Note: Descriptions are shown in the official language in which they were submitted.
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The present invention relates to a method of treatiny
steel sheets, whereby the steel sheets are coated with the
solution containing at least one water-so:Luble or water-dispersible
lithium silicate which is a mixture of silicic acid or silicate
and lithium salt, e.g. lithlum hydroxide, said solution further ~ -
containing a water-soluble or water-dispersible saturated or un-
saturated fatty acid compound, higher alcohol wax, polyethylene ~ -
resin, fluorine resin or silicate resin. Furthermore, the solu-
tion can contain at least one water-soluble chromic acid. chrom-
ate, dichromate, phosphoric acid or phosphate. The coated sheets
are then dried.
It is an object of the present invention to produce
steel sheets for forming which have a good corrosion resistance
after forming by uniformly coating with the above solution.
Generally, when steel sheets are formed, liquid wax, `
lubricating oils, organic high polymers, etc., are coated on the
steel before forming in order to prevent rupturing and scuffing
during the forming. In the above-mentioned methods, compllcated ;
processes such as a cleaning and drying are required after form- ~; ;
ing in order to remove lubricants and to make matters worse, the
corrosion resistance of the part which is sub~ected to forming
decreases considerably, however, no better method is presently
known.
On the~other hand, plating of steel sheets is sometimes
i used to prevent the decrease of corrosion resistance after form-
`! ing. For instance, galvanized steel sheet and electrogalvanized
sheet are widely used because the zinc plating on sheets gives a
remarkable corrosion resistance to the base steel, however, zinc-
plated steel sheets are not satisfactory in formability, for
some cracks occur in drawing ratio 2 without coating of lubricat-
ing oil. Also in a lower drawing ratio than the 2.0, the plated
layer in the part to be formed is destroyed to a great extent and
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consequently corrosion resistance deteriorates considerably to
almost the same level of the base steel sheets without the
plated layer. However, the occurrence of cracks during drawing
can be somewhat reduced by coating the electrogalvanized sheets
with machine oil or press oil during drawing. In this case, an
oil coating process and a cleaning process are required and
these processes contribute to low productivity. Moreover, the
corrosion resistance at the drawn part deteriorates noticeably.
These methods are referred in published Japanese patent
applications ~os. Sho 45-5130 and 49-24789, which applications
are the starting point of the present invention. '
Published Japanese patent application No. Sho 45-5130
disclo~es a method of coating steel sheets with solution which
mainly consists of lithium silicate in order to increase corro-
sion re~istance, however, this method provides no irnproved
,effects on formability of the sheet, and in fact, the sheet by
this method requires lubricating oil during deep drawing because
of i.ts poor formability.
Published Japanese patent application No. Sho 49-24789
discloses a method to improve formability of metal plates and to
prevent occurrence of defects during forming, by first coating a
watex glass film on a steel sheet and then coating with a solu-
tion of solid wax dissolved in an organic solventl then followed
by drying. '~'
This method of making a dual layer by two coatings is
very complicated and the corrosion resistance after forming is
merely temporary, i.e. it only remains until the next surface
treating process, because it is designed so that the coated films
can be easily removed by hot water and not be permanent.
On the contrary, the present invention avoids these
defects arising from forming of steel sheets.
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In accordance with the present invention, there is
~provided a method of treating steel sheets which have good
corrosion resistance after forming, which comprises coating a :
steel sheet with a solution which contains
a) water-soluble or water-dispersible lithium silicate at
a concentration of 2 to 250 g/l, which lithium silicate is a
mixture of silicic acid or silicate and lithium salt in a molar
ratio of 20 : 1 to 1
b) at least one water-soluble or water-dispersible ~
10 saturated or unsaturated fatty acid compound, higher alcohol : :
wax, polyethylene type resin, fluorine type resin or silicone ~ ;
type resin at a concentration of 1 to 250 g/1.
The application o~ the present invention omits the
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processes of oil coating and cleaning, and forms a strong coat-
ing film which contains lithium compound, so that a steel sheet
with the film of the present invention can be formed without
reducing the corrosion resistance after forming. Moreover, a
point of advantage of the present invention is -the possibility
of handling the steel sheet without contaminating the surface
with the dirt, i.e. fingerprints, because the film formed by the
method of the present invention is solid and difficult to dissolve. -
Further, the solution used in the present invention is water-
based, and has an advantage in safety and sanitation.
Thè present method involves coating a steel sheet with
a solution which contains at least one or more water-soluble or
water-dispersible lithium silicates prepared from silicic acid
or a silicate and a lithium salt, e.g. the hydroxide and at
least one or more water-soluble or water-dispersible saturated
or unsaturated ~atty acid compounds, higher alcohol waxes, poly-
ethylene type resins, fluorine type resins, silicone type resins,
or and if desired, one or more of water-soluble chromic acid,
chromate, dichromate, phosphoric acid and phosphate, onto the
steel sheets. Then the coated sheet is dried immediately.
It is preferred that lithium silicate used in the present
invention is water-soluble or dispersible and is prepared from
a mixture of silicic acid or silicate and lithium salt in a
molar ratio of 20:1 to 1:1. Lithium ion itself has the character-
istic role of promoting the solidification and insolubility of
treated film, and contributes to the formation of film with
superior corrosion resistance. Therefore, lithium silicate
which is prepared using lithium hydroxide at a lower ratio than
the above-mentioned, exhibits a tendency to decrease corrosion
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resistance and retard hardening of the film with solidification. ~-
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Conversely, the treating solution has a tendency to be gelled at
a higher ratio than the above-mentioned. ~-
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Lithium silicate may be prepared according to the
following, sodium or potassium silicate, or silicate sol which
is commercially available as silicic acid or silicate, and
lithium hydroxide are respectively weighed and mixed together
in the above-mentioned ratio. Further, commercially available
water-soluble or water-dispersible lithium silicate, i.e. which
is already mixed together may be employed, e.g. Snowtex*of Nissan
Chemical Industries, Ltd. A concentration of lithium silicate
in the range of from 2 to 250 g/l is suitable for the treatment
solution of the present invention, A film formed by the solution
with the above-mentioned concentration gives superior corrosion
resistance and prevents adherence of dirt, e.g. fingerprints, on
the surface in handling, press-for~ing, etc.
At a concentration o~ less than 2 g/l, the effects
mentioned above cannot be expected. At a concentration of more
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than 250 g/l, the improvement in corrosion resistance is not in
proportion to the increasing concentration, and on the contrary,
the treated film exhiblts a remarkably poor effect on the form-
ability of a steel sheet.
Next, the water-soluble or water-dispersible lubricant
i~ added to the solution o~ lithium silicate in order to improve~
the formability o~ the steel sheet.
These lubricants may include the following agents,
saturated fatty acid compounds, e.g. esters or salts such as
stearates, palmitates and myristates, unsaturated fatty acid
compounds, e.g. esters or salts such as oleates and linolates,
higher alcohol type waxes such as melissyl alcohol, tetracosanol
and stearyl alcohol; polyethylene type resins such as various
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kinds of polyethylene resin with 5,000 - 40,000 molecular wei~ht;
fluorine type resins such as tetrafluoroethylene, chlorotrifluoro-
ethylene and fluorovinylidene resins, silicone type resins such as
dimethylpolysiloxane, methylhydrodien polysiloxane and silicone
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alkyd varnish. The kreatment solution comprises one or more of
these agents.
The concentration in the range of 1 to 250 g/l is suit-
able for improving the formability. The concentration of less~
than 1 g/l gives little effect on improvement of the~formability,
conversely the concentration of more than 250 g!l imparts a
remarkably bad influence on the corrosion resistance, makes it
easy to contaminate the surface with the dirt, i.e. fingerprints
in handllng, press-forming, and glves the finished surface sheet
; 10 a poor appearance.
For the purpose of further improving corrosion resist-
ance, at least one agent selected from soluble chromic acid,
chromate, dichromate, phosphoric acid and phosphate are added
to the above-mentioned solution. Suitable compounds include
chromates and dichromates containing hexavalent chromium such
as chromic acid, sodium chromate, ammonium chromate, sodium
bichromate and ammonium bichromate. The phosphates include
monosodium (hydrogen) phosphate, disodium (hydrogen) phosphate,
ammonium phosphate, potassium phosphate, etc.
A concentration in the range of 1 to 100 g/l is suit-
able for achieving the increase of the corrosion resistance. A
concentration of less than 1 g/l imparts no improvement in the
corrosion resistance, and a concentration of more than 100 g/l
is unfavorable because further improvement is not realized, the
cost is high and the treatment solution has a tendency to be
...
unstable and susceptible to gellation. ~
Water-soluble organic high polymers, or surface active ~ -
agents including non-ionlc, anionic and cationic types, may be
also added to the treatment solution in order to disperse the
lubricant uniformly in the treatment solution, or to improve
wetting of the steel sheet with the treatment solution.
A temperature of 25C to 70C is suitable for treating
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with the solution. A temperature of less than 20C-may be not
necessarily unsuitable, but it has a disadvantage in requiring
a longer time to dry. On the other hand, at a temperature of
more than 70C, it is difficult to keep the concentration of -
bath constant by reason of a higher vaporation, which makes the
bath unstable and susceptible to gellation.
A steel sheet may be coated with the solution by dipping,
spraying as well as roller-coating, and it is dried after coat-
ing. Although drying at room temperature is suitable for appli-
cation of the present invention, it is desirable to dry by forcerather than naturally at room temperature, thereby avoiding long
drying times. Especially when polyethylene, fluorine or silicone
type resins are used as lubricants, it is desirable to dry by
force at a kemperature of 80C to 200C. The thic]cness of a
treated film, which is mainly controlled by the concentration
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of lithium silicate and addition agent, becomes thicker in
proportion to the increasing concentration.
The present invention is applicable to an electrolytic
zinc, chromium, tin, copper, nickel, aluminum and other metal
, 20 plated steel sheets as well as to cold rolled steel sheet. Also
; the present invention is applicable to those steel sheets with a
post-treatment such as with chromate, phosphate and so Eorth.
The detailed effects of the present invention will now
be explained taking into account the following practical, non-
limitative examples.
EXAMPLE 1
A low carbon steel sheet of 0.5 mm thickness, after
annealing and temper rolling, was dipped into the following
solution, and was dried with a hair dryer at about 70C to form
a film.
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Treatment Solution
Lithium silicate which consists of a
mixture;of silicic acid and
lithium hydroxide in a molar ratio
of 8 : 1 150 g/l
Sodium stearate 7 g/l
Sodium chromate 50 g/l
Epan-785*(non-ionic surface active
agent produced by Dai-Ichi Kogyo
Seiyaku Co., Ltd.) 3 g/l
Temperature of the solution 40C
The sheet, after treatment in the above solution, was
blanked to form a disk specimen 80 mm in diameter, was drawn
deeply in a drawing ratio of 2 by means of a punch and die, and
was evaluated ~or corrosion resistance of the deEormed part.
In ca~e of the deep drawing, a steel sheet which was not treated
with the above solution cannot be drawn free from rupture without
No. 620 machine oil as lubricant, while the sheet treated in the
solution of the present invention can be drawn successfully with-
out any lubricants. Subsequently the salt spray test providedby JIS Z 2371 was applied to these two drawn parts. The drawn
part without the treating in this solution was covered with red
rust a~ter 10 minutes, while the drawn part treated in the solu-
tion of the present invention did not show any red rust even after
2 hours.
- It was also found from the humidity exposure test at a
; temperature of 50C, and relative humidity of 95%, that the
drawn part without treating in this solution showed rust after
an hour: on the contrary, the drawn part with treat1ng in this
solution did not show any rust after 24 hours~
EXAMPLE 2
A low carbon steel sheet of 0.5 mm thickness was cleaned
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and pickled for pre-treatment by a conventional method. The -
sheet was then electrogalvanized as described below and was
then treated as follows:
~1) dipping in the solution described below,
(2) squeezing by a wringer roll, immediately followed
by force drying at 150C for 5 seconds.
On the other hand, an electrogalvanized sheet, which
was not processed according to the present invention, was treated
with a conventional chromate solution so as to be coated with an
0.5 mgjdm2 chromium film on the surface.
(1) The conditions for electrogalvanizing:
Zinc sulfate 2S0 g/l
Sodium sulfate 30 ~/1
Aluminum sul~ate 20 g/l
~, Temperature of the electrolyte ~0C
Current Density 20 A/dm
Plating time 20 seconds
,~ (2) Composition of the treatment solution:
Lithium silicate which consists of a
mixture of silicic acid and lithium
hydroxide in a molar ratio of 8 : 1 230 g~
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Tetracosanol ( Trade mark: SAIVINOR
DP - 12B, produced by Saiden Chemical
Ind. Co., Ltd.) 150 g/l
Sodium dichromate 10 g/l
Temperature of the solution 45C
Both the electrogalvanized sheet subjected to the -
present invention and the electrogalvanized sheet with the
conventional chromate treatment were blanked to form a disk
specimen 120 mm in diameter, and were pressed to a cylindrical
shell by means of a punch 69 mm in diameter and die. The sheet
with only conventional chromate treatment was ruptured during
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pressing without the use of lubricating oil. Conversely the
sheet which was treated in the solution was not ruptured, and
showed little scuffing on the sur~ace even without lubricating .
oil.
The salt spray test as described in Example 1 was
applied to the cylindrical shell wall in order to evaluate its
corrosion resistance. Before the tes-t, the test piece from the
cylindrical shell with the chromate treatment was cleaned with
trichloroethylene vapor. The rust on the test piece was observed
10 after 24 hours, while rust on test piece from the cylindrical
shell wall which had been treated in this solution was observed
only after 70 hours.
In the humidity exposure test as described in Example 1,
rust was observed on the side wall of the former after ~0 hours,
while no rust was found in the latter after 300 hours.
EXAMPLE 3 '
; A low.carbon steel sheetl 0.5 mm in thickness, was .
. electrogalvanized by the electrogalvanizing treatment described :~
in Example 2, to give a coating of 12 g/m . Subsequently it was
dipped in the following solution, and was dried by force at 120C. :
Treatment Solution
Lithium silicate which consists of a
mixture of sodium silicate cmd lithium
. hydroxide in a molar ratio of 20 : 1 50 g/l
-~ Polyethylene (molecular weight: about :-
12,000) . 200 g/l
~ Sodium phosphate 5 g/l :. :
`~ Temperature of the solution ~0C
The electrogalvanized sheets which were treated in the --
above solution were blanked to form a disk specimen 120 mm in ; :
~, diameter and were pressed to a cylindrical shell by means of a
punch, 69 mm in diameter and die in the same way as described
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in Example 2. As a result of the pressing, it was proved that
the sheet wi-th the film of the present invention showed no
rupture and little scuffing on the side wall of cylindrical
shell, even without lubricating oil.
The sheet cut from the side wall of the cylindrical
shell was evaluated by the salt spray test and the humidity
exposure test as described in Example 1. The results showed
that no rust was observed after 50 hours in the salt spray test
and no rust after 200 hours in the humldity exposure test.
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