3PO.sub.4]. The
solution of [zinc dissolving phosphate ion solution ratio]=0 means
that phosphoric acid constituting the treatment bath consists of
only pure [H.sub.3PO.sub.4].
[0053] The zinc dissolving phosphate ion solution ratio in the
electrolytic treatment bath according to the invention, that is,
[phosphate ion solution dissolving zinc in phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+)]/[phosphate ion solution
dissolving zinc in phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+)+phosphoric acid
(H.sub.3PO.sub.4)] is suitably from 0.4 to 1.
[0054] A treatment bath having a small [zinc dissolving phosphate
ion solution ratio] is a treatment bath having a large pure
[H.sub.3PO.sub.4] ratio and large (dissociation) energy is
necessary in the solution to promote dehydrogenation of
H.sub.3PO.sub.4. In contrast, a treatment bath having a large [zinc
dissolving phosphate ion solution ratio] is a treatment bath having
a large [H.sub.2PO.sub.4.sup.-:100 parts by weight+Zn.sup.2+:25
parts by weight] ratio and dehydrogenation of H.sub.3PO.sub.4 can
be promoted more easily than in the former. Therefore, the latter
solution can precipitate the zinc phosphate crystal more easily and
with a smaller electrolytic energy than the former.
[0055] By the way, the dissociation condition of phosphoric acid
has also a correlation with the hydrogen ion concentration (pH) of
the treatment bath and it is most suitable to carry out the
electrolytic treatment by using a treatment bath that is kept at a
pH of 1.5 to 2.5.
[0056] ii) Examination of "Treatment Bath"-2:
[0057] Observation of Soluble Metal Ions (Iron Ions) in Phosphoric
Acid Other Than Zinc
[0058] Iron is a metal that is soluble in the phosphate ion
solution and exhibits a similar behavior to zinc, in phosphoric
acid. Iron is often the treated material, and the possibility of
dissolution from the treated material into the treatment bath
exists. Therefore, the behavior of iron ions must be
understood.
[0059] Iron dissolves in phosphoric acid only from the metallic
state. The condition is as follows.
2H.sub.3PO.sub.4+Fe.fwdarw.2H.sub.2PO.sub.4.sup.-+Fe.sup.2++H.sub.2
(4)
[0060] In the formula (4), Fe can be dissolved substantially up to
Fe.sup.2+:20 mass parts in 100 parts by mass of H.sub.3PO.sub.4 in
terms of the mass ratio.
[0061] Unlike zinc, Fe cannot be dissolved basically from the state
of the oxide and hydroxide in phosphoric acid. Therefore,
dissolution of the oxide and hydroxide of iron is affected by:
Fe.sup.2+.fwdarw.Fe.sup.3++e:0.77V (5)
[0062] The formula (5) represents also that Fe.sup.2+ is oxidized
to Fe.sup.3+. This oxidation is generally promoted by oxygen in
normal air. Under such a normal condition, iron oxide (FeO) and
iron hydroxide (Fe(OH).sub.2) are affected and oxidized by oxygen,
and exist in the forms of Fe.sub.2O.sub.3 and Fe(OH).sub.3,
respectively. Such iron oxides cannot dissolve in phosphoric
acid.
[0063] The relation of the formula (5) also affects the stability
of the phosphating treatment bath. In other words, the Fe ions have
the tendency to change from Fe.sup.2+.fwdarw.Fe.sup.3+ in the
phosphating treatment bath. However, because solubility of
Fe.sup.3+ is far smaller than that of Fe.sup.2+, large amounts of
sludge are formed in the treatment bath with this change
(Fe.sup.2+.fwdarw.Fe.sup.3+). Such a phenomenon is by no means
desirable in the phosphating treatment bath.
[0064] Therefore, in the present invention that is directed to form
a film containing zinc phosphate as the main constituent, the Fe
ions that can be contained in the phosphating treatment bath are
supplied from the solution dissolving in phosphoric acid and the
dissolution amount (concentration) is preferably limited. It is
about 3 g/l. When the concentration is higher, large amounts of
sludge are undesirably formed in the treatment bath according to
the method of the invention.
[0065] As for metals other than Fe, Mn is, for example,
Mn.sup.2+:0.5 parts by weight on the basis of H.sub.3PO.sub.4:100
parts by weight in terms of a maximum weight ratio. It is difficult
to form an Mn phosphate film at this concentration. In the present
invention, 0 to 2 g/l of metal ions of other metals that do not
dissolve in the phosphate ion solution, such as nickel, cobalt or
copper, may be contained.
[0066] iii) Examination of [Electrolytic Method]-1
[0067] Restriction and Control of Reactions Other Than Phosphoric
Acid Dissociation
[0068] The formation of the film by dissociation of phosphoric acid
is carried out by limiting the condition of phosphoric acid of the
treatment bath up to the range of
[H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-], and promoting
[H.sub.3PO.sub.4.fwdarw.H.sub.2PO.sub.4.sup.-].fwdarw.PO.sub.4.sup.3-
and dissociation by electrolysis to form the film on the surface of
articles. In other words, PO.sub.4.sup.3- and zinc ions (Zn.sup.2+)
are coupled on the surface of the negative electrode (treated
article) and the zinc phosphate (Zn.sub.3(PO.sub.4).sub.2) crystal
is formed as the film.
[0069] It is of the utmost importance that other reactions
(reaction such as electrolysis of water) are suppressed. Reaction
products other than phosphate are formed when the reactions other
than dissociation of phosphoric acid occur (with the proviso that a
controlled reaction is permitted, whenever necessary).
[0070] Dissociation of phosphoric acid can be carried out at a
voltage lower than the voltage for the electrolysis of water. More
specifically, dissociation of phosphoric acid is promoted but
electrolysis is restricted to an impressed voltage of 6 V or below
(refer to Japanese Unexamined Patent Publication (Kokai) No.
2004-52058, for details). The invention particularly employs the
treatment bath that is prepared by using the phosphate ion solution
dissolving zinc in phosphoric acid and promotes in advance
dissociation of phosphoric acid. Therefore, the invention can
easily dissociate phosphoric acid at a voltage of 6 V or below
until the coating can be precipitated.
[0071] iv) Examination of [Electrolytic Method]-2
[0072] Measure for Lowering Current Resistance at Electrode
Surface--Electrode Materials
[0073] To obtain a film within a short time by the electrolytic
process system, it is necessary to pass as much current as possible
at a voltage of 6 V or below. To pass a greater current, a) it is
necessary [to increase the surface area of the electrode when the
material is the same], and b) [to lower the current resistance at
the electrode surface]. The measure a) is clear to everyone. The
measure b) needs the selection of electrode materials that are
suitable for the present invention. In other words, it is suitable
to select zinc or iron as the electrode material for the positive
electrode. Particularly, zinc is a metal that has a large
dissolution capacity in phosphoric acid, easily dissolves at a low
voltage and makes it possible to pass a large current.
[0074] iv) Examination of [Electrolytic Method]-3:
[0075] Measure for Lowering Current Resistance of treated
article--Adjustment of Oxidation-Reduction Potential (ORP) of
Treatment Bath
[0076] Because the electrolytic processing according to the
invention is processing at a voltage (electrolytic voltage) at
which hydrolysis of electrolysis of water does not occur, the flow
of the current on the surface of the treated article must be taken
into consideration. The observation of the oxidation-reduction
potential (ORP) and dissolution of metal materials are known as a
Pourbaix diagram. Though the Pourbaix diagram is not based on
kinetics, it can be estimated that the oxidation-reduction
potential is more advantageously set to the corrosion area
(potential) than to the passive area. The metal materials assumed
by the invention are iron and steel (inclusive of alloy steel),
aluminum, copper, and so forth. These metals are corroded at an
oxidation-reduction potential of 300 to 660 mV (hydrogen standard
electrode potential). When the oxidation-reduction potential of the
treatment bath is adjusted to this range, the current resistance on
the surface of the work (treated article) can be lowered and a
large current can flow. It is thus effective to adjust the
oxidation-reduction potential of the treatment bath to 90 to 450 mV
(silver/silver chloride electrode potential) (300 to 660 mV
(hydrogen standard electrode potential)).
[0077] Preferred examples of the present invention will be
hereinafter illustrated. FIG. 1 is a schematic view of a basic
phosphating treatment system of the present invention.
[0078] The following A or B is used as the treatment bath.
[0079] A: The treatment bath uses two kinds of phosphoric acid
components constituting the phosphating treatment bath, that is,
[H.sub.3PO.sub.4] and [H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight]. The invention indicates the
dissociation state of phosphoric acid in the treatment bath and
uses a treatment bath having the dissolving phosphate ion solution
ratio represented by [H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by
weight]/[H.sub.3PO.sub.4]+[H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight] (weight ratio) within the
range of 0.4 to 1. This treatment bath does not contain the
composition in which iron is dissolved in phosphoric acid
illustrated below.
[0080] The treatment bath contains at least 15 g/l of phosphate
ions, at least 15 g/l of zinc ions, at least 12.5 g/l of nitrate
ions, 0 to 2 g/l of ions of metals selected from the group
consisting of nickel, cobalt, copper, chromium and manganese, not
greater than 3 g/l of iron ions dissolved from the treated article
and the electrode, and not greater than 0.5 g/l of dissolution ions
other than those described above.
[0081] B: The treatment bath prepared by adding the solution having
the [zinc-dissolved phosphate ion solution ratio] of 0.4 to 1 to
the solution in which iron is dissolved in advance in phosphoric
acid to a concentration not greater than 3 g/l.
[0082] The treatment bath contains at least 15 g/l of phosphate
ions, at least 15 g/l of zinc ions, at least 12.5 g/l of nitrate
ions, 0 to 2 g/l of ions of metals selected from the group
consisting of nickel, cobalt, copper and manganese, iron ions
dissolved from the treated article and the electrode, and not
greater than 0.5 g/l of dissolution ions other than those described
above.
[0083] The electrolytic process is basically executed by conducting
anodic electrolysis and then cathodic electrolysis. In other words,
after anodic electrolysis is carried out by using the treated
article as the positive electrode and zinc or iron as the negative
electrode, cathodic electrolysis is preferably carried out by using
the treated article as the negative electrode and zinc or iron as
the positive electrode. The anodic electrolysis may be omitted
depending on the case.
[0084] The anodic electrolysis is carried out by using an auxiliary
electrode as the negative electrode and the treated article as the
positive electrode. The auxiliary electrode generally uses iron.
The cathodic electrolysis is generally carried out by using a main
electrode (zinc) as the positive electrode and the treated article
as the negative electrode. The impressed voltage is preferably 6 V
or less in both kinds of electrolysis. The electrolysis process is
preferably executed by setting the cathodic electrolysis current
density within the range of 1 to 18 A/dm.sup.2 and forming the
phosphate film on the surface of the treated article. Here, the
electrolysis process is carried out under the state where no
obstacle hindering the flow of the current exists between the
positive and negative electrodes, and the phosphate film is formed
on the surface of the treated article.
[0085] In the invention, the time for the electrolytic process can
be 60 seconds or less but can be extended, depending on the
condition and purpose of the electrolytic process, without being
limited to the former time.
[0086] To form the phosphate film by the invention, it is possible
to use two or more power sources and electrodes for one treated
article, to apply two or more different voltages and currents
depending on the position of the same treated article and to form
the phosphate film on the surface of the treated article as
illustrated in later-appearing Example 12.
[0087] Preferably, the pH of the treatment bath is set to the range
of 1.5 to 2.5 and the ORP, to 90 to 450 mV (silver/silver chloride
electrode potential) (300 to 660 mV (hydrogen standard electrode
potential)).
[0088] The invention will be explained by Examples and Comparative
Examples but is in no way limited thereto.
EXAMPLES 1 TO 6 & COMPARATIVE EXAMPLES 1 TO 3
Examples in Treatment Bath Not Containing Fe Ions
[0089] Test pieces used in Examples 1 to 6 and Comparative Examples
1 to 3 are soft steel material (SPCC material: cold rolled steel
sheet) having a size of 50 mm.times.25 mm.times.1 mm (t). After
degreasing, each test piece is immersed in a titanium type
colloidal solution and the phosphating process is carried out to
form a film. The electrolytic phosphating process is carried out by
anodic treatment (7 seconds).fwdarw.cathodic treatment (23
seconds). The electrolytic processing time was 30 seconds and was
shorter than in the prior art.
[0090] Table 1 tabulates the condition under which Examples and
Comparative Examples are carried out and their results. In other
words, Table 1 tabulates the composition of the phosphating
treatment bath, the electrolytic condition, the pH (hydrogen ion
concentration) of the treatment bath, ORP (oxidation-reduction
potential), the temperature, the total acidity (index representing,
by pt. milliliters of a 0.1N caustic soda solution required for the
neutralization titration of 10 ml of the treatment bath by the 0.1N
caustic soda till coloration to red by using phenolphthalein as an
indicator) and the formation condition of the coating. The
treatment bath of Table 1 is not a solution which is allowed to
intentionally contain Fe ions.
[0091] Incidentally, the electrolytic process is a system in which
the voltage is elevated to a predetermined voltage and the current
is caused to flow between the electrode and the treated article.
The electrode materials used for the electrolytic process are
tabulated in Table 2 and are zinc and iron.
[0092] The electrolytic voltage in the invention is 6 V or less and
the maximum voltage in Examples 1 to 6 and Comparative Examples 1
to 3 is 3 V. The impressed voltage of 3 V is a voltage that
suppresses decomposition of water. TABLE-US-00001 TABLE 1
Comparative Comparative Example 1 Example 1 Example 2 Example 2
Example 3 13 23 15 14 6 treatment dissociation [phosphoric acid 0
0.5 1 0 0.67 bath index of from H.sub.3PO.sub.4(100) + composition
phosphoric Zn(25)]/[phosphoric acid acid from H.sub.3PO.sub.4(100)
+ Zn(25)] + [phosphoric acid from H.sub.3PO.sub.4] phosphoric total
phosphoric 30 30 30 30 30 acid acid concentration: g/l
concentration phosphoric acid 0 15 30 0 20 concentration from
H.sub.3PO.sub.4(100) + Zn(25): g/l phosphoric acid 30 15 0 30 10
concentration from H.sub.3PO.sub.4: g/l zinc total zinc 15 15 15 20
20 concentration concentration: g/l Zn concentration from 0 3.75
7.7 0 5 H.sub.3PO.sub.4(100) + Zn(25): g/l Zn concentration from 15
11.25 7.3 20 15 Zn nitrate: g/l nitrate ion total NO.sub.3-- 31
23.5 16 41 31 concentration concentration: g/l NO.sub.3--
concentration 30 22.5 15 40 30 from Zn nitrate: g/l NO.sub.3--
concentration 1 1 1 1 1 from Ni nitrate: g/l nickel Ni
concentration 0.5 0.5 0.5 0.5 0.5 concentration from Ni nitrate:
g/l electrolytic anodic voltage 2 2 2 2 2 condition electrolysis
current: A/work -0.2 -0.2 0.6 -0.2 -0.2 time rise for rise for rise
for rise for rise for 4 sec and 4 sec and 4 sec and 4 sec and 4 sec
and holding holding holding holding holding for 3 sec for 3 sec for
3 sec for 3 sec for 3 sec Zn: voltage 3 3 3 3 3 cathodic
electrolysis current: A/work 1.3 1.7 1.1 1.4 1.8 time rise for rise
for rise for rise for rise for 5 sec and 5 sec and 5 sec and 5 sec
and 5 sec and holding holding holding holding holding for 18 sec
for 18 sec for 18 sec for 18 sec for 18 sec current: A/dm.sup.2 5.2
6.8 4.4 5.6 7.2 iron: voltage 2 2 2 2 2 cathodic electrolysis
current: A/work -0.2 -0.2 -0.2 -0.2 -0.2 time rise for rise for
rise for rise for rise for 5 sec and 5 sec and 5 sec and 5 sec and
5 sec and holding holding holding holding holding for 18 sec for 18
sec for 18 sec for 18 sec for 18 sec treatment PH 1.48 1.59 1.97
1.51 1.67 bath ORP: mv (silver/ 425 265 262 376 450 condition
silver chloride electrode potential) temperature: .degree. C. 30-35
30-35 30-35 30-35 30-35 total acidity: pt. 70 78 84 72 76 formed
film coating ratio: % 70 100 100 100 100 film thickness: .mu.m 1.2
5 8.8 1.8 4.5 Comparative Example 4 Example 3 Example 5 Example 6
16 19 7 17 treatment dissociation [phosphoric acid 1 0 0.67 1 bath
index of from H.sub.3PO.sub.4(100) + composition phosphoric
Zn(25)]/[phosphoric acid acid from H.sub.3PO.sub.4(100) + Zn(25)] +
[phosphoric acid from H.sub.3PO.sub.4] phosphoric total phosphoric
30 30 30 30 acid acid concentration: g/l concentration phosphoric
acid 30 0 20 30 concentration from H.sub.3PO.sub.4(100) + Zn(25):
g/l phosphoric acid 0 30 10 0 concentration from H.sub.3PO.sub.4:
g/l zinc total zinc 20 30 30 30 concentration concentration: g/l Zn
concentration from 7.7 0 5 7.7 H.sub.3PO.sub.4(100) + Zn(25): g/l
Zn concentration from 12.3 30 25 22.3 Zn nitrate: g/l nitrate ion
total NO.sub.3-- 26 61 51 46 concentration concentration: g/l
NO.sub.3-- concentration 25 60 50 45 from Zn nitrate: g/l
NO.sub.3-- concentration 1 1 1 1 from Ni nitrate: g/l nickel Ni
concentration 0.5 0.5 0.5 0.5 concentration from Ni nitrate: g/l
electrolytic anodic voltage 2 2 2 2 condition electrolysis current:
A/work 0.6 -0.2 -0.2 -0.2 time rise for rise for rise for rise for
4 sec and 4 sec and 4 sec and 4 sec and holding holding holding
holding for 3 sec for 3 sec for 3 sec for 3 sec Zn: voltage 3 3 3 3
cathodic electrolysis current: A/work 1.3 3.2 1.7 2 time rise for
rise for rise for rise for 5 sec and 5 sec and 5 sec and 5 sec and
holding holding holding holding for 18 sec for 18 sec for 18 sec
for 18 sec current: A/dm.sup.2 5.2 12.8 6.8 8 iron: voltage 2 2 2 2
cathodic electrolysis current: A/work -0.2 -0.2 -0.2 -0.2 time rise
for rise for rise for rise for 5 sec and 5 sec and 5 sec and 5 sec
and holding holding holding holding for 18 sec for 18 sec for 18
sec for 18 sec treatment PH 1.97 1.39 1.66 2.02 bath ORP: mv
(silver/ 233 317 425 211 condition silver chloride electrode
potential) temperature: .degree. C. 30-35 30-35 30-35 30-35 total
acidity: pt. 80 95 84 80 formed film coating ratio: % 100 80 100
100 film thickness: .mu.m 11.8 5 5.4 12
[0093] Examples 1 and 2 and Comparative Example 1 use the same
chemical components treatment bath. The difference between the
Examples and the Comparative Example resides in the difference of
the degree of dissociation of phosphoric acid. Comparative Example
2 and Examples 3 and 4 also use the same chemical components
treatment bath composition, too, and the difference resides in the
degree of dissociation of the phosphoric acid. This also holds true
of Comparative Example 3 and Examples 5 and 6.
[0094] FIG. 2 shows the formation state of the film. The drawing
shows that the film is reliably formed within a short time of 30
seconds in an Example though the phosphate film is not always
formed reliably in a Comparative Example.
[0095] FIG. 3 shows the film formation condition in terms of the
film thickness. The film thickness is measured by using an
electromagnetic film thickness meter LE-300J, produced by K. K.
Ketto Kagaku Kenkyusho. The film formation is excellent in the
Examples though it is poor in the Comparative Example. The film
thickness is 5 .mu.m in Comparative Example 3 and this film
thickness is the thickness of the portion at which the film is
formed. In Comparative Example 3, the film is formed on only 80% of
the surface.
[0096] FIG. 4 comparatively shows the current that flows when 3
volts are applied between the zinc electrode and the test piece
during cathodic electrolysis. The diagram shows that the current
rises with the increase of the ratio of zinc to phosphoric acid.
The current density is maximal in Comparative Example 3 but the
film formation is not reliable. To reliably conduct the film
formation, it is more important to control the dissociation state
of phosphoric acid in the solution than the current density.
[0097] The result given above indicates that the process and the
treatment bath according to the invention are effective for forming
the film within a short period of 30 seconds.
EXAMPLES 7 AND 8 AND COMPARATIVE EXAMPLE 4
[0098] Examples 7 and 8 and Comparative Example 4 are cases where
actual components (material: SUJ2: high carbon chromium bearing
steel: C:1%, Cr:1.45%) are used. The component is the one that is
used for a brake system of a car, and is shaped into a gear-like
structure by a cold forging press after lubrication treatment. This
shaping process is to change the shape shown in FIG. 5 to the shape
shown in FIG. 6. Therefore, the component used in Examples 7 and 8
and Comparative Example 4 is the component shown in FIG. 5.
[0099] Comparative Example 4 represents the treatment process
according to the prior art and is a non-electrolytic system.
Examples 7 and 8 are the treatment under the same condition with
the exception of the electrolytic treatment time. Table 2 shows the
outline for executing this treatment. TABLE-US-00002 TABLE 2
Comparative Example 4 Non-electrolytic Example 7 Example 8
treatment treatment bath dissociation index [phosphoric acid from
0.43 0.43 Palbond 3684X composition of phosphoric acid
H.sub.3PO.sub.4(100) + (formation chemical Zn(25)]/ [phosphoric
acid from produced by Nippon H.sub.3PO.sub.4(100) + Parkerizing
Co., Ltd) Zn(25)] + [phosphoric acid from H.sub.3PO.sub.4)
phosphoric acid total phosphoric acid 42 42 concentration
concentration: g/l phosphoric acid concentration from 18 18
H.sub.3PO.sub.4(100) + Zn(25): g/l phosphoric acid concentration
from 24 24 H.sub.3PO.sub.4: g/l zinc total zinc concentration: g/l
22.5 22.5 concentration Zn concentration from 4.5 4.5
H.sub.3PO.sub.4(100) + Zn(25): g/l Zn concentration from 18 18 Zn
nitrate: g/l nitrate ion total NO.sub.3-- 38 38 concentration
concentration: g/l NO.sub.3-- concentration 36 36 from Zn nitrate:
g/l NO.sub.3-- concentration 2 2 from Ni nitrate: g/l nickel Ni
concentration from 1 1 concentration Ni nitrate: g/l electrolytic
anodic voltage 1.5 1.5 no electrolysis, condition electrolysis
treatment time: 600 sec current: A/work 0.2 0.2 time rise for 3 sec
rise for 4 sec and holding and holding for 2 sec for 6 sec Zn:
cathodic voltage 3 3 electrolysis current: A/work 1.4 1.4 time rise
for 3 sec rise for 4 sec and holding and holding for 7 sec for 16
sec current: A/dm.sup.2 5.2 5.2 iron: cathodic voltage 2 2
electrolysis current: A/work -0.2 -0.2 time rise for 3 sec rise for
4 sec and holding and holding for 7 sec for 16 sec treatment bath
PH 1.99 2 -- condition ORF: mv (silver/silver chloride 400 355 --
electrode potential) temperature: .degree. C. 32 32 80 total
acidity: pt. 82 82 43 promoter concentration -- -- 3 formed film
cover ratio: % 100 100 100 lubrication effective component: 4.5 4.4
1.5 deposition weight: g/m.sup.2 phosphate film: deposition 6.7 10
4 weight: g/m.sup.2 press cold forging press: machining 67 67 68
machinability load mean value: ton
[0100] FIGS. 7 to 9 show the appearances of the phosphate films
formed. FIG. 7 shows Example 7, FIG. 8 shows Example 8 and FIG. 9
shows Comparative example 4.
[0101] The treated articles are treated through the steps of
degreasing--surface adjustment.fwdarw.phosphating
treatment.fwdarw.lubrication treatment (immersion in sodium
stearate solution at 80.degree. C. for 3 min) (surface adjustment
is omitted in Comparative Example 4).
[0102] The difference between Examples and Comparative Examples is
remarkable in the actual treatment. The treatment time is 10
minutes in the Comparative Example but is 15 seconds and 30 seconds
in the Examples. The appearances of the formed films are also
remarkably different between the Examples and the Comparative
Examples. The films of the Examples are compact and the zinc
phosphate crystal is uniformly formed on the surface of the treated
article. Therefore, the foundation steel is not directly exposed.
In contrast, the phosphate film of Comparative Example (prior art)
is composed of coarse zinc phosphate crystals. Consequently,
whereas the iron surface is reliably covered with the film in the
method of the present invention, it can be observed, through an
SEM, that the foundation steel is exposed by the film in the method
of the prior art.
[0103] The lubrication (treatment) film acts on the zinc phosphate
film and is formed. Therefore, it is important as to whether the
steel surface is reliably covered with the film having the zinc
phosphate crystal or is not covered reliably. When the surface is
reliably covered with the zinc phosphate crystal, the lubrication
treatment bath (Na stearate) does not come into direct contact with
the steel surface. When the film is incomplete, however, the
lubrication treatment bath (Na stearate) comes into direct contact
with the steel surface. This impedes the operation of the
lubrication components and forms an incomplete lubrication film. In
other words, when the steel components (iron ions, etc) dissolve in
the lubrication treatment bath, the iron ions coagulate the
lubrication film (a uniform dispersion of soap) and impedes its
uniform formation. In other words, a film containing the
coagulation components is formed. The lubrication film (soap)
should be uniformly dispersed, exist in the film form and thus
operate effectively. It is therefore important to form a sufficient
zinc phosphate film and the present invention accomplishes this
object.
[0104] The difference between the Examples and the Comparative
Example reflecting the condition described above can be confirmed
from the appearance of the formed film. In the lubrication
effective component formed uniformly as the lubrication film
component shown in Table 2, the mass ratio of Example/Comparative
Example is 3/1 and the Example is greater than, and superior to,
Comparative Example. The zinc phosphate deposition amount is
different between Example 7 and Example 8 and the lubrication
effective component remains substantially at the same level. This
is presumably because the surface is reliably covered with the zinc
phosphate film as can be confirmed, through an SEM, in Examples 7
and 8.
[0105] Incidentally, the lubrication effective component tabulated
in Table 2 is measured by immersing the film in the lubrication
treatment bath (Na stearate bath) during the formation of the
lubrication film, manually removing the solid contents (solid
contents such as Na stearate separated from the film) precipitating
on the surface and measuring the components forming the uniform and
continuous film. The measurement of the film is conducted by
immersing the film in isopropyl alcohol boiling at 70.degree. C.
for 15 to 20 minutes, measuring the weights of the treated article
before and after immersion and converting them to values per unit
area (m.sup.2). This measurement method of the lubrication film
(reaction soap) is different from the prior art method that is
applied to film formation by the non-electrolytic method. The
difference in the lubrication film formation methods reflects the
fact that the non-electrolytic treatment method according to the
prior art cannot form a complete zinc phosphate film but that the
method of the present invention can form it.
[0106] The deposition amount of the zinc phosphate crystal is
important but it has been confirmed that the difference in the film
formation condition is important, too. No difference occurs in
Examples and Comparative Example as to the cold forging press load,
but it can be confirmed that the Examples are more advantageous
from the difference in the properties of the film.
[0107] As a result of X-ray diffraction, it was confirmed that the
films of Examples 7 and 8 and Comparative Example 4 contain zinc
phosphate crystals, though this is not shown in the drawings.
EXAMPLE 9 AND COMPARATIVE EXAMPLES 5 AND 6
[0108] Example 9 and Comparative Examples 5 and 6 represent the
case where the degree of dissociation of phosphoric acid is
adjusted by dissolving iron in phosphoric acid, without dissolving
zinc in phosphoric acid.
[0109] Table 3 represents the outline of the Examples. In Examples
9 and Comparative examples 5 and 6, [Zn25% dissolving phosphate ion
solution ratios] represented by [H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by
weight]/[H.sub.3PO.sub.4]+[H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight] (mass ratio) are all zero.
[Zn25% dissolving phosphate ion solution ratio]=0 is the same as in
Comparative examples 1 to 3. However, it is novel that the degree
of dissociation of phosphoric acid is regulated by dissolving iron
in phosphoric acid. TABLE-US-00003 TABLE 3 Comparative Comparative
Example 10 Example 11 Example 5 Example 6 Example 9 24 25 26 27 28
treatment bath dissociation index [phosphoric acid from 0.67 0.67 0
0 0 composition of phosphoric acid H.sub.3PO.sub.4(100) +
Zn(25)]/[phosphoric acid from H.sub.3PO.sub.4(100) + Zn(25)] +
[phosphoric acid from H.sub.3PO.sub.4] phosphoric acid total
phosphoric acid 30 30 30 30 30 concentration concentration: g/l
phosphoric acid concentration 20 20 0 0 0 from H.sub.3PO.sub.4(100)
+ Zn(25): g/l phosphoric acid ion from 10 10 30 15 15 phosphoric
acid + iron phosphoric acid concentration from 0 0 0 15 15
H.sub.3PO.sub.4: g/l zinc total zinc concentration: g/l 18 18 20 10
20 concentration Zn concentration from 5 5 0 0 0
H.sub.3PO.sub.4(100) + Zn(25): g/l Zn concentration from 13 13 20
10 20 Zn nitrate: g/l nitrate ion total NO.sub.3-- 27 27 41 21 41
concentration concentration: g/l NO.sub.3-- 26 26 40 20 40
concentration from Zn nitrate: g/l NO.sub.3-- 1 1 1 1 1
concentration from Ni nitrate: g/l nickel Ni concentration from 0.5
0.5 0.5 0.5 0.5 concentration Ni nitrate: g/l Fe Fe ion from
phosphoric 1 2 6 3 3 concentration acid + iron electrolytic anodic
voltage 2 2 2 2 2 condition electrolysis current: A/work -0.2 -0.2
0.6 0.8 1 time rise for 4 sec rise for 4 sec rise for 4 sec rise
for 4 sec rise for 4 sec and holding and holding and holding and
holding and holding for 3 sec for 3 sec for 3 sec for 3 sec for 3
sec Zn: cathodic voltage 3 3 3 3 3 electrolysis current: A/work 1.5
1.3 0.9 0.9 1.4 time rise for 5 sec rise for 5 sec rise for 5 sec
rise for 5 sec rise for 5 sec and holding and holding and holding
and holding and holding for 18 sec for 18 sec for 18 sec for 18 sec
for 18 sec current: A/dm.sup.2 6 5.2 3.6 3.6 5.6 iron: cathodic
voltage 2 2 2 2 2 electrolysis current: A/work -0.2 -0.2 -0.2 -0.2
-0.2 time rise for 5 sec rise for 5 sec rise for 5 sec rise for 5
sec rise for 5 sec and holding and holding and holding and holding
and holding for 18 sec for 18 sec for 18 sec for 18 sec for 18 sec
treatment bath PH 1.93 1.9 2.22 1.5 1.49 condition ORP: mv
(silver/silver 130 114 85 179 184 chloride electrode potential)
temperature: .degree. C. 30-35 30-35 30 30 30 total acidity: pt. 74
75 58 58 64 formed film coating ratio: % 100 100 100 70 100 film
thickness: .mu.m 6.2 5.4 5 2 3.6
[0110] Example 9 and Comparative Example 5 and 6 use a steel
material (SPCC material: cold rolled steel sheet) having a size of
50 mm.times.25 mm.times.1 mm (t) as the test piece. After being
degreased, each test piece is immersed in a titanium type colloidal
solution for the surface adjustment and is then subjected to the
phosphating process to form the film. The phosphating process is
carried out in a cycle of anodic treatment (7 sec).fwdarw.cathodic
treatment (23 sec). The electrolytic treatment time is 30 seconds
and is shorter than the prior art technology.
[0111] Comparative Examples 5 and 6 use the treatment bath that
does not use the phosphate ion solution
(H.sub.2PO.sub.4.sup.-+Zn.sup.2+), and cannot provide the effect of
film formation according to the invention.
[0112] Example 9 is the example where the film formation can be
carried out in the presence of the Fe ion but this bath generates
sludge due to the Fe ion.
EXAMPLES 10 AND 11
[0113] In Examples 10 and 11, the adjustment of the degree of
dissociation of phosphoric acid is made by using two methods, that
is, the method that dissolves iron in phosphoric acid to adjust
dissociation and the method that uses [Zn25% dissolving phosphate
ion solution ratio represented by [H.sub.2PO.sub.4.sup.-:100 parts
by weight+Zn.sup.2+:25 parts by
weight]/[H.sub.3PO.sub.4]+[H.sub.2PO.sub.4.sup.-:100 parts by
weight+Zn.sup.2+:25 parts by weight] (mass ratio). Both examples 10
and 11 can form a film.
[0114] The remarkable difference between Examples 1 to 8 that do
not use the Fe ion for the dissociation adjustment of phosphoric
acid and Examples 9 to 11 that use the Fe ion for dissociation
adjustment resides in the oxidation-reduction potential (ORP) of
the treatment bath. The ORP is higher than 200 mV (silver-silver
chloride electrode potential) in all the former (bath not using Fe)
while it is lower than 200 mV in the latter (bath using Fe). This
indicates that the dissolved Fe ion greatly affects the ORP of the
solution (lowers the ORP). To adjust the ORP of the treatment bath,
therefore, it is possible to use a [solution adjusting the degree
of dissociation of phosphoric acid by dissolving a small amount of
iron in phosphoric acid].
EXAMPLE 12
[0115] The component B shown in FIG. 10 is a tubular component
having a cylindrical hollow portion. When the electrolytic
treatment is conducted for such a component, a flow of the current
to the pipe inner diameter portion drops and film formation at that
portion is restricted. In Example 12, an auxiliary electrode
different from the main electrode is inserted into the hollow
portion and an electrolytic treatment system separate from the main
electrolytic treatment circuit is formed by using the auxiliary
power source different from the main power source to conduct the
electrolytic treatment. The solid matter of the metal ions (metal
material) described in claims 1 and 7 can be used for the electrode
material of the auxiliary electrode.
[0116] The film can be reliably formed on the pipe inner diameter
portion by using such an auxiliary electrode.
[0117] The present invention can shorten the phosphating treatment
time of a component, as a treated article, and can improve the
performance of the resulting film. The reduction of the treatment
time makes it possible to produce a dedicated treatment machine and
to reduce its size, and to reduce the installation area for the
equipment and to convert it to an in-line (transfer line)
equipment. The obtained uniform zinc phosphate crystals are
particularly effective for cold-forging machining.
* * * * *