Note: Descriptions are shown in the official language in which they were submitted.
The present invention relates to producing a
pre-painted steel sheet at low production cost by combin-
ing metal coating and paint coating steps in one produc-
tion line.
In recent years, not only in the field of con-
struction materials but also in the fields of automobiles,
electric appliances, steel furniture and containers, there
has been an increasing tendency that cold rolled steel
sheets are replaced by metal coated steel sheets and
further by paint coated steel sheets. Particularly in
the applications where the steel sheets are paint coated,
there are various public pollution problems caused by the
paint coating process, and most users of paint coated
steel sheets are more and more inclined to switch over
~rom performance of paint coatings at their own shops to
procurement of already paint coated steel sheets (pre-
painted steel sheets).
Xowever, there exists one hindxous factor
against this ten~ency. 'hat is the high production cost
of the pre-painted steel sheets. This is more prominent
and serious in the case of production of pre-painted
steel sheets ~sing metal coated steel sheets as sub-
strates.
Thus, ~or production of pre-painted steel sheet
by using metal coated steel sheets as substrates, it has
been a conventional practice to electroplate a cold rolled
steel sheet as a substrate in a continuous steel coil
electroplating line to obtain a metal coated steel coil,
and this metal coated coil is paint coated, cured in a
separate coil paint coating line to obtain a pre-painted
steel sheet coil. There~ore at least two separate pro-
duction lines, electroplating line and paint coating
line are required in the conventional production o~ pr~-
painted steel sheets.
Therefore, one of the objects of the present
inven-tion is to provide a process for producing pre-
painted steel sheets in which the metal coating (plating)
and the paint coating, which have been continuously per-
formed in separate production lines, are performed in thesame production line, namely an in-line coating process.
By performing the metal coating and the paint
coating in the same production line, various wastes of
labour and time required by the conventional arts of
passing the steel coil throuyh separate two production
lines can be sa~ed, Specifically, transportation of the
steel coil between the two lines, packing of the steel
coil for prevention of rust during intermediate storage,
repetition of coiling and uncoiling, and material loss
caused by cutting the leading and rear ends of the coil
required for jointing or division of the steel coil can
be eliminated by successively performing the metal coat-
ing and the paint coating in the same production line.
However, there are various problems to be solved
in performing the metal coating and the paint coating in
the same production line.
As the metal coated steel sheets used for pro-
duction of pre-painted steel sheets, zinc coated sheets,
zinc alloy coated sheets, tin coated sheets, tin-free
steel sheets, aluminwm and aluminum alloy coated sheets,
and nickel coated sheets and so on are used, which all
can be produced by an electroplating or hot-dip coating
process. These metal coated sheets which are used with-
out further treatments in wide applications other than
as substrates for the pre-painted sheets are produced in
a great amount. Therefore, the metal coating process
must be adapted for the mass production at low cost,
reaching a production rate as high as more than lO,000
ton per month in one production line,
On the other hand, demands for the pre-palnted
sheets are rather small as compared with the production
of metal coated sheets, although production of pre-
painted sheets has been increasing, so that it is not
necessary to paint coat the whole of the met~l coated
sheets produced in one production line, but rather it is
necessary to manage so as to obtain a certain amount
of pre-painted sheets and a certain amount of metal
coated sheets in one production line~ Further, it is
necessary to select paints to be coated on the metal
coated sheets depending on the final applications of the
pre-painted sheets, and it is most common to change the
curing conditions in view of the paints to be used.
However, the conventional axt of curing paint coated coils
which is most commonly practiced is nothing more than
the so-called hot blast curing method which comprises
blasting a high-temperature hot blast to cure the paint
by the heat transferred by the blast. According to this
hot blast curing method, it is possible to control the
curing condition on the basis of the final sheet temper-
ature, and the temperature of the hot blast is adjusted
so as to obtain an optimum temperature for the paint to
be coated, and the line speed is adjusted so as to control
the travelling time of the coil through the furnace.
2~ In connection with the ~bove conventional art,
there are various problems.
One problem is that it is necessary to stop the
line until the temperature o* the hot blast in the curing
furnace reaches a predetermined temperature or it is neces-
sary to wait until the furnace temperature lowers to sucha degree as that no adverse effect is produced on the
quality of metal coated substrates. This is particularly
necessary when the production is changed over in one pro-
duction line between the metal coated sheets and the pre-
painted sheets, more particularly when the production of
pre-painted sheets is started or when the production of
pre-painted sheets is terminated and changed over to the
production of metal coated sheets.
The waste time caused by the above change-over,
normally ranges from 30 minutes to one hour, and causes
the lowering of the production rate, hence increased pro
duction cost.
A second problem is caused when it is required
to change the final sheet coil temperature due to the
change of paints to be coated. In this case, it is
possible to obtain a predetermined final sheet coil
temperature by changing the line speed without changing
the furnace temperature in principle, but in many cases,
it is impossible to take such procedure in view of the
metal coating conditions or, if possible, such procedure
will lower the production efficiency. Explanations will
be made referring to the electroplating process. In
view of requirements for increasing the production as
high as possible, namely the production amount per unit
hour, the electroplating is performed by passing the
current up to the limi~s o~ the capacity of current
sources for rectifiers for the electroplating so that
the line speed is automatically determined by the sheet
widths of coils, the plating thicknesses and the capaci-
ties of rectifiers. Therefore, if the line speed is tobe determined from the curing condition of the paint
coating, the capacity of the rectifier is not sufficient
so that a re~uired plating thic]~ness cannot be obtained
or the operation is compelled to be done at a lower line
speed than the proper line speed.
For solving the second problem, it may be con-
templated to change the furnace temperature, but 10 to 30
minutes are wasted for the change of the furnace temper-
ature and the line must be stopped for this period o~
time.
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~62~5
A third problem is caused when the coil width,
sheet thickness or plating thickness are changed. Thus,
when the coil width or the plating thickness is to be
changed, it is re~uired to change the line speed due to
the limited capacity of the rectifier as mentioned in
connection with the second problem, so that the furnace
temperature must be changed accordingly, This change of
the furnace temperature requires 10 to 30 minutes during
which the production line must be stopped, thus, lowering
the productivity. Also when the coil thickness is to be
changed, it is necessary to change the furnace temperature
so as to assure to obtain a desired same final sheet
temperature even at the same line speed, or to change the
line speed at the same furnace temperature so as to ob-
tain the same final shee-t temperature. Therefore, similar
problems as above are caused.
The second ar,d third problems mentioned above
are confronted with also in the cases of metal coatings
by hot dipping in molten metal baths, in which the condi-
tions of pretreatments, such as oxidizing and ~he heattreatment in a reducing, depend on the sheet thickness
and width, and in some cases this situation cannot be
compatible with the situation ~here the paint curing
condition depends on the sheet thickness and the type
of paints to be coated.
The present inventors have made various investi-
gations and studies to solve the problems in the conven-
tional in-line coating art combining the metal coating
and the hot blast curing of paint coating, and have found
that a novel in-line coating art utilizing a curing system
by means of a near infrared radiation is very effective
and advantageous. According to this novel art, it is not
only possible to obtain immediately the same curing condi-
tion, namely the same final sheet temperature, despite
changes in the line speed, sheet thickness and width, but
~6235i
also it is completely unnecessary to stop the production
line at the time of change over from the metal coated
products to the pre-painted products or from the pre-
painted products to the metal coated productsO The
present invention has been co~pleted on the basis of the
above discovery.
According to the present invention, the curing
conditions can be optionally selected in accordance with
desired line speeds for metal coating, and it is possible
to perform or stop the paint coating and the curing at
any desired time, while the metal coating is continuously
performed without stopping the line. This is the second
feature of the present invention
A third feature of the present invention is
particularly important for production of one-side metal
coated or one-side paint coated steel sheets used as
rust-preventive materials for automobile
Thus, according to the present invention, a
chemical conversion treatment is intentionally applied
to the back side of the one-side coated sheet ox a thin
metal coating is applied to the back side at the time of
the coating-curing step so that rust and bluing are
effectively prevented
If the chemical conversion treatment is to be
~5 applied only to one side of the sheet, the paint coating
method is limited to a roll coating and the like, but if
the thin metal coating is applied and then, after the
chemical conversion treatment and the paint coating and
curing, the thin metal coating is mechanically removed,
3~ the chemical conversion ~ilm can be removed together with
the metal coating so that the non-paint coated surface
provides a fresh surface, on which users can advantageously
apply a phosphate treatment, for example.
When one-side metal coated steel sheets are used
as substrates and paint coatings are applied thereon, there
:~9i~2~5
is no means to remove the chemical conversion film adher-
ing on the steel sheet, and if this film is removed by
mechanical grinding, it is very difficult to do so as
compared with the present invention where the film is
removed all together with the metal coating, so that
users are confronted with troubles ~hen they apply
phosphate treatrnents.
According to the present invention, pre-painted
steel sheets and metal coated steel sheets are produced
in a production line comprising uncoilers, pretreatment
equipment, metal coating equipment, chemical conversion
treatment equipment (pre-treatments for paint coating),
paint coating equipment, near infrared radiation curing
e~uiprnent, coilers~ etc.
1~ According to one ernbodiment of the present
invention, steel coils may be used without cutting, and
according to another embodiment, cut sheet products can
be obtained by substituting the coilers with shears and
pliers. Also by substituting the uncoilers and coilers
respectively with cut sheet feeders, and cut sheet
pliers, constituting a cut sheet production line, the
present invention may be applied to cut sheets.
Metal coating equipment useable in the present
invention may be classified into two groups' electro-
2~ plating equipment and hot-dip metal coating equiprnent,
and appropriate pretreatrnent equipment are selected for
these metal coating processes. As for the types and
kinds of metal coatings, the present invention is not
limited to specific metal coatings and can be applied
to various metal coated sheets, such as zinc coated,
zinc alloy coated, tin coated, tin-free, alumini~n
coated, aluminum alloy coated and nickel coated steel
sheets. Also the pxesent invention is not limited to
specific metal coating processes.
As the pretreatments for paint coating, the
present inver.tion is not limited to specific pretreat~
ments, but any pretreatment useful for paint coating,
suc~ as phosphate treatment, chromate treatment,
passivation treatment (oxide film formation treatment)
can be used, and these treatments can be performed by
any suitable method, such as spraying, immersion, roll
coating and electrolysis.
The paint coating in the present invention
can be applied by various methods, such as roll coating,
spray coating, curtain flow coating, immersion coating,
and electrodeposition coating, but from the points of
uniformness and stability of the coating, the roll
coating is most preferable when sheet`coils are treated,
~5 and the curtain flow coating is most preferable when
the cut sheets are treated.
Further, the present invention is not limited
to specific types or kinds of paints, but various paints
such as thermal setting resins can be advantageously
selected depending on final applications~
The near infrared radiation lamp used in the
present inven~ion is a bar-shaped electric heating lamp
which emits a near infrared radiation having its energy
peak at a wave length o* 1 to 2 ~m, and characterized in
that the density of output energy is very high and the
time required for reaching the constant output is only
about one second. These characteristics cannot be ob-
tained by the conventional infrared lamp, far infrared lamp
or ultraviolet lamp. ~s commercially available near
infrared radiation lamps they are available from Nippon
Phillips Corporation, Research Inc., Shinku Ricoh Co.,
Ltd. in Japan.
The products obtained by the process according
to the present invention include pre-painted steel sheets
for indoor and outdoor building materials, pre-painted
8 --
~6Z~3~
sheets for working into containers, electric appliances
and furniture, pre-painted sheets for manufacturing of
various cans including food cans and other cans, and
pre-painted sheets for rus-t prevention purpose in auto-
mobile. mus, the products obtained by the presentinvention can be used in very wid~ applications requir-
ing different qualities.
The invention will now be described with
reference to the accompanying drawings which show a pre-
ferred form thereof and wherein:-
FIGURE 1 schematically shows a production linefor the present invention.
FIGURES 2 and 3, respectively, illustrate
arrangements of near infrared lamps,
in which si~ lamps constitute one
unit lamp house.
The present invention will be described in
more detail as applied to the production of pre-painted
sheets *or rust prevention in automobile by combining
zinc-alloy electroplating and weldable paint coating with
reference to Figure 1.
In Figure 1, a cold rolled steel sheet or a hot
rolled steel strip to be treated is mounted o~ an uncoiler
13 and the strip uncoiled therefrom is introduced to a
group of pretreatment equipments 1 - 4 through shears,
jointing machines and pliers (nGt shown).
m e pretreatment equipment comprise a de~reas-
ing tank 1, a washing tank ~ and an acid pickling tank,
a washing tank 4, in which the strip surface is washed
and activated by spraying, immersion, ~rushing or
electrolysis, whichever suitable as pretreatment for
the metal coating.
The principal object of the pretreatment is
to assure the adhesion of the metal coating on the sub-
strate, and the adhesion of coatings and corrosion
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~g~Z35
resistance of final products, and so far as this objectis achieved, the present invention is not limited to
specific methods and conventionally known additional
treatments other than the above treatments can be
applied without departing from the scope of the present
in~ention,
The steel strip after the pretreatment is led
to a plating tank 5 where it is applied with a desired
thickness of a desired metal coating appro,priate to the
final application, As for the metal coating useable in
the present invention includes zince coating and zinc-
alloy coating, such as zinc-nickel alloy coating, zinc-
nickel-cobalt alloy coating, zinc-nickel-~hrome alloy
coating and zinc-nickel-bron alloy coating. The present
invention is not limited to the above coatings and various
other metal and alloy coatings can be used.
Regarding the amount of metal coatings to be
applied to the strip, it may be selected depending on the
final applications and the desired corrosion resistance
of the final products, but in order to assure desired
effects of the metal coatings, it is desirable to apply
the metal coatings in amounts not less than 1 g/m , prefer-
ably not less than 3 gJm , and more preferably not less
than 5 g/m2 and in amounts not larger than 15 g/m2.
When the metal coatings are applied by electro-
plating, the electrolyte may be acid or alkaline and
there is no specific limitation. The metal coating is
performed in a suitable bath under suitable conditions
depending on the desired ~uality of the final products
and in view of the productivity. Further, the electro-
plating tank may be of any desired type and shape, such
as vertical and horizontal tanks, and the number of
electroplating tanks may be selected depending on the
desired production rate.
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~6~35
According to the present invention, two-side
paint coated products and one-side paint coated products
can be obtained. In the former case, the amounts of the
coatings on both sides may be selected depending on the
desired qualities In the latter case, only one side
on which the paint coating is to be ~pplied i5 metal
coated, or for the purpose of preventing rust formation
in the production line and temper color during the curing
a thin metal coating not larger than 3 g/m is applied
to one side of the strip on which the paint coating is
not to be applied, and this thin metal coating may be
or may not be chemically or mechanically removed immed-
iately before the coiling or during other suitable steps
to obtain a final product.
After the metal coating, the strip is washed
in the washing tank 6 and led to the chemical conversion
tank 7, where it is subjected to phosphate treatment,
chromate treatment, passivation treatment or other pre~
treatments.
The chemical conversion ma~ ba performed by any
conventionally known method, such as immersion, spraying
electrolysis, roll coatin~ and by means of reaction cells.
After the chemical conversion treatment, the strip is
washed and subjected to chrome-sealing (not shown), if
necessary, and led to a drying furnace 8u
Then the strip is applied with a weldable paint
coating in a paint coater 9. l'he coating may be performed
by spray coating, curtain coating, etc. although the roll
coating is most common.
~s the weldable paint, powder zinc paint is
known, but the following paint com~ositions are more suit~
able for the present invention:
~g6~3S
a) paint composition comprising a vehicle mainly
composed of resins such as epoxy, polyester,
acryl, vinyl, etc., not less than 8~/o by
weight (with respect to non-volatile matters)
of powdered zinc and optionally powdered
aluminum, magnesium and carbon,
b) mixed powder paint composition comprising a
vehicle mainly composed of resins such as
epoxy, polyester, acryl, vinyl, etc. at least
one of iron, nickel, chrome, cobalt, manganese
and their alloys in the powder form, and
powdered carbide of at least one of tita~ium,
zirconium, hafnium, vanadium, niobium, tantalum,
chrome, tungsten and their mixtures, not less
than 5% hy weight, preferably 40 to 80% by
weight of powdered zinc, and optionally a
small amount of at least one of powdered
aluminum, magnesium and carbon.
Naturally, the above paint compositions may
further comprise small amounts of rust preventive pig-
ment, coloring dye and pigment, and other additives within
a range which is not hinderous to the desired weldability~
The thickness of paint coatings may be determined
depending on the final applications and the re~uired
qualities, but normally it ranges from 3 to 20~, Although
the paint coating may be applied outside the above range
without departing from the scope of the present invention,
paint coatings less than 3~ are generally insufficient
for assuring the desired corrosion resistance of the
paint coating, and paint coatings beyond 20~ generally
tend to deteriorata the weldability.
The zinc powder contained in the paint composi-
tion synergetically functions with the metal coating su~-
layer and selfsacrifyingly prevents the corrosion of
the base steel sheet~ For this purpose and in view of
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3.~L9~235
the weldability, at least 80% by weight of zinc powder is
required in the zinc-powd~r-straight paint composition. In
the case of the mixed powder paint composition, at least
5% by weight, preferably at least 4~/O by weight of zinc
powder is added for the purpose of assuring the desired
corrosion resistance. The upper limit is determined
mainly from the point of workability, but greatly
influenced by the kind and amount of other powder
additives to be added together the zinc powder. There-
fore, the upper limit of 80% serves merely as astandard.
In the curing furnace 10, the near infrared
lamps are arranged above and below the strip. The
arrangement of the lamps may be done in a prallel direc-
tion to the running direction of the strip (Figure 3),or in a perpendicular direction to the running direction
of the strip (Figure 2)~ In the latter arrangement, as
the energy density at the socket portions 16 and 17 of
the lamp 15 lowers, it is desirable to arrange the lamps
in a zig-zag manner. In the former arrangement in which
the lamps are arranged in the parallel direction, to the
line direction, and the low energy zone of the socket
portions 16 and 17 is distributed uniformly in the width
direction, the pro~lem is much less. Normally, 4 to 8
lamps constitute a unit of lamps, and these units of
lamps are arranged in the lamp house provided with a
reflection plate. The reflection plate is desirably in
such a shape as that the energy density of the lamp house
in the width direction is maintained to be almost uniform,
Regarding wirings for the lamps, one independent
wiring is provided for each unit of lamps or each lamp so
as to turn on only the required number of lamps in
accordance with the line speed, the sheet thickness and
width. This operation can be automatically controlled ~y
means of a process computer and the like by measuring the
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Z3~;
sheet thickness, width and the line speed or by inputting
necessary informations. Against possible damage or dis-
order of the lamps, auxiliary lamps may be provided and
automatically turned on by detection of the damage or
disorder.
The strip cured under predetermined conditions
in the curing furnace 10 is cooled in air and water,
dried in the dryer 12, ground in a one-side grinding
machine, if necessary, cut by a shear, looped by a looper,
oiled by an oil coater, etc~ (not shown) and finally
coiled on the coiler 14 to obtain coil products, or it
is cut into predetermined lengths and piled to obtain
cut sheat products.
In order to promote the evaporation cf the
solvent in the paint coating prior to the irradiation
by the near infrared lamp~, a near infrared furnace or
the like may be arranged.
The present invention will be more clearly
understood from the following embodiments.
EXAMPLE 1:
A cold rolled steel sheet coil of 0.7 mm thick
and 1000mm width is applied with zinc coating by electro-
plating, and coated with a zinc-base paint in the
apparatus as shown in Figure 1. Ihe electropla-ting tank
is a horiæontal type with a total effective length of
19 m (1.5 m x 16) using an electroplating bath contain-
ing 400 g/~ zinc sulfate, 25 g/~ ammonium sulfate with
pH at 1Ø The zinc-base paint composed of 85% zinc
powder and epoxy resin (Epicote OL-55) is applied in
l0~ by a roll coater.
As shown in Figure 3, 42 near infrared lamps
of 2 kw/30 cm (made by Nippon Phillips CorpO) are
arranged above and below the strip in the parallel
direction of the line and similar 30 lamps are arranged
above and below the strip in the width direction of the
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23~
line at intervals of S cm. The lamps are spaced 5 cm
from the strip. The zinc coating is applied on the strip
to an amount of 20 g/m at a current density of 50 A/dm
which is the upper limit of the capacity of the rectifier
for the electroplating. The line speed is 90 m/min.
The curing is performed by the near infrared lamps in
such a manner that only 25 lamps in the width direction
which corresponds to the strip width are turned on and
only 25 lamps in the line direction are turned on to
obtain a strip temperature of 260C, and the qualities
of the resultant paint coated sheets are shown in
Table lA.
Then in order to increase the zinc coating to
40 g~m , the line speed is changed to 45 m/min. and the
electroplating is performed at 50 A~dm . Along this, only
12 lamps in the line direction are turned on to obtain a
strip temperature of 255C without stopping the line.
This strip temperature is almost same as that obtained
in the case of the zinc coating of ~0 g~m . The resul-
tant qualities are shown in Ta~le lB.
Further, the zinc coating is changed to 10 g~mIn this case, the capacity of the rectifier is well
sufficient as contrary to the case of 40 g/m zinc coat-
ing so that the line speed is increased to its upper
limit of 150 m/min, and the electroplating is performed
at 30 A/dm . Along this, 42 larnps in the line direction
are turned on to obtain a strip temperature of 260C
without stopping the line. This strip temperature is
almost same as that obtained at 20 g/m2 zinc coating,
and the qualities of the resultant products are shown
in Table lC.
EXAMPLE 2:
Using the similar apparatus as used in
Example 1, a steel strip of 0.7 mm x 1000 r~m is applied
with a zinc coating of 20 g/m2 and with a weldable paint
- 15 ~
~ lL9~;~3S
coating (same as in Example 1) of 10~ and cured by means
of near infrared lamps~
Then a steel coil of 0.5 mm thick and 1000 mm
wide is welded to the above coil for the purpose of
producing coated sheets with 20 g/m zinc coating and
10~ paint coating under the same electroplating condltion.
In this case, however, only 18 infrared lamps in the line
direction ar~ turned on for curing the paint coating to
obtain a final strip temperature of 260C as desired
without stopping the line, and the qualities of the
resultant products are shown in Table lD~
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