Deflecting device for viscous coating material freely flowing in the form of a sheet

A deflecting device includes a deflecting electrode (13), which is disposed at a spacing below a lip nozzle (11.1), from which the viscous coating material (10.2, 10.1) flowing freely in the form of a sheet is emerging, and which extends over the entire width of the coating material sheet. This deflecting electrode includes an electrode arrangement (31), the exposure region of which facing the sheet surface is subdivided into a number of electrode elements (33) which taper outwardly to a point. When placed under a voltage, the electrode arrangement (31) provides an ion stream directed towards the surface of the coating material sheet. The impact of this ion stream on the surface of the coating material sheet (10.2) imparts to the latter a change in direction (.alpha.) towards the deflecting electrode (13), so that a flat substrate (5.1) running horizontally towards the deflected coating material sheet (10.1) impinges on the sheet (10.1) at an acute angle (.beta.). The impact of the substrate (5.1) on the sheet (10.1) at an acute angle causes a smooth, undulation-free application of the coating material to the substrate surface.

The present invention relates to a deflecting device for viscous coating 
material freely flowing in the form of a sheet. 
It is known to employ a so-called lacquer casting machine for the 
application of liquid (viscous) coating material to flat, horizontal 
surfaces of a substrate. The principal area of application of such 
machines is the coating of flat plates of wood, metal, plastic material 
etc., which are designed in formats with practically any, but preferably 
rectangular outline shapes. The problem giving rise to the invention is to 
be set forth with reference to plate-shaped substrate bodies, hereinafter 
simply referred to as plates. 
The plates are fed on a horizontal transport web, e.g. a conveyor belt, to 
a processing station, at which they are moved past under a casting head 
emitting the viscous coating material in the form of a liquid sheet of 
calibrated thickness. Such a machine is designed for continuous operation, 
the liquid sheet flowing without interruption practically vertically 
downwards in the direction of a collecting container, in which coating 
material not used for a coating process is collected and returned to the 
casting head by means of a pump. A spacing is preferably maintained 
between two successive plates, so that the coating can commence precisely 
at the leading edge and terminate at the trailing edge, and no bridges of 
coating material are formed between adjacent plates. 
Since the plates having a thickness of preferably 10-40 mm are provided 
with leading and trailing surfaces standing perpendicular to the plate 
surface and pass through at a speed of approximately 50 m/min under the 
casting head, there is a danger that the coating material sheet, which has 
a thickness of approximately 3/100 mm to approximately 6/100 mm and which 
likewise falls substantially vertically, will start to oscillate or 
flutter as a result of the pressure of the air which has built up at the 
plate on the inlet side and the vacuum on the outlet side. As a result of 
the instability on the inlet side, which is predominantly due to the air 
pressure head, there is produced at the coating material sheet a wave-like 
cross-sectional shape, which results in surface irregularities in the 
coating in the inlet region of the plate. Since a smoothing operation at 
the still liquid coating material is as good as ruled out, costly further 
processing must be provided for in order to achieve a clean edge region. 
The vacuum on the outlet side does indeed have no disadvantageous 
consequences as regards the appearance of the coating; however, it 
increases the difficulty of separating the sheet at the end of the coated 
plate and promotes the formation of a standing wave at the coating 
material sheet, which now stands opposite the following plate. 
Experiments have shown that the corrugation of the coating material sheet 
on the inlet side of the plate to be coated can be caused virtually to 
disappear if an acute angle is maintained between the plate surface and 
the sheet surface in the directions of movement of the plate and of the 
sheet. It is assumed that as a result of this measure the build-up of an 
air pressure zone at the plate inlet side is prevented, since the air 
forming a pressure head can freely flow away in a downward direction from 
the wedge-shaped space formed in front of the plate inlet side. The 
initial contact of the flattened-out sheet surface with the plate surface 
thus takes place "softly". The subsequent coating of the plate surface by 
the coating material sheet, which is already inclined in the direction of 
movement of the plate, can take place without a large change of direction 
in the sheet material. 
On reaching the trailing edge of the plate, the suction effect acts at the 
reverse side of the plate in such a manner that the sheet is drawn by 
suction to the plate edge and, as the plate continues to move, is directly 
pulled off below the edge. It is to be assumed that as a result of the 
separation of the sheet below the plate edge, the progress of the sheet 
remains stable and the leading edge of the subsequent plate runs on to a 
flat sheet surface. 
However, the problem consists in deflecting a coating material sheet in a 
selfsupporting manner at an acute angle to a flat substrate surface, while 
maintaining horizontal delivery of the substrates to be coated or of the 
said plates on a transport arrangement. In this connection, it must be 
borne in mind that on the one hand the use of a horizontally running 
transport arrangement offers substantial operational advantages as 
compared with such an arrangement with rising and/or falling sections of 
movement, and that on the other hand, however, a liquid sheet flowing down 
from a casting head can only flow away vertically on a natural path, for 
physical reasons. A possibility for the non-contact deflection of a liquid 
sheet which has a thickness of only 3-6 hundredths of a millimeter 
consists in directing air currents towards the sheet surface below the 
casting head in such a manner that the sheet alters its direction of 
motion in the desired manner. Quite apart from the fact that it is 
extremely difficult to generate sufficiently stable surface currents, 
which ensure the guiding of the sheet in a flat configuration, such air 
curtains have the tendency to alter the liquid surface, e.g. to oxidize it 
and/or to dry it out. A disadvantage would in particular be a reduced 
adhesion capacity on the substrate body or the plate surfaces. 
The object of the invention accordingly consists in proposing a deflecting 
device for viscous coating material flowing freely in the form of a sheet, 
with which device the abovementioned problem can be reliably solved in a 
simple manner.

The lacquer casting machine shown schematically in FIG. 1 includes, within 
a machine frame 1, a deliveryside (first) conveyor arrangement 2, and an 
exit-side (second) conveyor arrangement 3, which are separated from one 
another by a so-called casting gap 4, which will be explained later. The 
conveyor arrangements 2 and 3 are preferably longitudinally arranged, 
synchronously running transport belts, which ensure stable guiding of the 
substrates 5.1, 5.2 and 5.3 to be coated through the machine. The minimum 
width of the casting gap 4 is given both by the length of the substrates 
5.1, 5.2 etc. and also by the design and the mode of operation of a 
coating arrangement designed generally by 6, and can be designed to be 
narrower or wider by a decrease or an increase in the relative spacing of 
the conveyor arrangements 2, 3. 
The coating arrangement 6 consists essentially of a schematically shown 
casting head 7, a deflecting device 9, according to the invention, for a 
coating material sheet 10.1, and a collecting arrangement 8 for coating 
material not applied to substrates 5.1, 5.2 etc. The casting head 7 of a 
known embodiment comprises essentially a storage container 7.1 to receive 
liquid single-component or multi-component coating starting material 10 
with a high dielectric constant and a longitudinal flat nozzle 11 at the 
floor of the storage container 7.1. The longitudinal dimension of its 
casting lips 11.1 is coordinated with the coating width at the substrates 
5.1, 5.2 etc., and its width of transmission can be set by means of a 
calibration device 12 to the desired thickness of the coating material 
sheet 10.1. This thickness is usually within the range from 0.02 to 0.08 
mm. The speed at which the sheet flows out from the flat nozzle 11 and the 
surface stability depend essentially upon the viscosity of the coating 
starting material. The prerequisite is a closed-surface, uniform and flat 
flow emerging from the flat nozzle 11, with theformation of a sheet 
section 10.2 flowing in the first instance vertically downwardly along a 
path of travel. 
By means of a deflecting electrode 13 which will be described later, there 
can be imparted to the coating material sheet 10.1 by an ion stream 
emerging from the deflecting electrode 13 a deflecting effect, as a result 
of which the sheet 10.1 experiences a path inclination .alpha. towards the 
electrode 13 from the ion impact zone on its surface onwards. This path 
inclination can be adjusted by application to the electrode 13 of a 
voltage adapted to the desired angle of inclination. Expediently, the path 
inclination .alpha. is selected in such a manner that the coating material 
sheet 10.1 does indeed pass as close as possible to the inner deflecting 
region 3.1 of the exit-side (second) conveyor arrangement 3, but is not 
drawn onto the latter. Such a danger exists in consequence of the 
ionization of the surface of the sheet 10.1 on the electrode side. When, 
as shown, no substrate (e.g. 5.1) bridges the casting gap 4, the sheet 
10.1 passes in an oblique position through the gap 4 towards a first 
collecting flap 14, the inclination angle .alpha. of which can be adjusted 
(double arrow 14.1). In this connection, it is important that the sheet 
10.1 impinges on the flap 14 in such a manner that the coating material 
flowing forward can flow away from the flap surface into a collecting 
trough 15 without any tendency to building up a pressure head. As a result 
of this, the creation of undulating and fluttering of movements at the 
lower end of the sheet 10.1 can effectively be counteracted. 
When the deflecting electrode 13 is switched off, the coating material 
sheet 10.3 flows according to the broken line in a vertical direction 
directly in front of the inner deflecting region 2.1 of the delivery-side 
(first) conveyor arrangement 2 to a second collecting flap 16 in the 
collecting trough 15. Just like the first collecting flap 14, this flap is 
also expediently inclined in such a manner that the coating material sheet 
10.3 freely flowing down flows away from the flap surface into the 
collecting trough 15 without any tendency to build up a pressure head. A 
return pump 17 returns the coating material which has collected in the 
collecting trough 15 to the trough 7.1 of the casting head 7 at 
appropriate time intervals via a pipe 18. 
When the lacquer casting machine according to FIG. 1 is set into operation, 
in the first instance the coating material sheet (partial sections 10.2, 
10.3) is brought out of the casting head 7 by setting of the flat nozzle 
11 to the desired thickness of 0.03 to 0.06 mm and uniform outflow. At 
this stage, the sheet runs in a substantially vertically downward 
direction (broken line 10.3). Following this, the deflecting electrode 13 
is aligned by adjustment of its supporting device 19 and is acted upon, by 
application of a high voltage, by a potential which is capable of causing 
a deflection of the sheet section 10.1 below the electrode 13 through an 
acute angle .alpha.. When the delivery-side and exit-side conveyor 
arrangements 2 and 3 have been set into operation, in the first instance a 
first substrate, in FIG. 1 the plate 5.1, is guided into the casting gap 4 
and conducted at a speed of 40-60 m/min in the direction of the arrow A 
through the casting gap 4, so that the surface of the plate 5.1 is covered 
with a coating of coating material. 
The coating process which results in this connection is schematically 
represented in FIG. 1a, in its individual Phases I to IV. As soon as the 
leading edge 5.1' runs up to the sheet 10.1 approaching at the angle 
.beta.=90.degree. -.alpha. (Phase I), the latter breaks away along this 
edge. The edge 5.1' is expediently of a sharp configuration, in order to 
achieve a defined line of breakage 21. As a result of the air pressure 
head 22 prevailing below the line of breakage 21, the sheet section 10.1', 
which is downwardly oriented and which falls rapidly in a downward 
direction, is pressed to some extent at its upper end away from the end 
surface of the plate 5.1 (broken lines), so that coating of the end 
surface and thus undesired further processing are avoided. 
The speed of forward movement of the plate 5.1 and the rate of flow of the 
coating material sheet must be coordinated with one another in such a 
manner that the sheet is slightly stretched when applied to the plate 
surface, in order to achieve a clean coating 23. The result of this is 
that the initial angle of approach .beta. decreases slightly to .beta.' in 
the course of the coating operation (Phase II), i.e. the sheet 10.1 runs 
ahead in a somewhat flatter configuration in the course of coating. This 
condition persists until the plate trailing edge 21' is reached (Phase 
III). At this point, supported by a trailing edge vacuum, the sheet 10.1 
breaks off and, in consequence of the now free access of air, returns 
again according to arrow 24 to its original inclination .beta. (Phase IV), 
without coating the plate trailing side 5.1". In this connection, cf. also 
the plate 5.3 in FIG. 1 on the conveyor arrangement 3. 
In the event that the coating material sheet 10.1 cannot be sufficiently 
deflected by a single deflecting electrode 13, a deflecting arrangement 9' 
with two (or more) deflecting electrodes 13', 13" can be used according to 
FIG. 1b. The reference numerals provided with a superscript designate 
components which are identical with those evident from FIG. 1. In 
principle, the casting head 7' can be constructed in the same manner as 
that according to FIG. 1. In the same way, the two deflecting electrodes 
13', 13" can be designed in the same manner or indeed in a different 
manner. The web inclination changes .alpha.' and .alpha." caused by the 
two deflecting electrodes 13', 13" are adjusted in a manner similar to the 
procedure described with reference to FIG. 1. The two deflecting 
electrodes 13', 13" are constructed on supporting devices 19', the 
positions of which can be changed and which, in association with an 
adaptation of the electrode potentials, permit adjustment of the desired 
change in path inclination in sections. On flowing out in spaces between 
substrates, as is also shown with reference to FIG. 1, the coating 
material sheet 10.1' impinges again on the collecting flap 14' at an acute 
angle, in order to avoid backwash while flowing out. 
Two examples of the construction of the deflecting electrode 13 or 13', 13" 
are evident from FIGS. 2 to 5. In both embodiments, an electrode 
arrangement generally designated by 31 or 31' is situated within the 
cavity of an elongate, essentially U-shaped profiled insulating housing 
30. The insulating housing 30 is expediently provided with flange elements 
32 for the securing of the deflecting electrode on a schematically 
represented supporting device 19. 
The electrode arrangement of the embodiment according to FIGS. 2 and 3 
consists essentially of a series of approximately prismatic electrode 
bodies 33 constructed of a material having a high electrical resistance 
(order of magnitude 50 M.OMEGA.. cm). The electrode bodies 33 have the 
cross-sectional shape of an approximately isosceles, slender triangle, the 
base of which rests on a height-compensating and spacing piece 34, and the 
vertex of which is approximately flush at the height of the top of the 
housing. The vertex regions 35 of all electrode bodies 33 are disposed, in 
the longitudinal direction of the deflecting electrode 13, on a straight 
line which extends substantially parallel to the longitudinal axis of the 
housing. The electrode bodies 33, which have a width of 1 to 2 cm (seen in 
the longitudinal direction of the electrodes) are separated from one 
another by insulating spacers 36 having a thickness of 1.5 to 3 mm, and, 
according to FIG. 2, are connected in parallel with one another or fed by 
a continuous conductor rod 37. By the subdivision of the entire length of 
the electrode into a relatively large number of discrete lengths 
corresponding to the electrode bodies 33, it is intended on the one hand 
that it should be ensured that a charge field distribution as uniform as 
possible is present along the electrode 13. On the other hand, it is 
intended that the contact current intensity should be kept at a low level 
by the resulting distribution of the overall cross-section of the 
electrode body, in order to prevent the generation of sparks between 
components of mutually opposite polarity. 
The insulating spacers 36 have a thickness of 1.5 to 3 mm and consist of an 
inherently stable material, which is capable of forming an integral body 
in conjunction with a cast resin filling the free spaces 38 in the housing 
30. The insulating spacers 36 are expediently centered with spacing, at 
least in the height-compensating piece 34, in grooves 39, in order to 
achieve a unitary construction of the electrode arrangement 31. 
In the embodiment according to FIGS. 4 and 5, an insulating housing 30 is 
again employed, which is attached to a supporting device 19 by means of 
flange means 32. An electrode arrangement 31' is incorporated in the 
cavity of the housing. This arrangement consists essentially of a central, 
longitudinally extending insulating material supporting wall 40, 
individual resistors 41 which have high resistance and which are disposed 
on both sides thereof and which are fed in parallel, and a series of 
prismatic electrode bodies 43, which are approximately triangular in 
cross-section and which are constructed of a material with preferably a 
high electrical resistance. The latter are fitted in each instance on a 
respective pointed contact element 44, so that they form an electrical 
connection with the outer end of the associated individual resistor 41. 
The individual resistors 41, which have resistance values of 50 to 100 
M.OMEGA., are connected at a lateral spacing from the supporting wall 40 
with the common feeding rail 42 and the contact elements 44 in such a 
manner that they are situated alternately on the two sides of the 
supporting wall 40. Their outer limiting regions are spaced from one 
another to such an extent that these regions at the same time center the 
supporting wall 40 and the triangle vertices of the electrode bodies 43 
within the insulating housing 30 on the central longitudinal plane of the 
electrodes. The triangle vertices of the electrode bodies 43 are, in turn, 
situated approximately at the height of the top of the housing. 
The electrode bodies 43 have a width of approximately 10-20 mm (seen in the 
longitudinal direction of the electrodes) and are separated from one 
another by insulating spacers 45. In order to achieve uniform spacing, the 
latter can be inserted into grooves 46 on the top of the supporting wall 
40. As has already been described with reference to FIG. 2 and FIG. 3, 
this results once again in an optimally uniform charge field distribution 
along the electrode 13. As a result of the individual feeding of the 
electrode bodies 43 via the resistors 41 of high resistance, it is 
furthermore possible also to maintain the contact current intensity at a 
low level and thus to eliminate the danger of the formation of sparks 
between components of mutually opposite polarity. 
The insulating spacers 45 can be constructed of the same material as the 
insulating spacers 36 of FIG. 2, and the free spaces remaining in the 
cavity of the housing between the housing walls and the components of the 
electrode arrangement 31' are filled by a cast resin 47. 
By means of the deflecting electrode 13 divided into discrete longitudinal 
sections in the described manner, it is possible to achieve an optimally 
uniform field distribution along the length of the deflecting electrode 
13. Any differing field strength levels between adjacent electrode 
sections which may result from inhomogeneities in the individual electrode 
bodies 33, 43 and/or unequal resistance values due to tolerances among the 
individual resistors 41 of high resistance are locally limited. 
Differences in levels arising from unequal surface charge at the electrode 
due to dirt, dust and/or moisture are within operationally permissible 
limits. In cases of application in which field strength levels which are 
graduated along the length of the electrode are necessary or expedient, 
provision can readily be made for an electrical separation of the feed 
conductors of individual or groups of electrode bodies 33, 43 from 
adjacent regions. 
The above described deflecting device for viscous coating material flowing 
freely in the form of a sheet may be employed in all cases where the 
coating material is to be brought, without contact, from a first 
(original) direction of flow into a second (deflected) direction of flow. 
As a result of the possibility of operating the deflecting electrodes with 
very low local contact current intensities, the deflecting device 
according to the invention can also be used, without danger, in the 
processing of coating materials with readily flammable solvents.