Note: Descriptions are shown in the official language in which they were submitted.
-- 1 --
3-11780 +
Process for lacquer-coatin~ iron and steel
When applying liquid lacquers, especially aqueous
lacquer suspensions, a difficulty which arises, if the
electrophoresis process is not employed, during applic-
ation by the dipping or flooding process is that of
depositing the lacquer in a sufficiently thick layer and
without defects arising (i e.pore-free) in the region of
edges, corners, points and the like. This defective
covering of the edges is particularly pronounced in the
case of primer coating, i.e. when applying the first coat
of an anti-corrosion lacquer (of the primer), and in the
case of the lacquer-coating of iron and steel has dis-
astrous consequences in the form of increased corrosion
and rusting.
Attempts have already been made to solve the pro-
blem of the defective coating of the edges by adding
thixotropic agents to the lacquer and, especially in the
case of aqueous sys-tems, by relatively high concentrations
of emulsifier in the formulations. It is true that it
was possible slightly to improve the covering of the edges
in this way, but neither measure can be used for high
grade baking lacquers since both measures severely impair
the levelling of the lacquer applied.
The object of the invention is to find a process
for lacquer-coating iron and steel articles which does not
have the cited disadvantages of the known coating pro-
cesses. Application of the lacquer should be effec-
ted in a controlled manner, either uniformly or in a
manner which also enables the lacquer to be deposited in a
~k
26Z
thicker layer in the region of sharp edges and corners than
on the other surface parts of the article. By means of this
thicker layer, subsequent corrosion in the region of sharp
edges, which in itself is particularly susceptible to
corrosion, should be substantially excluded or reduced.
The invention relates to a process for coating iron
or steel articles with lacquers with improved uniform and
intensified deposition of the lacquer in the region of
edges, corners or points by dipping, flooding or spraying,
which comprises
a) using a lacquer which contains at least one ferromag-
netic pigment and
b) carrying out the coating in a magnetic field in such a
way that the edges, corners or points are located in the
region of increased magnetic flux 2 10 m T.
If de~lred, the lacquer may be used in addition t~
other conventlonal lacquer pigments and/or lacquer addi-
tiveC. According to the invention, the magnetic field of
an electromagnet is preferably used. Magnets which can be
used are not only those which have an iron core but also
coreless magnets, which, thus, are built up virtually cnly
of the magnet coils. In principle, permanent magnets are
also suitable if they meet the condition in respect of the
magnetic flux.
In general, for carrying out the process according to
the inventlon, the article to be coated is introduced into
the magnetic field and fastened. However, it is also pos-
sible to use a procedure in which the article to be coated
with lacquer is itself part of a magnet or, as a result of
close contact with a magnet, is virtually part of the magnet.
Suitable ferromagnetic pigments for the process accor-
ding to the invention are in particular the iron oxide
coloured pigments, such as black iron oxide, brown iron oxi-
de. However, nickel powder is also suitable.
According to the invention, the concentration of
-- 3 --
the ferromagnetic pigment in the lacquer employed is
between 5 and 70% by weight, based on the binder of the
particular lacquer; the binder is to be understood as
meaning the base resin, which can be mixed with the
corresponding curing agent. The lacquer can also
contain several ferromagnetic pigments at the same time.
The process according to the invention can be
used with virtually all lacquer-coa-ting methods and thus,
for example, also with powder-coating processes.
Preferably. however, it is used for those methods in
which liquid lacquers, especially aqueous systems, are
employed. The technical effect of the invention is
particularly pronounced when aqueous lacquer suspensions
are used. In principle, suitable lacquers are those
which contain thermoplastics as the base resins and also
those in which the base resins are curable synthetic
resins. Base resins based on thermoplastics are, for
example, saturated polyesters, PVC, polyvinyl propionate,
polyamides and polyacrylates. Curable synthetic resins
are in particular epoxide resins, phenol-formaldehyde
resins, urea-formaldehyde resins and melamine-formaldehyde
resins, and these can be combined with components necess-
ary for curing. Both the base resins based on thermo-
plastics and the base resins based on thermosetting syn-
thetic resins can also contain several resins of the
particular resin category at the same time.
The process according to the invention can be
used, for example, for the lacquer-coating, and especially
for the pri~ing with primers, of automobile bodies,
machines and equipment and parts thereof, and of steel
furniture. It is preferably used with the dipping
and flooding methods of application. In principle,
however, it can also be used for methods of application
which do not have any great industrial significance, for
example in spraying or in spreading by means of a brush.
The invention is illustrated in more detail with
the aid of the following examples.
_, . . ,.. . . . , ~ .. . . . . .
~ 2
Example l:
650 g of a solid bisphenol A epoxide resin (epox-
ide content = 0.6 mol/kg), 350 g of a saturated polyester
(acid number ab~ut 50, melting point about 95C), 650 g
of red iron oxide (BAYER, type 130 F) and 5 g of a flow
control agent (Modaflo ~, MONSANTO) are melted together in
a Co-kneader (BUSS AG, Switzerland) and, after cooling,
the mass is ground to a particle size of about lOO ~m
A suspension with a solids content of about 40% by weight
is prepared from this powder by adding water and this sus-
pension is then ground further in a bead mill to a
particle size of about lO ~m. After adding 50 g of
glycerine, a phosphated ("bonderised") steel sheet is
dippedir~othe suspension, the dip bath being provided with
an electromagnet as shown in Figure l. After a few
seconds, the metal sheet coated with lacquer is withdrawn
from the suspension and dried for lO minutes at room
temperature. It is then baked at 200C for lO minutes.
After baking, the metal sheet has a flawless, and in
particular pore-free, coating of lacquer on all edges and
surfaces.
Example 2:
The procedure of Example 1 is repeated except that
the magnetic poles are reversed (reversal of the direction
of current in the magnet coil). The result is
equally as good as in Example l.
Example 3: (comparison example)
The procedure of Example 1 is repeated except that
the dipping ~tion is carried out in the absence of the
artificial magnetic field (current switched off in the
magnet coil). The edges of the baked metal sheet ~re
exposed in parts and have many pores.
Exam~le 4:
A mixture of 600 g of a ~olid bisphenol A epoxide
resin ~epoxide content = l.O mol/kg), 5 g of "Uresin B"~
(flow control agent from Hoechst~, 300 g of benzoguanamine-
methylol methyl ether, 200 g of TiO2 and 300 g cf black
13,
iron oxide (BAYER, type 216 F) is processed, as in Example
1. to an aqueous suspension. After addîng 1.5 g of
amino coconut fatty acid oxethylate and 50 g of polypropy-
lene glycol to the 40% suspension, the formulation thus
formed is used in the following way to coat a deep-drawn
tin-plate mug.
A bar magnet is placed centrally on the base of
the mug, as shown in Figure 2, with the south pole facing
upwards, so that the north pole adheres firmly to the
base of the mug and the latter virtually becomes part of
a larger composite magnet. The mug connected to the
magnet is now inclined (as can be seen from Figure 2) and
lowered into thelacquer suspension. The entire
article is rotated about the longitudinal axis of the
magnet, so that the mug is coated with lacquer by the
dippingmethod exceptfor a central region, which is not
intended to be lacquer-coated. This procedure is
followed by drying and baking in the manner described in
Example 1. A uniform film with pore-free coverage of
the edges results.
Example 5: (comparison example)
The procedure of Example 4 is repeated except that
the iron oxide pigment is replaced by the same amount of
TiO2. The resulting lacquer film is in the main like-
wise uniform. However, the edges of the test metal
sheet are exposed in parts and have many pores.
Example 6:
A direct current source is applied to two coils
Ml and M2 in accordance with Figure 3 7 in such a way that
an electric current flows in the same direction through
both coils. A dip bath is placed in the magnetic
field which forms between the coils and this bath is
filled with a coating formulation according to Example 1.
A test metal sheet (P) made of steel is lowered into the
dip bath and raised again. After customary pre-
drying and baking of the coating, the metal sheet shows
flawless and in particular pore-free coverage of all
321~Z
-- 6 --
edges and surfaces with lacquer.
Ex~mple 7: -
The same experiment is carried out using anelectrical alternating voltage and this leads to the same
result.
