U.S. patent number 3,663,383 [Application Number 04/734,801] was granted by the patent office on 1972-05-16 for method for manufacturing painted metal sheet.
This patent grant is currently assigned to Yawata Econ Steel Co., Yawata Iron & Steel Co., Ltd.. Invention is credited to Megumi Koyama, Shozo Matsuda, Kouzou Murayama, Joji Oka, Royji Takahashi, Tadashi Tanaka, Kunimitsu Yamamoto.
United States Patent |
3,663,383 |
Matsuda , et al. |
May 16, 1972 |
METHOD FOR MANUFACTURING PAINTED METAL SHEET
Abstract
A method for manufacturing a painted metal sheet by successive
paintings comprises the steps of (a) subjecting a metal sheet
plated with zinc or zinc alloy to an electrophoretic treatment with
a water-soluble resin series paint to provide an undercoating, then
(b) painting the steel sheet having the electro-deposited paint
coating with a water-soluble or solvent-soluble paint to provide a
final coat, and then (c) baking and drying the undercoat and the
final coat at the same time. Step (a) may optionally be preceded by
a step of subjecting the initial metal sheet, plated with zinc or
zinc alloy, to a chemical-synthetic treatment to form a foundation
for subsequent painting.
Inventors: |
Matsuda; Shozo (Kawasaki City,
JA), Tanaka; Tadashi (Kawasaki City, JA),
Murayama; Kouzou (Matsudo City, JA), Yamamoto;
Kunimitsu (Matsudo City, JA), Oka; Joji (Kawasaki
City, JA), Takahashi; Royji (Katsushika-gun,
JA), Koyama; Megumi (Matsudo City, JA) |
Assignee: |
Yawata Iron & Steel Co.,
Ltd. (Tokyo, JA)
Yawata Econ Steel Co. (Tokyo, JA)
|
Family
ID: |
27288919 |
Appl.
No.: |
04/734,801 |
Filed: |
June 5, 1968 |
Foreign Application Priority Data
|
|
|
|
|
Jun 5, 1967 [JA] |
|
|
42/35900 |
Jun 12, 1967 [JA] |
|
|
42/50450 |
Jun 19, 1967 [JA] |
|
|
42/39147 |
|
Current U.S.
Class: |
204/488 |
Current CPC
Class: |
C25D
13/20 (20130101); B05D 7/542 (20130101); C25D
13/22 (20130101); B05D 2252/02 (20130101); B05D
1/28 (20130101); B05D 2202/00 (20130101); B05D
1/007 (20130101); B05D 2252/10 (20130101) |
Current International
Class: |
C25D
13/22 (20060101); C25D 13/20 (20060101); B05D
7/16 (20060101); B01k 005/02 (); C23b 013/00 () |
Field of
Search: |
;204/181 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
|
|
|
|
|
|
|
1,405,550 |
|
May 1965 |
|
FR |
|
1,073,965 |
|
Jun 1967 |
|
GB |
|
Primary Examiner: Williams; Howard S.
Claims
What is claimed is:
1. A method for manufacturing a painted metal sheet by successive
paintings which comprises the steps of subjecting the metal sheet
to an electrophoretic painting with an aqueous paint as an
undercoating painting, rinsing and wind-drying the undercoat formed
by the electrophoretic painting and then subjecting the resultant
undercoated metal sheet to a non-electrophoretic final painting
with an organic solvent-soluble thermosetting paint and thereafter
baking the resultant electrodeposited undercoat and final coat
together in a single baking step.
2. A method for manufacturing a painted metal sheet by successively
painting flat metal sheet or strip coil which is plated with zinc
or zinc alloy, which comprises the steps of subjecting the said
metal sheet or strip coil to an electrophoretic painting with a
water-soluble acrylic resin series paint as a underpainting,
rinsing and wind-drying the undercoat formed by the electrophoretic
painting, and immediately thereupon non-electrophoretically
painting the undercoated metal sheet or strip coil with at least
one kind of thermosetting paint selected from the group consisting
of the organic solvent-soluble phenol resin series, the melamine
resin series, the alkyd resin series, the acrylic resin series and
the vinyl resin series or their copolymers as the final painting
and then baking the resultant electrodeposited undercoat and final
coat together in a single baking step.
3. A method for manufacturing a painted steel sheet or strip coil
by successively painting steel sheet or strip coil which is plated
with zinc or zinc alloy, which comprises the steps of subjecting
the steel sheet or strip coil to an electrophoretic painting by
dipping the same into a water-soluble electrodepositing treating
bath, said bath consisting of a water-soluble resin, which is
composed of acrylic ester and/or methacrylic ester and its ammonium
salt or amine salt, and a water-soluble chromium compound added in
an amount of about 0.01 to 5.0 weight percent to the said resin,
rinsing and drying the undercoat formed by the electrophoretic
painting, when the coat is deposited in an amount of 150
mg/dm.sup.2, and immediately thereupon non-electrophoretically
painting the undercoated steel sheet or strip coil with at least
one kind of thermosetting paint selected from the group consisting
of phenol resin series, melamine resin series, alkyd resin series,
acrylic resin series and vinyl resin series or their copolymers as
the final painting and baking the resultant electrodeposited
undercoat and thermosetting final coat at the same time in a single
baking step and cooling the resultant product.
4. A method as claimed in claim 3, wherein a water-soluble
phosphoric acid series additive or boric acid series additive or
pigment is added to the electrodepositing treating bath.
5. A method as claimed in claim 4, wherein the steel sheet or strip
coil which is plated with zinc or zinc alloy, is further subjected
to a phosphate treatment or chromate treatment or other coat
treatment to obtain a phosphate coat or chromate coat or a coat
having high electric resistance at the outermost layer.
6. A method for manufacturing a painted steel sheet or strip coil
by successively painting steel sheet or strip coil, which is plated
with zinc or zinc alloy, which comprises the steps of subjecting
the steel sheet or strip coil to a chemical-synthetic treatment to
obtain a coat having a high electric resistance, then subjecting
the chemical-synthetically treated steel sheet or strip coil to an
electrophoretic painting with a water-soluble paint or a
water-dispersed paint, while keeping the electric resistance of the
chemical-synthetically formed coat to below 10.OMEGA. cm.sup.2,
rinsing and wind-drying the undercoat formed by the electrophoretic
painting and then subjecting the resultant undercoated steel sheet
or strip coil to a non-electrophoretic final painting with an
organic solvent-soluble thermosetting paint as the final painting
and thereafter baking the resultant undercoat electrodeposited and
the thermosetting final coat together in a single baking step.
7. A method as claimed in claim 6, wherein the electric resistance
of the chemical-synthetically formed coat is kept to below 5.OMEGA.
cm.sup.2.
8. A method for manufacturing a painted steel sheet or strip coil
by successively painting steel sheet or strip coil which is plated
with zinc or zinc alloy, which comprises the steps of subjecting
steel sheet or strip coil to an electrophoretic painting after
optional chemical-synthetical treatment, in advance, while
regulating the contact rolling pressure between the steel sheet or
strip to be treated and a conductor roll so that it is above about
100 kg per one meter width of the steel sheet or strip coil,
rinsing and wind-drying the undercoat formed by the electrophoretic
painting and then subjecting the resultant undercoated steel sheet
or strip coil to a non-electrophoretic final painting with an
organic solvent-soluble thermosetting paint and thereafter baking
the resultant undercoat electrodeposited and the thermosetting
final coat together in a single baking step.
9. A method as claimed in claim 8, wherein the contact rolling
pressure between the steel sheet or strip coil to be treated and
the conductor roll is regulated to be more than about 300 kg per
one meter width of the steel sheet or strip coil.
10. A method for manufacturing a painted steel sheet or strip coil
by successively painting steel sheet or strip coil, which is plated
with zinc or zinc alloy, which comprises the steps of subjecting
the steel sheet or strip coil to a chemical-synthetical treatment
to obtain an undercoat as a foundation for painting which has high
electric resistance, and then subjecting the chemical-synthetically
treated steel sheet or strip coil to an electrophoretic painting
with a water-soluble paint or a water-dispersed paint, while
removing solidified melt stuck to the surface of a conductor roll,
to which electricity is supplied, such as zinc or zinc oxide, by
means of a doctor blade, immediately after it has stuck to the
surface of the conductor roll and arranging the surface of the
conductor roll, which is brought into contact with the said steel
sheet or strip coil, rinsing and wind-drying the resultant
undercoat formed by the electrophoretic painting and then
subjecting the resultant undercoated steel sheet or strip coil to a
non-electrophoretic final painting with an organic solvent-soluble
thermosetting paint as the final painting and thereupon baking the
resultant undercoat electrodeposited and the thermosetting final
coat together in a single baking step.
Description
The present invention relates to a method for manufacturing a
painted metal sheet by a method involving baking the steel metal
sheet after the application of successive coatings of paint
thereon.
Heretofore, in manufacturing a painted metal sheet there has
usually been adopted a so-called "one coating -- one baking"
method, using a sprayer or a roll coater. In this case, however, as
the painting is carried out only one time, the product of this
method was defective in corrosion resistance due to an unavoidable
formation of pin holes. Consequently, when anticorrosiveness and
workability are particularly required, a so-called "two coating --
two baking" method had to be adopted.
Besides, there has been applied another method, for instance, a
"two coating -- one baking" method, in which a final painting and a
subsequent baking are carried out immediately after an undercoating
has been completed, while the resultant undercoat is still in the
wet state. By applying this method, it is made possible to reduce
pin holes but, on the other hand, it is not possible to manufacture
a thick coat because of the necessity of painting the metal sheet
while rotating a painting roll in the same direction as the moving
direction of the metal sheet, and further it is also not possible
to obtain the improvement in coat properties to be expected from
duplicated paintings, because heterogeneous paints can not be
used.
On the other hand, when applying the "two coating -- two baking"
method to the painting of a metal sheet or coil, there can be
obtained following advantages that pin holes can be reduced, any
suitable paints can be selected for the undercoating and final
coating respectively according to the use, and a thick coat can be
formed; hence a painted metal sheet having excellent
anticorrosiveness as well as adhesiveness can be obtained. However,
this method also has disadvantages in that it requires two roll
coating machines and two baking furnaces with the result of a sharp
increase in equipment costs, the control of the painting becomes
difficult on account of the increased length of the painting lines,
the frequency of producing inferior products becomes high, and
metal sheets to be scrapped because of inferior products
increase.
The aim of the present invention is to eliminate the various
drawbacks of conventional methods as the above-mentioned ones; and
the basic idea underlying the present invention resides in that at
first an undercoating is provided with a water-soluble paint by an
electrophoretic painting step, and immediately after rinsing and
wind-drying the resultant undercoat a water-soluble or
solvent-soluble paint is applied to the undercoat in a proper
manner and thereupon the thus-painted steel sheet or coil is baked
once to produce a final product.
That is, one of the main objects of the present invention is to
provide a painting method, in which successive formations of two or
more paint coats on the surface of a metal sheet can be carried out
without interposing a baking between the undercoating and the final
coating by subjecting the metal sheet to an electrophoretic
painting with a water-soluble or water-dispersed paint to form an
undercoat, because the water content of the paint for the
undercoating can be made so small by the electrophoresis that the
whole surface of the undercoat can be wind-dried in a very short
period of time, which makes it possible immediately to apply the
final coat to the undercoat in succession without baking the
undercoat. This method of the present invention is attended with
the advantages that, as a paint of another kind can be used for the
final coating, excellent anticorrosiveness and adhesiveness of the
painted metal sheet can be obtained, the baking can be carried out
with one baking furnace and the painting line can be made short,
which bring favorable effects on the control of equipment and of
the painting operation.
The second main object of the present invention is to provide a
painting method, in which flat metal sheet or strip coil is
subjected to an electrophoretic painting with a water-soluble
acrylic resin series paint to form an undercoat and immediately
thereupon the final painting is carried out by applying a
solvent-soluble thermosetting paint to the undercoat without baking
the electrodeposited undercoat.
The third main object of the present invention is to provide a
painting method, which is the most practical method for
successively painting a metal sheet and in which a steel sheet or
strip coil plated with zinc or zinc alloy (hereinafter referred to
as "galvanized steel sheet") is optionally subjected to a
chemical-synthetic foundation treatment such as a phosphate
treatment or chromate treatment before it is subjected to the
electrophoretic painting. Then, the chemical-synthetically treated
galvanized steel sheet or the galvanized steel sheet is dipped in
an electrodepositing bath to obtain an electrodeposited undercoat.
Immediately after the electrodeposition treatment, the steel sheet
is dried by simply blowing air on it (without baking) and then a
solvent-soluble thermosetting paint, e.g. one of the phenol series,
melamine series, alkyd series, acrylic series and vinyl series is
applied on the electrodeposited undercoat. Finally, both coats,
that is, the electrodeposited undercoat and the finish
solvent-soluble paint coat, are baked at a single stroke, thereby
to obtain colored galvanized steel sheet.
As to the electrodepositing bath to be used in the above-mentioned
third process step of the present invention, that of the following
composition is to be recommended as the most effective one, that
is, a bath which is mainly composed of a water-soluble resin,
containing as main ingredients lower alkyl ester of acrylic acid
and/or lower alkyl ester of methacrylic acid and their ammonium
salt or amine salt, and a water-soluble chromium compound added in
an amount of 0.01 to 5.0 weight percent to the said water-soluble
resin.
The role of this water-soluble electrodepositing bath to be played
in the method of the present invention is overwhelmingly important
and is inseparably connected with the method of the present
invention.
In the following, therefore, the electrodepositing bath
(hereinafter referred to also as "electrodepositing paint" or
"electrophoretic paint") will be explained in detail.
In conventional methods of coating metal articles with organic
compounds by electrophoresis, there have been mainly used
water-dispersion series paints and water-soluble water-solution
series paints. As for the water-dispersion series paint a
dispersion or emulsion of high organic high molecular compound is
employed, and as for the water-solution series paint alkali metal
salts of the acrylic series, melamine series, alkyd series or
maleic oil series compounds are employed, and many of them are
already known through various patents relating thereto and
others.
However, recently various investigations have been made to improve
the painting method by treating a steel sheet in a treating bath,
in which a water-soluble chromium compound is added to a
water-soluble high molecular compound to obtain a painted steel
sheet having excellent anticorrosiveness and durability after
baking the painted steel sheet.
The present invention is a development of these investigations and
is distinguished by the following features:
The first feature of the present invention resides in the novelty
of the electrodepositing bath employed in the process of the
present invention, in which the compounding ratio of water-soluble
acrylic copolymer or methacrylic copolymer containing water-soluble
chromium compound added thereto is specified, whereby it is made
possible to attain an increased insolubilization reaction, the
formation of a particularly excellent anticorrosive coat, an
increase in electrodepositing efficiency and an excellent throwing
power and the like, when carrying out the electric-deposition in
the said bath. The second feature of the present invention is that
the undercoat obtained by the electrodepositing paint itself not
only has an excellent atmospheric corrosion resistance but also
imparts an excellent working adhesiveness and anticorrosiveness to
an ordinary paint coat formed on the undercoat. The third feature
of the present invention, which is the most important feature of
the present invention, is that the most serious problem any
conventional anodic chemical-synthetic treatment by means of
electrophoresis must confront, that is, the difficulty in treatment
control caused by strong alkaline ingredients concentrated on the
cathode in the conventional treatment, does not occur in
practically operating the method of the present invention. This
seems to be attributable to the excellent stability of the treating
bath of the present invention at a high temperature.
The paint used in the electrodepositing operation of the present
invention is a water-soluble organic high molecular compound such
as copolymer of alkali metal salt of acrylic acid or amine or
ammonium salt of methacrylic acid usually copolymerized with lower
acrylic ester, preferably lower alkyl ester of about four carbon
atoms or lower methacrylic ester, preferably lower alkyl ester of
about four carbon atoms, and in some case further a third compound,
if necessary. In this case, the ester radical is not subjected to
any particular restriction.
The viscosity of this copolymer resin is preferably less than
10,000 CPS in 30 percent aqueous solution. The higher the degree of
polymerization, the better the working adhesiveness,
anticorrosiveness and durability of the coat obtained thereby.
However, if the viscosity is more than 10,000 CPS, there occurs a
remarkably difficulty in the treatment and further the
electrodeposition of the paint becomes excessive, resulting in a
deterioration in the rinsing effect. The range of the viscosity is
advantageously in the range of from 2,000 to 6,000 CPS. This range
is the most suitable from the points of working adhesiveness and
other properties of the deposited coat, and an amount of
electrodeposition and a rinsing effect. The alkali salt in the
copolymer is necessary to be less than 50 percent from the stand
point of properties of the coat obtained, but is usually used in an
amount of about 3 to 5 percent from the necessity of
water-solubilization.
Metals to be treated in the bath used in the process of the present
invention cover iron and steel products, that is, iron and steel
themselves, melting zinced steel sheet, electro-galvanized steel
sheet, tin-plate sheet, aluminum-plated steel sheet, turnplate
sheet. More precisely, the electrophoretic treatment of the present
invention is applied not only to the surface of iron and steel
sheet, but also of aluminum-, zinc- or tin-plated steel sheet and,
more advantageously to zinc- or zinc alloy-plated steel sheet which
is further coated with a chemical-synthetic film by a foundation
treatment for painting such as phosphate treatment or chromate
treatment. In these cases, metal ions flow out in the solution and
react immediately with copolymer of acrylic aid or methacrylic acid
and with water-soluble chromic acid ions or bichromic acid ions,
and the resultant salt is uniformly dispersed in the coat, which
accelerates the gelation of the coat and later acts as an oxidizing
agent for effecting and accelerating the bridging reaction by the
subsequent treatment of drying the steel sheet by heating.
Therefore, the mixing ratio of chromium compound to be added to a
water-soluble organic high molecular compound such as acrylic acid
copolymer or methacrylic acid copolymer is sufficient with only
about one-fifth to one-tenth of that in the case of a simple
chromate treatment. More concretely, a proper mixing ratio of
chromium compound to be applied in the anodic treating bath
(electrodepositing paint) is 0.01 to max. 5 weight percent of the
above-mentioned water-soluble organic high molecular compound, as
calculated in terms of chromium (if below 0.05 weight percent, the
deposited coat will be sporadic). An excellent anticorrosiveness
can be obtained specially in the range of 0.01 to 1 weight
percent.
If the chromium ion concentration is increased to some degree, a
passivating tendency appears at the time of electrodeposition,
whereby it becomes difficult to obtain a sufficient thickness (for
instance, 10 to 100 mg/dm.sup.2), causing a deterioration of the
anticorrosiveness, and if the chromium ion concentration is lowered
too much, the chromic acid concentration in the paint coat is
reduced, whereby the bridging of the paint coat will be
insufficient, which causes the deterioration of working
adhesiveness and anticorrosiveness.
As for chromium compounds to be added there may be enumerated
water-soluble chromate or bichromate of ammonium, alkali metal,
alkaline earth metal, or the third group metal. Practically
chromates or bichromates of ammonium, magnesium, strontium,
gallium, aluminum or the like are used.
The treating bath containing 1 to 30 percent of organic high
molecular compound (in terms of the non-volatile part) is
practically used, but is not subjected to a particular limitation
from the point of the formation of the coat. The pH value of the
treating bath is used mainly in the alkaline state. The pH value
which is most suitable for practical use is about 8.0.
If the content of the organic high molecular compound (in terms of
the non-volatile part) is about 30 weight percent, the viscosity of
the surface coat of the article taken out from the treating bath
will become too high, while if the content is below 1 weight
percent, the efficiency of electrodeposition will be
deteriorated.
The concentration of water-soluble resin of the electrodepositing
paint suitable for practical use is in the range of 5 to 30 weight
percent, preferably 10 to 15 weight percent. If the concentration
of the vehicle exceeds 30 weight percent, the viscosity of the
paint will increase rapidly and the painting loss will increase and
also the minuteness of the coat will be lost. On the other hand, if
the concentration of the vehicle is below 5 weight percent, the
Coulomb's efficiency will be remarkably reduced, the thickness of
the paint coat obtained at a normal electrodeposition voltage will
become thin, resulting in the reduction of the
anticorrosiveness.
The electrodeposited coat is required to be of such a thickness
that it can be dried in a short period of time by drying (hot
wind-drying or compulsive wind-drying) which is to be carried out
after rinsing subsequent to the electrodeposition. That is, the
electrodeposition should be carried out to such a degree that the
resultant coat may reach the thickness of max. 150 mg/dm.sup.2,
desirably 20 to 90 mg/dm.sup.2. The electrodeposition is followed
by rinsing and drying, and thereupon the final painting by a
solvent-soluble or water-soluble paint is carried out. As for the
paint for the final painting there may be enumerated those of the
thermosetting acrylic resin series, vinyl-denatured acrylic resin
series, alkyd-denatured resin series, vinyl chloride resin series,
and denatured alkyd resin series. Among these, vinyl-denatured
acrylic resin series paints show the best results in adhesiveness
and anticorrosiveness.
In the following we shall explain the basic process of the present
invention with reference to the attached drawing showing the
process steps. As is shown in the accompanying FIGURE of drawing
illustrating the steps of the process of the present invention in
series, a steel sheet 1 loosened by an uncoiler 2, said steel sheet
being subjected to or not yet subjected to a surface treatment, is
transferred through a guide roll 3 and a pinch roll 4 to a vessel 5
for degreasing and hot-water rinsing, wherein physical and chemical
surface regulations are carried out, and then transferred through a
roll 6 made of nylon series resin to a bonderising vessel 7. After
the bonderising, the steel sheet 1 is then passed through a machine
8 for electrophoretic painting, wherein the water-soluble paint is
regulated to be of a concentration suitable for the electrophoretic
painting (for instance, to the concentration of about 15 weight
percent), and there is applied an electric current of a determined
voltage turned to a coil speed of the line so that an amount of the
paint deposited on the steel sheet is 10 to 100mg/dm.sup.2.
As for water-soluble paint, any paint of the acrylic ester series,
phenol alkyd series and the like may be used. After the steel sheet
is coated with a determined water-soluble paint in the machine 8
for electrophoretic painting, it is then rinsed in a vessel 9 for
rinsing and then lightly dried in a drying machine 10, which is
provided with a wind box to dry the steel sheet by wind at room
temperature. In this case, the drying is carried out by properly
regulating the amount and temperature of the wind in accordance
with the speed of the line.
The steel sheet, the undercoating of which has thus been completed,
is then subjected to a finish painting according to per se
conventional methods, for instance, it is led by guide rolls 11 and
12 to a roll coating machine 13, wherein a finishing is
performed.
As for the paint for the finishing there may be mentioned paints of
the thermosetting synthetic resins such as phenol, melamine, alkyd,
acryl, vinyl chloride and the like, said paints being so diluted by
solvents to such a viscosity as suitable for the finishing (for
instance, 30 to 150 sec./20.degree. C. according to Fordcup No. 4).
The paint as above-mentioned is applied on the steel sheet by
regulating distances of the roll coater so that the dried coat has
the thickness of 1 to 30 microns. 14 is a roll coating machine for
painting the reverse (however, by carrying out the electrophoretic
painting double painting of the reverse may be omitted). The
finish-painted steel sheet is passed through a drying oven 15
having a hot wind heated up to a temperature of 150.degree. to
250.degree. C., wherein both the undercoat and the final coat are
simultaneously baked.
The baked steel sheet is water-cooled in a water-cooling vessel 16
and transferred to a recoiler 18 through a pinch roll 17 to coil
the steel sheet.
The bonderising step included in the above-mentioned process is a
particularly advantageous foundation treatment, but is not a
requisite condition. Therefore, it can be replaced by a chromate
treatment or any other chemical-synthetic treatment, or it may be
even omitted as the case may be. Further, it is, of course, evident
that as for the paint for the finishing a water-soluble paint of a
kind different from that for the undercoating may be applied.
However, in the practical operation of the process of the present
invention, besides the basic steps as above-mentioned, the
following three additional steps facilitate and secure the
operation.
The first additional process is as follows:
In the successive painting of a strip steel sheet plated with zinc
or zinc alloy (including galvanized steel sheet, melting
zinc-plated steel sheet and the like) according to the method of
the present invention, the steel sheet coated with a zinc layer or
zinc alloy layer is subjected to a phosphate treatment or other
chemical-synthetic treatment or other coat treatment which has a
high electric resistance prior to the electrophoretic painting with
a water-soluble paint or water-dispersed paint, the method of the
present invention is characterized by maintaining the electric
insulation resistance at the coat formed on the surface of the
galvanized steel sheet by the chemical-synthetic treatment or the
coat treatment of a high electric resistance to below 10.OMEGA.
cm.sup.2, when effecting the electrodeposition, and then carrying
out the final painting on the electrodeposited coat and baking the
electrodeposited undercoat and the final coat at the same time.
In the case of the successive painting of a metal sheet, contrary
to a general electrodeposition painting, a conductor roll is
required as a device for supplying electricity to the metal sheet.
In this case, if an electric current and a voltage to be supplied
reach great values, due to the rise in the speed of the successive
painting, there occur various troubles between the conductor roll
and the material to be electrodeposited such as, for instance,
occurrence of arc spots and melting out of the conductor roll.
This first additional step is to eliminate these troubles which may
be caused at the conductor roll. In the following this additional
step will be explained in detail by referring to concrete
examples.
The application of the electrodeposition painting to an iron and
steel product, particularly to a galvanized steel sheet, which is
further chemical-synthetically treated, has proved to show much
better results in achieving the uniformity of the paint coat and
high speed painting as compared with the case of a conventional
painting by using usual paint.
At present, the painting speed, which is in general use, is about
30 to 60 m/min, but a project is afoot to increase the painting
speed even up to 100 to 150 m/min. In such a case, advantages to be
obtained by the application of the electrodepositing painting
method will be increased, but trouble as above-mentioned will
become acute.
That is, with a speed up of the painting speed, electrodepositing
conditions become more severe, particularly, a greater voltage and
electric current will be required. For instance, when carrying out
an electrodeposition with a painting speed of about 60 m/min. a
voltage of about 50 V for 4 seconds, an electric current of 2,000 A
will be required for 5 dm.sup.2 and 3 foot width.
As a greater electric current and voltage are thus required as the
result of the speed up of the painting speed, the electric behavior
of the coat formed by the pretreatment as a foundation for the
electrodepositing painting exerts a great influence on the
electrodepositing painting. That is, with an increase in the
resistance of the coat formed by a phosphate treatment or chromate
treatment the phenomena of arc spots occurring and the conductor
roll melting out become remarkable. Further, there must be feared
the danger of the melting out of the conductor roll occurring by
the electrolysis due to the formation of an electrolytic cell
between the conductor roll and the metal sheet to be treated and
the occurrence of arc spots, if a rinsing water is on the material
subjected to the foundation treatment at the position of the
conductor roll where it is brought into contact with the strip coil
sheet. As the result of various investigations made minutely in
view of the facts as above-mentioned on the conditions for the
foundation treatment and electrodepositing painting to perform the
successive paintings, it has been confirmed that the following are
the requisite conditions for regularly manufacturing an
electrodepositing-painted metal sheet: that is, excessive agent
used for the foundation treatment and excessive rinsing water
should not be attached to the surface of the metal sheet to be
treated and the insulation resistance of the coat formed by the
foundation treatment should be less than 100.OMEGA. cm.sup.2,
desirably less than 5.OMEGA. cm.sup.2 at the surface coming into
contact with the conductor roll.
Thus, the features of the first additional step can be concluded as
follows: the insulation resistance is kept at less than 10.OMEGA.
cm.sup.2, advantageously less than 5.OMEGA. cm.sup.2 at the surface
coming into contact with the conductor roll, and the coat to be
formed by the foundation treatment is properly regulated in its
quality, thickness and water content so that the above-mentioned
condition of the insulation resistance may be fulfilled, and then a
metal sheet, for instance, a galvanized steel sheet, which has been
subjected to the foundation treatment in the controlled manner as
above-mentioned, is sufficiently rinsed so that excessive agent
used for the foundation treatment does not remain on the treated
surface of the metal, and thereupon fully dried by wind or hot wind
before the metal is subjected to the electrodepositing painting
through the conductor roll to form an undercoat, on the treated
surface of the metal.
The second additional step of the present invention is as
follows:
In the successive painting of a strip steel sheet plated with zinc
or zinc alloy according to the method of the present invention the
steel sheet coated with a zinc layer or zinc alloy layer is
subjected to a phosphate treatment or other chemical-synthetic
treatment or other coat treatment which has a high electric
resistance, or not subjected to the above-mentioned treatment,
prior to the electrophoretic treatment with a water-soluble paint,
the second additional step is characterized in that the supply of
electricity should be so regulated that a contact rolling pressure
given by the conductor roll on the surface of the galvanized steel
sheet or chemical-synthetically treated galvanized steel sheet is
more than about 100 kg per 1 meter width of the steel sheet.
In the case of electrodepositing painting, particularly anodic
electrodepositing painting, it differs from a general metal plating
by the following two points: that is, an anodizing and a high
treating voltage. Consequently, in this case, special consideration
is to be given to the conductor roll, through which electricity is
supplied for the electrodepositing painting of a steel coil. If the
rolling pressure between the metal sheet to be treated and the
conductor roll is low, there occurs an arc between them, and if
water and the like are on the surface of the metal sheet, an
electrolytic cell is formed between the conductor roll and the
metal sheet, in which the conductor roll acts as the anode, while
the metal sheet as the cathode, whereby the melting out of the
conductor roll metal occurs. The occurrence of arc between the
conductor roll and the strip coil, which is usually galvanized and
then subjected to the phosphate treatment, causes not only a
melting out of the conductor roll as above-mentioned, but also a
sticking of zinc oxide on the surface of the roll and a damage due
to the sticking on the surface of the strip coil formed by the
chemical-synthetic treatment.
The second additional step of the present invention is to eliminate
various troubles connected with the occurrence of an arc, which
proves a hindrance to the electrodepositing painting. To obtain the
above-mentioned object of the second additional step, for instance,
in carrying out the electrodepositing painting of a metal coil,
this metal coil is pressed on the conductor roll at the upper part,
the side part and the middle part of the latter by using a pressing
roll or others. In this case, the rolling pressure should be about
100 kg, preferably above 300 kg per one meter width of the coil. In
this case, of course, a pressing roll for imparting the necessary
pressure is not limited to only one roll. A plurality of rolls may
be used, as occasion demands. The pressing roll may be replaced by
an imposition of a tensile force on the coil.
The third additional step of the present invention is as
follows:
In the successive painting of a strip steel sheet plated with zinc
or zinc alloy according to the method of the present invention, the
metal sheet coated with a zinc layer or zinc alloy is subjected to
a phosphate treatment or other chemical-synthetic treatment or
other coat treatment which has a high electric resistance, prior to
the electrophoretic painting with a water-soluble paint, this
additional step is characterized in that electricity is supplied
while arranging the surface of the conductor roll, which is to be
brought into contact with the steel sheet, by removing a melt stuck
to the said surface of the conductor roll, which is mainly composed
of zinc or zinc oxide, by means of a scraper such as a doctor
blade, immediately after the melt has stuck when supplying the
electricity.
The state of contact of the conductor roll with the strip coil will
be deteriorated, as the line speed increases. In this case, if an
electric resisting coat is formed on the surface of the strip coil
in advance, to which electricity is supplied, the production of
sparks between the strip coil and the conductor roll increases,
whereby there occurs the trouble of the conductor roll melting
out.
Particularly, in the case, when the strip coil is plated with a
metal such as zinc, which has a relatively small surface hardness
and a low melting point, and moreover a coat of high electric
insulation resistance is formed on the plated surface by a
phosphate treatment, or a chromate treatment or other resinous coat
forming, there are easily caused a trouble that the plating metal
is oxidized and burnt by sparks or is stuck to the surface of the
conductor roll, whereby the plated metal layer on the surface of
the strip coil is damaged.
As a result of investigations it has been confirmed that the melt
stuck to the surface of the conductor roll can easily be removed
from the conductor roll, so far as it remains still in the soft
state immediately after it has stuck to the conductor roll, but
with the lapse of time, it becomes harder and difficult to remove,
resulting in the formation of an increasing projection of the melt
stuck on the surface of the conductor roll, because of a new one
being successively accumulated after another. If the melt stuck on
the surface of the conductor roll is not prevented without delay
from being formed into a projection, not only damages caused on the
surface of the strip coil will extend in a wider range as well as
become heavier, the production of sparks will be accelerated,
whereby the loss of the conductor roll caused by the melting will
be hastened and the life of the conductor roll will remarkably be
shortened, but also the production of sufficient products will be
hindered.
The third additional step of the present invention is to eliminate
the above-mentioned disadvantages by using a very simple means.
That is, this step is characterized in that, when carrying out an
electrophoretic painting or other electric re-coating treatment of
a plated metal sheet having an electric resisting coat on its
surface, while pressing the conductor roll on the conductor roll,
the solidified melt stuck on the surface on the conductor roll when
supplying electricity is quickly and continuously scraped off by
means of a doctor blade made of, for instance, stainless steel or
other metal. If the doctor blade is positioned at a region of the
surface of the conductor roll which is not brought into contact
with the strip coil (for instance, a zinc-plated steel sheet, which
is further subjected to a phosphate treatment), while facing the
edge of the blade at a proper angle (.alpha.), that is, about
10.degree. to 20.degree. to the normal of the conductor roll, then
the solidified melt such as zinc oxide spottedly stuck on the
surface of the conductor roll can easily and effectively be scraped
off by the edge of the doctor blade, while the conductor roll is
rotated, consequently a painted steel sheet having a favorable
surface condition is obtained, as the electrophoretic painting can
thereby be applied on the steel sheet, as it is.
At the same time also the loss of the conductor roll by melting and
other disadvantages as above-mentioned can effectively be
reduced.
Further, in order to suppress an increasing production of sparks
between the strip coil and the conductor roll, which is caused by
the supply of a greater electric current as a result of the line
speed being increased, and which causes the loss of the conductor
roll by melting, resulting in a remarkable shortening of the life
of the conductor roll, the following countermeasure is to be taken,
such as forming the edge part of the conductor roll with an
electric insulating material by providing the edge part of the main
body of the conductor roll itself with a rubber or plastic lining
layer, so that the width of the surface of the conductor roll, to
which an electric current is supplied, may be made narrower than
that of the strip coil (for instance, a zinc-plate steel sheet
having a coat formed by a phosphate treatment or other
electric-insulating coat), advantageously, the former is made 0.9
times as wide as the latter, thereby to eliminate the part of the
surface of the conductor roll, where sparks are most produced.
Examples of the present invention are explained in the following:
##SPC1##
The result of paint-coating tests made about the above-mentioned
examples will be compared with conventional paint-coating methods.
##SPC2##
Next, a treating bath for electrophoresis adopted by the present
invention and examples of using the said bath will be explained in
Examples 2 and 3.
EXAMPLE 2
A galvanized steel sheet having a clean surface was made the anode,
while a stainless sheet was used for the cathode. A coat was formed
with an interpolar voltage of 80 V in the treating solution of the
composition as shown in the following:
Treating bath: Copolymer of ammonium acrylate and butyl ester
acrylate (ratio of polymerization 3/7 10 parts Ammonium chromate
0.2 part Water 90 parts pH 7.5 Anodizing chromate: 90 volts 30
seconds After rinsing baking for one minute at 250.degree. C
the thus obtained paint coat is a transparent one having a slightly
yellow-colored luster and shows no change for 250 hours in a salt
water spray test.
When an anodic electrophoretic treatment is carried out in the
treating solution of the present invention, an insoluble
electrodeposited coat is formed on the surface of a galvanized
steel sheet, which is proportioned to a time of supplying an
electric current, without resulting in a decrease of the electric
current and, then by drying the said coat by heating after a simple
rinsing or wringing a coat completely uniform and firm and
excellent in anticorrosiveness can be obtained.
The thus-obtained galvanized steel sheet which was subjected to an
electrodepositing treatment is practically used either as a steel
sheet having an undercoat as a foundation for a further painting or
an anticorrosive steel sheet itself according to more or less
amount of the deposit. Further, a colored paint coat may be formed
by causing an aqueous agent for dispersing coloring pigments
subjected to an anionic activator treatment to co-exist in the
treating bath of the present invention. This method is also
practically used as a surface treating method which answers the
purpose of effecting protection and decoration at the same
time.
By adding further sulfuric acid or boric acid to the treating bath
of the present invention, it becomes possible to remarkably improve
the throwing power of the coat formed and to impart marked and
useful properties thereto.
EXAMPLE 3
Treating bath: Copolymer of three kinds of compounds: methyl ester
methacrylate, ammonium acrylate and isobutyl ester acrylate (ratios
of copolymerization 3/3/4 ) 15 parts Zinc chromate 0 .25 parts
Methylated melamine 10 parts Water 75 parts pH 8 Anodizing
conditions: 60 volts 60 seconds After rinsing Baking for 2 minutes
at 200.degree. C
in this example there has been formed an electrodeposited coat
superior in atmospheric corrosion resistance and particularly in
corrosion resistance to that formed according to Example 2.
EXAMPLE 4
A galvanized steel sheet was used as a metal sheet to be coated
with paints. After brush-grinding by using a nylon series roll, the
steel sheet was subjected to a conventional zinc phosphate
treatment for 10 seconds at 50.degree. C. and then rinsed for 3 to
5 seconds, while buffing by means of a cotton buff. Then, it was
again rinsed for 2 to 3 seconds and thereafter wind-dried. Then,
the steel sheet was subjected to an electrodepositing coating with
paints, in which a water-soluble electrodepositing paint as
mentioned in Examples 2 and 3 was electrolytically deposited in an
amount of 30 to 40 mg/cm.sup.2. Immediately after wind-drying, the
sheet was coated with a final paint in the thickness of 15 to 20
microns. Thereupon the steel was fired at about 200.degree. C. for
50 to 60 seconds and coiled after water cooling.
Line speed 45 to 50 m/min Phosphate coat resistance 4 to 5 .OMEGA..
cm.sup.2 Electrodeposition current 40 to 5 V Time 3 to 5 seconds
Temperature 40 to 50.degree. C. Amount of deposition 30 to 40
mg/cm.sup.2 Final coating paint Acrylvinyl series, 15 to 20 microns
Salt water spray test excellent (for 500 hrs) Atmospheric corrosion
resistance excellent (for 6 months) Working adhesivesness Dupont 1
kg. 50cm excellent Erichsen 7mm excellent Bending 180.degree.
excellent
In this example there occurred neither arc spots nor loss of
conductor roll by melting during the process of electrodepositing
coating with paint.
EXAMPLE 5
A galvanized steel sheet subjected to a phosphate treatment was
coated with paint by the electrodeposition for the time of 3 to 5
seconds under the conditions of the line speed of 45 to 50 m/min,
40 to 50 V and 4 to 5 A/dm.sup.2, while a rolling pressure of 300
kg per 1 meter of coil width was imposed by means of one roll. The
electrodepositing paint was the water-soluble paint for use in the
electrodeposition as used in Examples 2 and 3. The bath temperature
was 40.degree. to 50.degree. C. The deposition amounted to 30 to 40
mg/dm.sup.2. The electrodeposition was followed by rinsing and
wind-drying. Without carrying out a baking, the steel sheet was
then coated with acrylvinyl series paint in the thickness of 15 to
25 microns and then baked at 140.degree. to 270.degree. C. for 50
to 60 seconds, and further rinsed again and coiled. After rinsing
the steel was coiled. In this example there was seen no occurrence
of arc spots and loss of conductor roll by melting. The properties
of the product were as follows:
Salt water spray resistance excellent (for 500 hrs) Moisture
resistance excellent (for 500 hrs) Atmospheric corrosion resistance
excellent (for 6months) Working adherence Dupont 1 kg.sup.. 50 cm
good - excellent Erichsen 7 mm excellent Bending 180.degree.
excellent
EXAMPLE 6
A galvanized steel sheet was used as a metal sheet to be painted.
After brush-grinding the steel sheet was subjected to a
conventional zinc phosphate treatment by using a commercial zinc
phosphate (at 70.degree. C. for 10 seconds). Then, the metal sheet
was pressed down on a conductor roll with a rolling pressure of 300
kg per one meter coil width by two rolls respectively. The
electrodepositing painting was carried out for 3 to 5 seconds under
the conditions of the line speed 45 to 50 m/min, 40 to 50 V, and 4
to 5 A/dm.sup.2. The electrodepositing paint was a water-soluble
acrylic acid series paint as used in Examples 2 and 3. The
electrodeposit amounted to 30 to 40 mg/dm.sup.2. Immediately after
rinsing and wind-drying the final coating was carried out with
acrylvinyl series paint and fired at a temperature of 140.degree.
to 270.degree. C. for 50 to 60 seconds. After water cooling, it was
coiled. There was found no occurrence of arc spots and loss of
conductor rolls by melting, and the product has the following
properties:
Salt water spray resistance excellent (for 500 hrs) Moisture
resistance excellent (for 500 hrs) Atmospheric corrosion resistnce
Excellent Working adhesiveness Dupont 1 kg.sup.. 50 cm excellent
Erichsen 7 mm excellent Bending 180.degree. excellent
EXAMPLE 7
In a coil painting of a hot-dip plated steel sheet, the steel sheet
was subjected to a zinc phosphate treatment at a temperature of
70.degree. C. for 10 seconds by using zinc phosphate, after the
brush-grinding. The electrodepositing paint composed of a copolymer
of ammonium acrylate and acrylic ester was electrodeposited in an
amount of 30 to 40 mg/dm.sup.2. After rinsing and wind-drying an
acrylvinyl series paint was painted in a thickness of 15 to 25
microns by using a roll coater and baked at 140.degree. to
270.degree. C. for 50 to 60 seconds. Then, the steel was
water-cooled and coiled. ##SPC3##
Thus even though the method of the present invention is a
two-coating and one-baking method, the paint does not come turbid
in its color, but shows an excellent adhesiveness and corrosion
resistance, because in the method of the present invention an
aqueous electrophoretic paint, which is essentially of the property
of being very easily dried, is used as an undercoating paint and
then a water-soluble or solvent-soluble paint is applied as a final
paint and thereupon is baked and dried for hardening. Moreover, as
the undercoat and the final coat, or more than two coats, as
occasion calls, may be baked simultaneously at one time, not only
there is required only one baking furnace but also the painting
line may be remarkably shortened in length. There are still further
advantages obtained by the method of the present invention that the
painting operation can easily be managed and thereby the yield of
products may highly be improved.
As is shown in examples as above-mentioned, the method of the
present invention can be applied not only to a successive painting
of a steel coil, but also to a successive painting of a cut steel
sheet.
* * * * *