Note: Descriptions are shown in the official language in which they were submitted.
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Aqueous Surface Conditioner and SurFace Conditioning Method for
Phosphating Treatment
Background of the Invention
Field of the Invention
The present invention relates to an aqueous surface conditioner for use in a
phosphate coating treatment performed on the surface of a metal material such
as a
sheet of iron, steel, zinc-plated steel, or aluminum in order to promote the
chemical
conversion reaction and shorten the duration thereof and to achieve greater
fineness
of the crystals that make up the phosphate coating. The invention also relates
to a
method for the surface conditioning of a metal material.
Discussion of the Related Art
The formation of fine and closely-spaced phosphate coating crystals on a
metal surface has become necessary today in order to improve corrosion
resistance
IO after painting in the phosphating treatments peuformed on automobiles and
to extend
the life of pressing molds or reduce fiiction during pressing in phosphating
treatments used for plastic working. In view of this, a surface conditioning
step is
carried out prior to a phosphate coating chemical conversion step for the
purpose of
activating the metal surface so that fine and closely-spaced phosphate coating
crystals will be obtained and creating nuclei for the deposition of phosphate
coating
crystals. The following is a typical example of a phosphate coating chemical
conversion process performed in order to obtain fine and closely-spaced
phosphate
coating crystals.
(1) degreasing
(?) multi-stage water rinsing
(3) surface conditioning
(4) phosphate coating chemical conversion treatment
(5) mufti-stage water rinsing
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(6) pure water rinsing
Surface conditioning is performed in order to make phosphate coating
crystals finer and more closely-spaced. Compositions with this aim have been
discussed in U.S. Patents 2,874,081, 2,322,349, and 2,310,239, for example,
and
examples of the main constituent components of the surface conditioner include
titanium, pyrophosphoric acid ions, orthophosphoric acid ions, and sodium
ions.
The above-mentioned surface conditioning compositions are called "Jernstedt
salts,"
and titanium ions and titanium colloids are included in aqueous solutions
thereof. A
metal that has been degreased and rinsed with water is immersed in an aqueous
solution of one of the above-mentioned surface conditioning compositions, or a
phosphating treatment surface conditioner is sprayed onto the metal, causing
the
titanium colloid to be adsorbed to the metal surface. The adsorbed titanium
colloid
forms the nuclei for phosphate coating crystal precipitation in the subsequent
phosphate coating chemical conversion step, which promotes the chemical
conversion reaction and makes the phosphate coating crystals finer and more
closely-spaced. All of the surface conditioning compositions in industrial use
today
make use of Jernstedt salts. Various problems have been encountered, however,
when a titanium colloid obtained from a Jernstedt salt is used in a sunace
conditioning process.
The first of these problems is that the phosphating treatment surface
conditioner deteriorates over time. When a conventional surface conditioning
composition is used, this composition is extremely effective in terms of
malting the
phosphate coating crystals finer more closely-spaced immediately after an
aqueous
solution is produced. However, the titanium colloid agglomerates a few days
after
the aqueous solution is prepared. The phosphating treatment surface
conditioner
loses its effect within this time regardless of whether it has been used or
not, and the
phosphate coating crystals that are obtained end up being coarse.
Japanese Laid-Open Patent Application S63-76883 proposes a method for
measuring the average particle diameter of the titanium colloid in a
phosphating
treatment surface conditioner, continuously discarding the phosphating
treatment
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surface conditioner so that the average particle diameter will be less than a
specified
value, and supplying fresh surface conditioning composition in an amount
corresponding to the discarded amount, thereby maintaining the surface
conditioning
effect at a constant level. However, while this method does allow the effect
of the
phosphating treatment surface conditioner to be maintained quantitatively, the
phosphating treatment surface conditioner has to be discarded for the effect
to be
maintained. Also, a large quantity of phosphating treatment surface
conditioner
must be discarded with this method in order to keep the effect of the
phosphating
treatment surface conditioner at the same level as when the aqueous solution
was
first produced. Therefore, in actual practice, the wastewater treatment
capacity of
the plant where this method is used also comes into question, so the effect is
maintained through a combination of continuous discarding and complete
replacement of the phosphating treatment surface conditioner.
The second problem is that the effect and service life of a phosphating
treatment surface conditioner are greatly affected by the hardness of the
water used
during replenishment. Industrial water is usually used for replenishing a
phosphating treatment surface conditioner. As is commonly known, though,
industrial water contains calcium, magnesium, and other such cationic
components
that are the source of the total hardness, although the amounts contained can
vary
greatly depending on the source of the industrial water. It is known that the
titanium
colloid that is the main component of a conventional phosphating treatment
surface
conditioner takes on an anionic charge in an aqueous solution, and the
electrical
repulsion thereof disperses the colloid and keeps it from settling. Therefore,
if
cationic components such as calcium or magnesium are present in large quantity
in
industrial water, the titanium colloid will be electrically neutralized by the
cationic
components, the repulsive force will be lost, agglomeration and settling will
occur,
and the effect of the colloid will be lost.
In view of this, a method has been proposed in which a condensed phosphate
such as a pyrophosphate is added to a phosphating treatment surface
conditioner for
the purpose of sequestering the cationic components and maintaining the
stability of
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the titanium colloid. Unfortunately, when a large quantity of condensed
phosphate is
added to a phosphating treatment surface conditioner, the condensed phosphoric
acid
reacts with the surface of a steel sheet and forms an inert film, which
results in poor
chemical conversion in the subsequent phosphate coating chemical conversion
process. Also, in locales where the calcium or magnesium content is extremely
high,
purified water must be used for supplying and replenishing the phosphating
treatment surface conditioner, which is a major drawback in terms of cost.
The third problem is that the temperature and pH are limited in their range.
Specifically, if the temperature is over 35°C and the pH is outside a
range of 8.0 to
9.5, the titanium colloid will agglomerate and lose its surface conditioning
effect.
Therefore, the predetermined temperature and pH range must be used with a
conventional surface conditioning composition, and the surface conditioning
composition cannot be added to a degreasing agent or the like so that the
effect of
cleaning and activating a metal surface will be obtained with a single liquid
over an
extended period of time.
The fourth problem is that there is a limit to how fine phosphate coating
crystals can be made through the effect of a phosphating treatment surface
conditioner. The surface conditioning effect is obtained by causing the
titanium
colloid to adsorb to a metal surface and form the nuclei during phosphate
coating
crystal precipitation. Therefore, the more titanium colloid particles are
adsorbed to
the metal surface in the surface conditioning step, the finer and more closely-
spaced
the resulting phosphate coating crystals will be. The most obvious way to
achieve
this would be increase the number of titanium colloid particles in the
phosphating
treatment surface conditioner, that is, raise the titanium colloid
concentration. When
the concentration is increased, however, there is an increase in the frequency
of
collision between the titanium colloid particles in the phosphating treatment
surface
conditioner, and these collisions cause the titanium colloid to agglomerate
and settle.
The upper limit to the concentration of titanium colloids currently being used
is 100
ppm or less (as titanium in the phosphating treatment surface conditioner),
and it has
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been impossible to make phosphate coating crystals finer by increasing the
titanium
colloid concentration over this level.
In view of this, Japanese Laid-Open Patent Applications S56-156778 and
S57-23066 disclose a surface conditioning method in which a suspension
containing
an insoluble phosphate of a divalent or trivalent metal is sprayed under
pressure onto
the surface of a steel strip as a surface conditioner other than a Jernstedt
salt. With
this surface conditioning method, however, the effect is only realized when
the
suspension is sprayed under pressure onto the target material, so this method
cannot
be used for surface conditioning in a phosphate coating chemical conversion
treatment performed by ordinary dipping or spraying.
Japanese Patent Publication S40-1095 discloses a surface conditioning
method in which a zinc plated steel sheet is dipped in a high-concentration
suspension of an insoluble phosphate of a divalent or trivalent metal. The
examples
given for this method, however, are limited to a zinc plated steel sheet, and
obtaining
a surface conditioning effect requires the use of a high-concentration
insoluble
phosphate suspension of no less than 30 g/L.
Therefore, even though various problems associated with Jernstedt salts have
been indicated, so far no one has proposed a new technique to replace them.
Also, because the mechanism by which these salts act is not clear, it is
uncertain on which substances these salts will have a surface conditioning
effect, and
searching for these substances entailed a tremendous amount of labor.
Summary of the Invention
It is an object of the present invention to solve the above-mentioned
problems and provide a novel phosphating treatment surface conditioner that
has
excellent stability over time and is used to promote the chemical conversion
reaction
and shorten the duration thereof in a phosphate coating chemical conversion
treatment, and to reduce the size of the resulting phosphate coating crystals.
The inventors examined means for solving the above problems, and closely
studied the mechanism by which surface conditioners function. This led to the
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discovery that in the course of producing a phosphate coating, the coating
components reach a state of supersaturation as the metal dissolves. The most
important effect of a surface conditioner is that the crystals it produces
function as
nuclei for phosphate coating crystals. The performance of a surface
conditioner is
determined by how effectively it can act as crystal nuclei. In other words,
the
inventors found that crystals with a lattice constant close to that of
phosphate coating
crystals function as pseudo-crystal nuclei, resulting in a surface
conditioning effect.
Further research in this area led to the peufection of the present invention.
Specifically, the present invention relates to an aqueous suuace conditioner
for use in a phosphating treatment, which contains crystals having an average
diameter of 5 ~m or less in an amount of at least 0.1 g/L, said crystals
having a two-
dimensional epitaxy that matches within 3% of misfit with the crystal lattice
of one
phosphate coating selected from among (1) hopeite (Zn3(PO~)~ ~ 4H~0) and/or
phosphophyllite (Zn~Fe(POø)~ ~ 4H~0), (2) scholzite (CaZn~(P04)Z ~ 2H~0), and
(3)
hureaulite (Mns(P04)~[P03(OH)]2 ~ 4H~Oj.
Brief Description of the Drawings
Fig. 1 is a concept diagram in which a LaMer diagram is applied to a surface
conditioner (crystal growth steps);
Fig. 2 shows the unit crystal lattices for hopeite (zinc phosphate) and
magnesium hydrogenphosphate; and
Fig. 3 is a diagram in which unit crystal lattices of hopeite have been
arranged, with the grid-shaped solid line portion being a view of these
crystal lattices
viewed perpendicular to the (020) plane, and the dashed line portion being the
unit
crystal lattices of magnesium hydrogenphosphate arranged over these.
Detailed Description of the Invention
In terms of how they are produced, phosphate coating crystals can be
described by a LaMer diagram that shows the process in which crystals
precipitate
from a solution as a result of increased concentration. In general, as the
solute
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concentration rises, crystal precipitation will not occur as soon as the
saturation
concentration is exceeded, and crystal production occurs only when the crystal
nucleus production concentration C*",;~ is reached, after which the crystals
grow, so
the solute concentration decreases. Phosphate coating crystals are believed to
precipitate through the same process, and this corresponds to when no surface
conditioner is used (corresponds to the solid line portion in Fig. 1). In this
case,
crystal nuclei are produced only in the shaded area in Fig. 1. Because there
are few
crystal nuclei, the crystal coating is often coarse, and it takes a long time
for the
coating production reaction to conclude.
In contrast, when a surface conditioner is used, because the titanium colloid
particles or the like that constitute this component function as pseudo-nuclei
for the
phosphate coating crystals, crystal growth already begins at a concentration
C*x that
is lower than the crystal nucleus production concentration C*~";". In this
case, the
number of crystal nuclei is determined by the number of titanium colloid
particles or
the like contained in the surface conditioner, so closely-spaced coating
crystals can
be produced by increasing the number of these particles. As shown in Fig. 1,
the
coating crystals are produced in a short time, so the phosphate chemical
conversion
treatment does not take as long. Here, the closer the concentration C*X at
which
crystal growth commences on the pseudo-crystal nuclei is to the saturation
concentration CS, the less time it will take to produce the coating, so
efficiency is
higher.
Because of all this, substances capable of become pseudo-crystal nuclei in a
surface conditioner were closely examined.
As a result, it was confirmed that when the phosphate coating is comprised
mainly of hopeite and/or phosphophyllite, a surface conditioning effect will
be
observed with crystals of magnesium hydrogen phosphate (MgHPOd ~ 3H~0),
zirconium oxide (ZrOz), zinc oxalate (Zn(COO)~), cobalt oxalate (Co(COO)~),
iron
orthosilicate (FeZSi04), iron metasilicate (FeSi03), and magnesium borate
(Mg3(B03)2); when the phosphate coating is comprised mainly of scholzite, this
effect will be observed with crystals of anhydrous cobalt phosphate
(Co3(P04)~),
anhydrous zinc phosphate ('y-Zn3(P04)~), anhydrous zinc magnesium phosphate
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(Zn~Mg(P04)~), anhydrous zinc cobalt phosphate (~-Zn~Co(PO~)~), and anhydrous
zinc iron phosphate ('y-Zn2Fe(P04)2); and when the phosphate coating is
comprised
mainly of hureaulite, this effect will be observed with crystals of calcium
orthosilicate (Ca~SiOø ~ HBO), calcium metaphosphate (Ca3(P03)~ ~ lOH~O), and
manganese(II) metaphosphate (Mn3(P03)~ ~ lOH~O). The term "mainly" as used
above means that the hopeite and/or phosphophyllite; scholzite; or hureaulite
accounts for at least 50 mass%, and preferably at least 70 mass%, of the
phosphate
coating. These surface conditioning substances can be used singly or in
combinations of two or more types according to the corresponding phosphate
coating.
The inventors turned their attention to the lattice constant of the crystals
of
these surface conditioning substances, and found it to be close to the lattice
constant
of the phosphate coating crystals. If the crystal structures are similar, this
means that
these substances will be effective as pseudo-crystal nuclei; this is Known as
epitaxy.
Manmade rain is often given as an example of epitaxy. When a micropowder
of silver bromide is scattered in water vapor that is supersaturated and
supercooled,
the silver bromide becomes the nuclei for the growth of ice crystals,
resulting in rain.
This phenomenon occurs because the lattice constant of the silver bromide
crystals is
extremely close to the lattice constant of ice, and the growth on one type of
crystal of
a different type of crystal with a similar lattice constant is known in the
semiconductor field as epitaxial growth.
The inventors noted a surface conditioning effect in many different
substances, and as a result learned that, as mentioned above, a substance that
has a
surface conditioning effect on a phosphate coating is a substance whose
epitaxy
closely matches that of the phosphate coating crystals.
The matching of epitaxy will now be discussed in detail.
Fig. 2 shows the unit lattice of hopeite (Zn~(P04)~ ~ 4H~0). The grid-shaped
solid line portion in Fig. 3 is a view of these crystal lattices arranged and
viewed
perpendicular to the (020) plane. The dashed line portion in Fig. 3
illustrates the unit
lattices of magnesium hydrogenphosphate (MgHP04 ~ 3H~0) arranged over these,
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and the lattices match up well. Actually, zinc phosphate is deposited over
magnesium hydrogenphosphate, and as long as there is a good match between the
lattices as above, the crystals will seat well and grow readily. There is a
certain
amount of lattice misalignment in this example as well, and this is called
misfit. In
this example, the a axis of the zinc phosphate versus the b axis of the
magnesium
0
hydrogenphosphate is 10.6845/10.6067 A = 1.0073, so the misfit is 0.7%.
Similarly,
the c axis of the magnesium hydrogenphosphate versus double the c axis of the
zinc
phosphate is 10.0129/(5.0284 x 2) = 0.9956, so the misfit is -0.4%.
Naturally, the smaller the misfit, the better the match between the crystal
lattices. What should be noted here is that the integer multiples of one
lattice
constant may also match another, and all plane combinations must be taleen
into
account.
If we thus calculate the misfit in a two-dimensional plane for all plane
combinations, we find that substances with a surface conditioning effect all
have a
two-dimensional misfit within 3%.
Table 1 is an example of calculating the misfit for the above-mentioned
surface conditioning substances used when a zinc phosphate coating is hopeite
and/or phosphophyllite (Zn2Fe(P04)~ ~ 4H20). The two-dimensional misfit was
within 3% in every case, and a surface conditioning effect was observed.
Furthermore, no surface conditioning effect was observed with substances in
which the misfit was over 3%.
It is known that a zinc phosphate coating contains not only hopeite but also a
large amount of phosphophyllite. Phosphophyllite has a crystal structure that
is
extremely similar to that of hopeite, and the crystal lattices are also very
close, so the
two precipitate as mixed crystals.
The above description of epitaxy was for when a zinc phosphate coating is
produced, but the same applies to when the coating produced is scholzite or
hureaulite. The misfit should be calculated by taking into account all
possible
arrangement combinations of the crystal lattice of scholzite or hureaulite
instead of
the crystal lattice of the zinc phosphate shown in Fig. 2.
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Table 2 is an example of calculating the misfit for the above-mentioned
surface conditioning substances used when a zinc phosphate coating is
scholzite.
The two-dimensional misfit was within 3% in every case, and a suuface
conditioning
effect was observed when a scholzite coating was produced.
Table 3 is an example of calculating the misfit for the above-mentioned
surface conditioning substances used when a zinc phosphate coating is
hureaulite.
The two-dimensional misfit was within 3% in every case, and a surface
conditioning
effect was observed when hureaulite was produced.
It is preferable for the two-dimensional misfit to be within 2.5%, whether
with (1) hopeite and/or phosphophyllite, (2) scholzite, or (3) hureaulite.
The average diameter of the crystals of these surface conditioning substances
must be no more than 5 pm, and 1 pm or less is preferable. The surface
conditioning effect will be weak if the average diameter is over 5 ~ m.
There are no particular restrictions on the concentration of these crystals in
the surface conditioner of the present invention, but the crystals must be
contained in
an amount of at least 0.1 g/L, with 0.1 to 50 g/L being preferable, and 1 to 5
g/L
being even better. The surface conditioning effect will be inadequate if the
amount
is less than 0.1 g/L, but no further effect will be obtained by exceeding 50
g/L, so
this would merely be a waste of money.
Another essential component of the surface conditioner of the present
invention is water. This water may be purified water, tap water, or industrial
water.
The above-mentioned surface conditioning substances are usually suspended in
water. If needed, a dispersant may be used to suspend the substances.
A monosaccharide, oligosaccharide, polysaccharide, etherified
monosaccharide, etherified oligosaccharide, etherified polysaccharide, water-
soluble
macromolecular compound, or the like can be used as a dispersant. Examples of
monosaccharides include glucose, fructose, mannose, galactose, and ribose;
examples of oligosaccharides include sucrose, maltose, lactose, trehalose, and
maltotriose; examples of polysaccharides include starch, dextrin, dextran, and
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glycogen; examples of etherified monosaccharides, oligosaccharides, and
polysaccharides include compounds obtained by etherifying the hydroxyl groups
of
the constituent monosaccharides with substituents such as -NO~, -CH3, -C,H~OH,
-CH~CH(OH)CH3, and -CH~COOH; and examples of water-soluble
macromolecular compounds include polyvinyl acetate, partially hydrolyzed
polyvinyl acetate, polyvinyl alcohol, polyvinyl alcohol derivatives (such as
cyanoethylated acrylonitrile, acetalated formaldehyde, urethanated urea, and
derivatives in which carboxyl groups, sulfone groups, amide groups, or the
like have
been introduced), and copolymers of vinyl acetate with copolymerizable
monomers
(such as acrylic acid, crotonic acid, and malefic anhydride).
There are no particular restrictions on the concentration of the dispersant as
long as the amount is sufficient to disperse the crystals used in the present
invention,
but the concentration is usually 1 to 2000 ppm.
The material to be conditioned with the surface conditioner of the present
invention is any metal material that will undergo a phosphate chemical
conversion
treatment, examples of which include steel, zinc and zinc plated materials,
materials
plated with zinc alloys, aluminum and aluminum plated materials, and
magnesium.
The surface conditioner of the present invention is usually applied after the
metal material has been degreased and rinsed with water, but this is not
necessarily
the case. The surface conditioning perfoumed with the surface conditioner of
the
present invention is performed by bringing this conditioner into contact with
the
surface of a metal material for at least 1 second. More specifically and
preferably,
the metal material is either immersed in the conditioner for about 10 seconds
to 2
minutes, or the conditioner is sprayed onto the metal material for about 10
seconds
to 2 minutes. This treatment is ordinarily carried out with the surface
conditioner at
normal ambient temperature (i.e., about 15°C to about 30°C), but
can be carried out
at anywhere between normal temperature and about 80°C. Any of a great
number of
substances can be selected with the present invention as dictated by the
intended
application, so it is also possible to disperse these crystals in a degreasing
agent, and
perform the degreasing and surface conditioning at the same time. In this case
the
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treatment is usually performed by immersion or spraying for about 1 to 3
minutes at
50 to 80°C.
Examples
Next, examples and comparative examples will be used to describe in detail
the effect of applying the phosphating treatment surface conditioner of the
present
invention. A zinc phosphate-based treatment for automobiles is given as an
example
of a phosphating treatment, but the applications of the aqueous surface
conditioner
for use in a phosphating treatment pertaining to the present invention are not
limited
to this example. All instances of "%" below indicate mass%.
Test sheets
The abbreviations for an descriptions of the test sheets used in the examples
and comparative examples are given below.
SPC: cold rolled steel sheet, JIS G 3141
EG: double-sided electrogalvanized steel sheet, plating basis weight: 20 g/m~
Al: aluminum sheet, JIS 5052
Alkali degreasing solution
FAINCLEANA I~460 (registered trademark of Nihon Parkerizing Co., Ltd.)
was diluted to 2% with tap water and used in both the examples and the
comparative
examples.
Zinc phosphate treatment solution
PALBOND L3020 (registered trademark of Nihon Parkerizing Co., Ltd.) was
diluted with tap water, adjusted to a component concentration of 4.8%, 23
point total
acidity, 0.9 point free acidity, and 3 point accelerator, and used in both the
examples
and the comparative examples (these concentrations are commonly used today in
automotive zinc phosphate treatments).
The overall treatment process will now be discussed.
Treatment steps
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(1) alkali degreasing, 42°C, spraying for 120 seconds
(2) water rinsing, room temperature, spraying for 30 seconds
(3) surface conditioning, room temperature, immersion for 20 seconds
(4) zinc phosphate treatment, 42°C, immersion for 120 seconds
(5) water rinsing, room temperature, spraying for 30 seconds
(6) deionized water rinsing, room temperature, spraying for 30 seconds
Surface conditioner
The method for preparing the phosphating treatment surface conditioner used
in the examples will now be discussed.
Example 1
A magnesium hydrogenphosphate (MgHPOa ~ 3H~0) reagent was pulverized
for 60 minutes in a ball mill using zirconia beads, and this product was used
as a
crystal powder whose epitaxy matched within 3%. This powder was suspended in
purified water and then filtered through a 5 pm paper filter. The magnesium
hydrogenphosphate concentration was adjusted to 5 g/L, and this product was
used
as a surface conditioner.
Example 2
A zinc oxalate dihydrate (Zn(COO)z ~ 2H20) reagent was baked for 1 hour at
200°C and then analyzed with an X-ray analyzer, which confirmed it to
be zinc
oxalate (Zn(COO)2). This was pulverized for 60 minutes in a ball mill using
zirconia beads, and this product was used as a crystal powder whose epitaxy
matched within 3°Io. This powder was suspended in purified water and
then filtered
through a 5 ~m paper filter. The zinc oxalate concentration was adjusted to 5
g/L,
and this product was used as a surface conditioner
Example 3
A cobalt oxalate dihydrate (Co(COO)~ ~ 2H~0) reagent was baked for 1 hour
at 200°C and then analyzed with an X-ray analyzer, which confirmed it
to be cobalt
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oxalate (Co(COO)~). This was pulverized for 60 minutes in a ball mill using
zirconia beads, and this product was used as a crystal powder whose epitaxy
matched within 3%. This powder was suspended in purified water and then
filtered
through a 5 pm paper filter. The cobalt oxalate concentration was adjusted to
5 g/L,
and this product was used as a surface conditioner.
Example 4
12.3 g of a boric acid (H3B03) reagent and 12.1 g of a magnesium oxide
(Mg0) reagent were ground together in a mortar and then baked for 1 hour at
1000°C. This product was analyzed with an X-ray analyzer, which
confirmed it to
be magnesium borate (Mg3(B03)2). Unreacted boron oxide (B~03) and magnesium
oxide (Mg0) were detected as impurities in this product. This was pulverized
for 60
minutes in a ball mill using zirconia beads, and this product was used as a
crystal
powder whose epitaxy matched within 3%. This powder was suspended in purified
water and then filtered through a 5 ~m paper filter. The magnesium borate
concentration was adjusted to 5 g/L, and this product was used as a surface
conditioner.
Example 5
10 g of zirconia sol NZS-30B made by Nissan Chemical Industries, Ltd. (a
suspension containing 30% zirconium oxide fines with a diameter of 70 nm) was
diluted to
1 L and used as a crystal material whose epitaxy matched within 3 %. The
product
adjusted in this manner was used as a surface conditioner.
Comparative Example 1
A silicon dioxide (Si02) reagent was pulverized for 60 minutes in a ball mill
using zirconia beads, and this product was used as a crystal powder. This
powder
was suspended in purified water and then filtered through a 5 ~m paper filter.
The
silicon dioxide concentration was adjusted to 5 g/L, and this product was used
as a
surface conditioner.
Comparative Example 2
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A magnesium oxide (Mg0) reagent was pulverized for 60 minutes in a ball
mill using zirconia beads, and this product was used as a crystal powder. This
powder was suspended in purified water and then filtered through a 5 ~tm paper
filter. The magnesium oxide concentration was adjusted to 5 giL, and this
product
was used as a surface conditioner.
Comparative Example 3
This is an example of not using a surface conditioner. Specifically, the
surface conditioning (3) was omitted from the above-mentioned treatment steps.
Painting and evaluation steps
In the examples and the comparative examples, each test sheet that had
undergone the above-mentioned zinc phosphate treatment steps (1) to (6) was
painted with a cationic electrodeposition paint (ELECRON 2000, made by Kansai
Paint) in a film thickness of 20 ~tm. This was halted for 25 minutes at
180°C, after
which an intermediate coat (automotive-use intermediate coat made by Kansai
Paint)
was applied such that the intermediate coat thickness would be 40 Vim, and
this was
baked for 30 minutes at 140°C. Each test sheet that had been given an
intermediate
coat was then given a top coat (automotive-use top coat made by Kansai Paint)
in a
top coat thickness of 40 ~tm, which was then halted for 30 minutes at
140°C. The
triple-coated sheet with a total film thickness of 100 ~m thus obtained was
subjected
to a saltwater spray test.
Method for evaluating zinc phosphate coating
(1) Appearance
Each sheet was examined visually and checked for unevenness or thin paint
in the zinc phosphate coating. The evaluation was given as follows.
o uniformly good appearance
o some unevenness
o unevenness and thin paint present
x severe thin paint
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(2) Coating weight (CW)
The mass of the treated sheet after the chemical conversion was measured
(referred to as W1 (g)), then the chemical conversion treated sheet was
subjected to a
coating removal treatment with the stripper and stripping conditions given
below,
the mass of this product was measured (referred to as W2 (g)), and the coating
weight was calculated using Formula I.
With a cold rolled steel sheet
stripper: 5% chromic acid aqueous solution
stripping conditions: 75°C, 15 min., immersion stripping
With a galvanized sheet
stripper: ammonium dichromate (2 mass%) + 28% aqueous
ammonia (49 mass%) + pure water (49 mass%)
Coating mass (g/m') _ (W1 - W2)/0.021 Formula (I)
Method for evaluatin~paint film
The paint film was evaluated by the method given below in both the
examples and the comparative examples.
(1) Saltwater spray test (JIS Z 2371)
An electropainted sheet in which cross-cuts had been made was sprayed for
960 hours with 5% saltwater. Upon completion of the spraying, the maximum
width
that peeled from the cross-cuts on one side was measured, and an evaluation
was
made.
Table 4 shows the characteristics of a chemical conversion coating obtained
in a zinc phosphate treatment using the various phosphating treatment-use
aqueous
surface conditioners of the examples and comp~uative examples, and shows the
results of a performance evaluation conducted after painting. A dash (-) in
Table 4
means that the coating mass was not measured because the coating was not
deposited properly.
16
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It was confirmed from the results in Table 4 that the phosphating treatment
aqueous surface conditioners whose epitaxy was within 3%, which were the
products
of the present invention, had a surface conditioning effect.
On the other hand, calculation of the epitaxy for SiOZ and hopeite
(Comparative Example 1) revealed the misfit to be SiOz (a)/hopeite (c) _
4.9732/5.0284 = 0.989, and SiO~ (c)/hopeite (a) = 6.9236/10.6067 = 0.653, so
the
misfit was -1.1% and-34.7%.
Similarly, in Comparative Example 2, Mg0 (a)/hopeite (c) = 4.213/5.0284 =
0.838, and Mg0 (a) x 2/hopeite (a) = 8.426/10.6067 = 0.794, so the misfit was
-16.2% and -20.6%. (Mg0 is a cubic crystal, so only the a axis was used.)
Thus, it was confirmed that there was no surface conditioning effect with the
comparative examples, in which the misfit was large and the epitaxy was
different.
17
CA 02434306 2003-07-09
WO 02/061176 PCT/US02/00273
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