Ink chamber doctor blade for an inking unit

An arrangement for coating continuous material webs is designed in particular as an inking cell doctor blade for an ink transfer, circular cylindrical screen, such as a screened roller or an engraved cylinder of a printing machine. In the cavity of the inking cell is arranged a profiled body with a pressure nose spaced apart from the outer surface of the screen which forms a flow gap that extends in the axial direction in relation to the screen. The pressure nose further has a relief located behind the screen in its direction of rotation, for a sudden cross-sectional enlargement that causes a sudden pressure drop in the part of the cell cavity located behind the pressure nose. When the circular cylindrical screen is rotated, a high pressure builds up in the wedge-shaped, narrowing flow gap between the pressure nose and the outer surface of the screen. This high pressure presses the liquid printing ink into the cups or recesses located at the circumference of the screen and constantly swirls it therein, so that ink residues and impurities are constantly washed out of the cups and/or recesses and mixed with the supplied printing ink.

FIELD OF THE INVENTION 
The invention concerns a device for coating moving strips of material and 
relates in particular to an ink chamber doctor blade for an inking, 
screened circular cylindrical body such as an engraved roller or gravure 
inking cylinder on a printing press. 
PRIOR ART 
Amongst known single-chamber doctor blades, the ink in the lower part of 
the ink chamber is conveyed either to the centre or to both ends of the 
chamber and then flows into the ink duct in longitudinal direction 
parallel to the engraved roller while being swirled by the rotating 
engraved roller, then being again removed in the upper part of the ink 
chamber. The single-chamber doctor blade has a positive blade and a 
negative blade which scrapes off the surplus paint in the upper part of 
the ink chamber while the engraved roller rotates at a circumferential 
speed of e.g. 100 r.p.m. 
A disadvantage with this is that the very numerous small cups in the 
engraved roller gradually fill up with ink residues and old printing ink 
in the course of time and can then no longer adequately take up new 
printing ink, so that the printing quality deteriorates quite appreciably. 
Engraved rollers must therefore be brushed down and cleaned with highly 
aggressive media at regular, brief intervals, e.g. weekly, which with the 
extremely small screen separation of the cups is highly labour-intensive 
if thorough cleaning is to be achieved. 
In addition, with the known single-chamber doctor blade, a high pressure 
builds up in the ink chamber at higher circumferential speeds of the 
engraved roller through which the upper negative blade may arch outwards 
in the rotatory direction of the roller so that the knife edge of the 
negative blade no longer lies flush along the circumference of the roller, 
but is tilted slightly, resulting in a kind of aquaplaning effect lifting 
the edge of the blade from the circumference of the roller so that the ink 
is no longer completely cleaned from the bridges between the screen cups. 
In addition, it should be noted that liquid ink is composed of solvents and 
solid particles in addition to other components. These solid particles, 
used for pigmentation, are certainly intimately mixed with the solvent, 
yet solid particles may be separated from the solvent by centrifugal force 
which results in a change in color. 
This risk is due especially to uncontrolled swirling of the ink in the 
doctor blade box, which is the greatest at the inlet to the ink chamber on 
the doctor blade box and we assume different dimensions between the inlet 
duct and the outlet duct before again stabilizing only before the outlet 
duct. 
Further, with the known ink chamber doctor blades, whether a cup on the 
engraved roller is filled with fresh ink or not when passing the doctor 
blade box is largely left to chance. Gaps in the printed image are the 
result. This applies analogously also to ink chamber doctor blades with a 
gravure roller on gravure presses and to chamber doctor blades with 
engraved roller for the uniform application of thin layers of adhesive on 
carrier foil or strip material or for applying thin magnetic coatings to 
magnetic tapes e.g. for tape recorder or video cassettes. 
An ink chamber doctor blade of the type first mentioned is known from DE 37 
37 531 A1 which is designed as a forme cleat for a flushing inking 
mechanism on a rotary press. A moulding is fitted in the ink distribution 
chamber on this inking cleat between two doctor blades, around which the 
ink can flow freely and which can pivot or rotate. By this means, by 
creating a uniform ink flow without turbulence, uniform contact is 
possible between the ink and the inking roller at high circumferential 
speeds and an ink flow pressure can be adjusted for better filling of the 
cups on the inking roller. The moulding has an elliptical cross section. 
Tilting the moulding around its axis of rotation therefore produces a 
change of the smallest gap width, the gap being formed by the engraved 
roller and the surface area of the moulding facing the roller. The 
strength of the ink in the gap is at its greatest shortly in front of the 
smallest gap width seen from the direction of the engraved roller. 
According to a formula indicated, a change in the smallest gap width 
therefore results in an immediate [word illegible] in the ink on the 
engraved roller. The moulding is tilted by adjusting devices fitted in 
each case on the outside of the lateral guards of the inking cleat. The 
adjustment can be made by hand or by a servo-motor. 
The moulding may with this known inking cleat also have a wing profile or 
consist of two opposing concave surfaces, whereby, however, the gap width 
is again gradually increased after each narrowing of the gap width between 
the moulding and the surface of the engraved roller and a corresponding 
gradual relaxation is consequently created in the liquid ink pressed into 
the cups on the engraved roller after passing through the engraved roller 
in rotating direction behind the moulding. The ink is compressed only 
slightly in the cups on the engraved roller through the narrowing of the 
gap width and is subsequently not suddenly again relaxed, so that the 
parts of the ink present in the cups are not replaced by new ink. A 
special cleaning and ink exchanging effect is not therefore produced by 
narrowing the gap width alone. 
With another known inking mechanism an ink chamber with a lower inlet and 
an upper outlet between two doctor blades is certainly known with a 
narrowing in the rotating direction of the engraved roller towards the ink 
outlet in order to improve the inking on letter-press rotary presses 
(DE-Zeitschrift ifra zeitungstechnik, September 1989, pages 1-5), but with 
this known inking device, too, the narrowing is so formed that no sudden 
pressure drop occurs in the rotating direction of the engraved roller 
beyond the narrowing. The ink present in the cups on the engraved roller 
is consequently not further swirled after passing through the narrowing in 
the ink chamber before the passage through the negative doctor blade 
arranged behind it in the rotating direction of the engraved roller. 
In a further known coating device for coating moving strips of fabric with 
a coating slip (DE 34 46 757 A1) a guide is certainly fitting in the 
rotating direction of the engraved roller between an inlet for the coating 
slip and a doctor blade element adjoining the coating chamber which, 
however, is at some distance from the engraved roller and consequently can 
neither increase nor reduce the print in the coating mass at the guide as 
it passes along the engraved roller. 
In a further known chamber doctor blade for rotary presses (DE 38 23 340 
C1) at least one additional doctor blade is fitted within the ink chamber, 
whereby the additional doctor blade knife/knives may in the working 
position of the doctor blade chamber device be adjusted against the 
coating roller without necessarily touching the latter. The additional 
doctor blade knife may also be a damping rod blade which will, however, 
lift from the circumference of the coating roller as pressure builds up on 
the blade side. 
A device for coating strips of material running across a back-up impression 
cylinder with adjustable coating thickness and an apportioning chamber is 
known from CH 663 362 A5, in which a return lip is adjustably fitted in 
such a way that a pre-apportioning gap formed by the return lip to a 
pre-apportioning chamber facilitates the creation of a blocking jet 
directed contrary to the circulating direction of the strip of material. 
This is intended to prevent the creation of an air boundary layer in the 
apportioning chamber with the circulating strip of material at very high 
speeds. 
The purpose of the invention is to improve a coating device especially in 
the form of an ink chamber doctor blade as claimed in claim 1 by simple 
technical means in such a way that the ink is more effectively swirled and 
mixed through in the cups at the circumference of the screened or engraved 
cylindrical body on passing through the ink chamber so that the cups are 
filled uniformly with new ink on each passage through the ink chamber and 
depositing of solid particles from the printing ink in the cups is largely 
prevented and the printed image on printed products produced on 
flexographic presses is consequently also quite appreciably improved in 
the long run. 
This problem is solved in a generic coating device according to the 
invention which is hereinafter described in greater detail. 
SUMMARY OF THE INVENTION 
The invention has the advantage that a high pressure is built up by a 
moulding in pressure nozzle form in the wedge-like narrowing flow gap 
between the pressure nozzle and the surface of the moulding on passing 
round the cylindrical body, whereby the liquid ink or the coating medium 
is pressed into the cups on the circumference of the engraved or coating 
roller and is continuously swirled in them. 
By a sudden widening of the cross-section in the rotating direction of the 
cylindrical body behind the pressure nozzle, a sudden pressure drop is 
thereupon produced which results in the printing fluid compressed by the 
pressure nozzle and containing solvents and also mixed with air bubbles 
suddenly relaxing at the cylindrical body and thereby being again washed 
at least partly out of the cups or recesses in the surface of the body and 
being immediately refilled by the superimposed printing fluid, so that 
colour residues and impurities are continuously removed from the cups or 
recesses even in the area behind the pressure nozzle and are continuously 
carried off from the upper part of the ink chamber with the printing 
fluid. 
The lower pressure in the rinsing chamber produced by the rebound and the 
sudden widening of the cross section behind the pressure nozzle has the 
further advantage that a negative doctor blade adjoining the ink chamber 
in the rotating direction of the cylindrical body is not arched outwards 
but instead lies with its knife-type blade-edge at all times smooth and 
flush along the circumference of the cylindrical body without any 
aquaplaning effect or increased wear occurring as in the state of the art. 
This results in an improved stripping by the negative doctor blade of the 
circumference of the roller. Moreover, the edge life of the doctor blade 
is quite appreciably extended. 
The invention therefore has the advantage that the cups or recesses on the 
circumference of the cylindrical roller being washed out in depth by the 
increased pressure in the wedge-shaped narrowing pressure zone between the 
pressure nozzle and the surface of the body and by the subsequent sudden 
pressure drop with cavitation effect, which results in uniform inking of 
the engraved roller/gravure roller and consequently a constant ink 
intensity. 
It is, further, specially advantageous for a uniform colour intensity if 
the distance between the pressure nozzle and the body surface of the 
circular cylindrical body is regulatable by means of an assembly mounting 
adjustable vertically to the rotary direction of the body on the doctor 
blade box, which has the further advantage that the pressure nozzle can 
easily be demounted from and refitted to the doctor blade box for cleaning 
the said box by means of the assembly mounting and cleaning of the doctor 
blade box is thereby in no way obstructed. 
It is further an advantage to the uniform supply and distribution of the 
printing ink over the whole length of the ink chamber doctor blade if the 
forward chamber extending in front of the pressure nozzle in the direction 
of flow of the printing ink is sub-divided by a leading edge parallel to 
the cylindrical body into an injection chamber and a pre-washing chamber, 
linked to each other by a passage stretching across the whole length of 
the forward chamber between the leading edge and the lower side guards of 
the doctor blade box. 
It is furthermore an advantage for the production and assembly of the ink 
chamber doctor blade for the doctor blade box to consist of a bottom with 
upper and lower lateral walls between end walls at each end and for 
horizontal and/or vertical bores to be provided as upper and lower inlets 
and outlets in the lower and upper side walls, from which a bore leads 
vertically or diagonally into the ink chamber in each case. 
It is thereby structurally easily possible for an injection bore to be 
aligned from the inlet vertically opposite and injection duct extending 
along the bottom of the doctor blade box essentially throughout its length 
next to the leading edge, so that a particularly intimate mixing and 
uniform distribution of the printing ink can be achieved in the injection 
duct through the injection duct having a cross-section extending in a 
V-shape towards the ink chamber with a rounded bottom. 
Also especially advantageous for this is the feature wherein the injection 
slot with the injection duct extending in a V-shaped cross-section is 
arranged and inclined against the bottom of the doctor blade box in such a 
way that the ink is conveyed beneath the leading edge limiting the 
injection duct sideways to the pre-rinsing chamber and against the 
circumference of the body. In a further detailed embodiment, the moulding 
includes a separate end wall coupled thereto which projects downwards 
through its length, leaving open an uniformly narrow longitudinal slot 
towards the lower sidewall of the doctor blade box for a uniform laminar 
through-flow of the ink from the injection of the distributing chamber 
into the pre-rinsing chamber which provides a yet greater blending of the 
supply of printing ink to the screened or engraved cylindrical body can be 
achieved. By this means the printing ink does not arrive immediately at 
the circumference of the cylindrical body but must first penetrate through 
a very narrow longitudinal slot approx. 1-2 mm wide beneath the separating 
wall in the lower part of the ink chamber with uniform laminar flow, in 
order from the injection chamber to reach the pre-washing chamber from 
which the printing ink then--as already described above, reaches the upper 
ink chamber through the wedge-shaped longitudinal slot passed the pressure 
nozzle on the moulding, with subsequent cavitation swirling. 
The upper ink chamber can similarly be sub-divided by a vertical upper 
separating wall with a broad upper longitudinal slot into an upper 
subsequent rinsing chamber and a back-flow chamber, from which the 
printing fluid is returned to the ink pump through the outlets. The upper 
ink chamber is kept under continuous under-pressure by suction pipes for 
the ink so that no significant pressure can build up in the upper ink 
chamber. Nonetheless, the cavitation swirling and the continuous 
circulation of the printing fluid in the upper ink chamber ensures that 
the cups or recesses in the cylindrical body are kept filled adequately 
and uniformly. 
The invention therefore has the advantage that the cups or recesses in the 
body surface are rinsed out in depth by the increased pressure in the 
wedge-shaped pressure zone and by the subsequent cavitation effect behind 
the pressure nozzle on the moulding, which results in very uniform inking 
of the screened or engraved body surface and a uniform ink intensity. 
Because of the laminar flow of the printing ink through the narrow lower 
longitudinal slot at the separating wall towards the pre-washing chamber, 
a uniform pre-washing of the cups on the circumference of the roller is 
also achieved. 
Through the low pressure in the upper ink chamber, higher circumferential 
speeds can also be achieved with the engraved roller/gravure roller 
without a negative doctor blade set against the rotating direction of the 
cylindrical body losing its shape and lifting from the circumference of 
the engraved roller through an aquaplaning effect. 
The invention is further aimed at still further improving a coating device 
of this kind so that gas bubbles contained in the ink or in the coating 
medium and in particular air bubbles washed out in the pre-washing chamber 
from the numerous small cups along the engraved roller by the ink newly 
supplied are already separated as the ink enters the wedge-shaped 
narrowing longitudinal slot between the high pressure doctor blade and the 
circumference of the roller and the ink thus cleaned arrives continuously 
on the circumference of the roller. 
This is achieved in accordance with the present invention by fitting 
by-pass openings on the moulding next to the pressure nozzle between the 
pre-washing chamber and the after-rinsing chamber. 
This makes it possible in a particularly advantageous way to have the ink 
circulate in the pre-washing chamber in such a way that gas bubbles 
present in the ink and air bubbles washed from the rotating roller are 
already separated from the ink on passing through the wedge-shaped 
narrowing flow slot between the moulding and the circumference of the 
roller and are removed through the by-pass openings between the 
pre-washing chamber and the after-rinsing chamber. 
In a preferred embodiment of the invention, the moulding includes a 
ventilation slot stretching throughout its length between the pre-washing 
chamber and the after-rinsing chamber. It is advantageous in that case for 
separating the air and gas bubbles from the ink if a swirling gutter with 
a more or less arc-shaped cross-section is located at the inlet side of 
the venting slot. 
The venting slot of the moulding in pressure nozzle and venting nozzle form 
is especially suitable for liquid inks that do not mix well with air. The 
ink rotates in the pre-washing chamber inversely to the direction in which 
the roller rotates. This forces the air from the cups on the circumference 
of the roller which is then necessarily carried to the inlet of the 
venting slot where the air bubbles are separated from the ink which moves 
in wave form and escape through the venting slot into the after-rinsing 
chamber and on to the outlet of the ink chamber. 
The removal of the air and gas bubbles from the ink has the advantage that 
the ink on the engraved roller will not foam. Each cup on the 
circumference of the engraved roller is filled without admixture of air so 
that a better quality printed image is achieved. The drying of the ink in 
the cups on the engraved roller is also opposed, which also helps to 
prevent printing errors. Furthermore, air and gas bubbles must be removed 
from certain printing fluids in order to prevent oxidation of the fluid. 
The separation of gas and air bubbles from the ink can be yet further 
improved by locating a venting edge parallel to the inlet at the venting 
slot at the transition from the swirling gutter to the venting slot which 
separates the air and gas bubbles absorbed from the rotating ink in the 
pre-wash chamber from the ink arriving and diverts it to the venting slot. 
The rising gas and air bubbles can then escape upwards through the venting 
slot that advantageously opens into the after-rinsing chamber in a volted 
area at the top of the moulding. 
To reduce the consumption of ink and to make best possible use of the ink 
circulating it may be advantageous for a by-pass slot to be fitted between 
the bottom of the ink chamber and the back of the moulding to return the 
ink from the after-rinsing chamber to the pre-washing chamber. 
Especially advantageous further developments of the invention appear in the 
following detailed description of the preferred embodiments.

DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The ink chamber doctor blade 1 shown in FIG. 1 for doctor blade printing 
mechanisms with engraved roller/gravure roller on flexographic 
presses/gravure presses consists of a doctor blade box 3 with an ink 
chamber 4 and a positive doctor blade 5 and a negative doctor blade 6, the 
doctor blade or knife sides of which lie against the circumference of an 
inking, screened circular cylindrical body 2 turning in the direction of 
arrow 7. The ink chamber 4 has an inlet 8 at centre bottom and two upper 
outlets 9 for the forced circulation of the liquid ink by an ink pump, not 
shown. 
As is evident from FIGS. 2 to 9 in detail, the ink chamber doctor blades 1 
shown there in cross section in ink chamber 4 display a moulding 11 fitted 
with a pressure nozzle 10 between positive doctor blade 5 and negative 
blade 6 which extends over the whole length of the circular cylindrical 
body 2 and forms an increasingly narrowing wedge-shaped flow gap 12 in the 
direction of rotation 7 of the body 2, whereby the pressure nozzle 10 is 
arranged at such a small distance from the surface of the body 2 that 
liquid pressure builds up in the flow gap 12 and as the cylindrical body 2 
revolves the ink passing the pressure nozzle 10 can reach the upper part 
of ink chamber 4, which serves as an after-rinsing chamber, located behind 
the moulding 11. 
The moulding 11 is formed with a sharp-edged rebound 14 in the direction of 
rotation 7 behind the pressure nozzle 10 for a sudden expansion of the 
cross-section to produce a sudden pressure drop in the liquid emerging 
from the flow gap 12. 
The distance of the pressure nozzle 10 from the circumference of the 
circular cylindrical body 2 can be regulated in the embodiments in FIGS. 
2, 3, 5, 6 and 9 by an assembly mounting 16 on the doctor blade box 3 
adjustable at right angles to the axis of rotation 15 while in the 
simplified embodiment in FIG. 4 the moulding 11 is permanently fitted to 
the bottom 17 of the doctor blade box 3 so that the distance from the 
pressure nozzle 10 to the circumference of the circular cylindrical body 2 
is constant and cannot be changed. 
In the two embodiments in FIGS. 2 and 3, the ink chamber 4 is equipped at 
the back-wall of the doctor blade box 3 above the lower inlet 8 for the 
ink with a horizontal injection duct 18 which is limited by a leading edge 
19, parallel to the circular cylindrical body 2 and pointing diagonally 
downwards. The leading edge 19 divides the forward chamber extending in 
front of the moulding 11 in the direction of flow of the ink into an 
injection chamber 20 and a pre-wash chamber 21, which are linked to each 
other by a passage 23 extending over the entire length of the forward 
chamber between the leading edge 19 and the lower side wall 22 of the 
doctor blade box 3. This passage 23 can be of wider or narrower dimensions 
by forming the leading edge 19 appropriately, as shown in FIGS. 2 and 3. 
As is clear from the sectional drawings of FIGS. 2 to 6 and 9, the doctor 
blade box 3 is composed of a bottom 17 with lower and upper side walls 22, 
24 and end walls at each end. Horizontal and/or vertical bores are fitted 
as lower and upper inlets and outlets 8, 9 in the upper and lower side 
walls 22, 24, of which a vertical and a diagonal bore in each case leads 
to the ink chamber 4. 
From the inlet bore 8, an injection bore or an injection slot 25 is 
directed at right angles to the injection duct 18, which extends along the 
bottom 17 of the doctor blade box 3 mostly over its entire length next to 
the leading edge 19. The injection duct 18 has a cross section widening in 
a V-shape towards the ink chamber 4 with a rounded bottom and the 
injection bore or the injection slot 25 is arranged with the injection 
duct extending with a V-shaped cross section inclined in such a way 
against the bottom 17 of the doctor blade box 3 that the ink mixed in the 
injection duct 18 is conveyed underneath the leading edge 19 limiting the 
injection duct at the side into the pre-wash chamber 21 and against the 
circumference of the engraved roller 2. 
This arrangement of the injection or distribution chamber 20 means that the 
ink is distributed over the whole length of the doctor blade box 3 after 
entering into the lower central inlet 8 and being conveyed through the 
injection bore or the injection slot 25 and the injection duct 18 to both 
sides of the injection chamber 20 and is then mixed more or less helically 
in the injection duct extending above the opening of the injection bore 
25, subsequently entering between the front leading edge 19 and the lower 
side wall 22 of the doctor blade box 3 into the pre-wash chamber 21 
located in front of it, where it is mixed further, in order then to be 
drawn from the circulating circular cylindrical body 2 into the narrow 
flow gap 12 between the circumference of the roller and the longitudinal 
edge of the pressure nozzle 10 parallel with it, whereupon the ink is 
pressed through the pressure build-up into the increasingly narrowing flow 
gap 12 into the cups on the circumference of the engraved roller and is 
uniformly mixed. 
As further shown in FIGS. 2 and 3, the ink after passing through the narrow 
flow gap 12 enters the area of the rebound 14 where a sudden, abrupt 
pressure drop occurs, through which the ink is swirled in such a way by a 
kind of cavitation effect that a wash-out effect is produced in the cups 
or recesses of the circular cylindrical body 2 which leads to a further 
replacement of the ink in the cups which then as the roller turns further 
arrive beneath the negative doctor blade 6 and are relieved by it of 
surplus ink in the bridge areas. 
As is evident in particular from the illustration in FIG. 3, the cavitation 
effect behind the pressure nozzle 10 produces an under-pressure in the 
return chamber 26 or at least so low a pressure that distortion of the 
negative doctor blade 6 is prevented before the ink is removed through the 
two upper outlets 9 and is again available for renewed injection into the 
ink chamber 4 after passing through a filter. 
Further to the two embodiments of FIGS. 2 and 3, as shown in FIGS. 4 to 6, 
a separating wall 27 may project downwards from the mobile 11 for the 
whole of its length and fasten thereto or forming one piece with it, which 
leaves open a uniformly narrow longitudinal slot 28 beneath the side wall 
22 of the doctor blade box 3 for laminar flow of the liquid ink from the 
injection or distribution chamber 20 into the pre-wash chamber 21. 
In addition, with these modified embodiments, an upper separating wall 29 
may also project upwards from the moulding 11 for the whole of its length, 
similarly leaving open a longitudinal slot 30 against the upper side wall 
24 of the doctor blade box 3 for laminar flow of the stripped ink, forming 
an after-rinsing chamber 31 behind the return chamber 26. 
As shown in FIG. 4, where the lower and upper separating walls 27, 29 are 
subsequently fastened to the moulding 11, the upper separating wall 29 may 
also leave open a return slot 32 for the circulation and additional 
swirling of the ink stripped from the body 2 between return chamber 26 and 
after-rinsing chamber 31. 
Instead of the embodiment shown in FIG. 4, the moulding 11 may, however, 
form one piece with the lower separating wall 27 and also with the upper 
separating wall 29, as FIGS. 5 and 6 show, whereby the projecting walls 
27, 29 projecting downwards and upwards from the moulding 11 may display 
angular or rounded longitudinal edges in accordance with FIGS. 5 or 6. 
In all the embodiments shown, the sharp-edged rebound 14 is rounded more or 
less in an arc behind the pressure nozzle 10 and when joining the rounding 
33 is transformed into a wall section 34 rising more or less tangentially 
and displaced in parallel to the circumference of the circular cylindrical 
body 2. Flow deflectors 35, 36 for the ink are arranged in the form of 
enhanced longitudinal edges next to the positive doctor blade 5 and also 
next to the negative doctor blade 6, which also further help to reduce the 
liquid pressure against the inner edge of the doctor blade knife. 
In the further developed embodiment of FIG. 9, by-pass openings exist next 
to the pressure nozzle between the pre-wash chamber 21 and the 
after-rinsing chamber 31 to improve cleaning of gas and air bubbles from 
the ink and to improve circulation of the ink in the ink chamber doctor 
blade 1 at the moulding 11. 
The moulding 11 displays a venting slot 40 expanding for the whole of its 
length between the pre-wash chamber 21 and the after-rinsing chamber 31 
and is equipped at the inlet side of the venting slot 40 with a swirling 
gutter shaped more or less like an arc in cross-section. 
The transition of the swirling gutter 41 with the venting slot 40 a venting 
edge 42 extends in parallel with the inlet of the venting slot, which 
separates the air and gas bubbles absorbed in the pre-wash chamber 21 from 
rotating ink and guides them to the venting slot 40. The venting slot 40 
opens out into the after-rinsing chamber 31 in a vaulted area 43 at the 
upper side of the moulding 11. 
A bypass slot 44 is located between the bottom 17 of the ink chamber 4 and 
the back of the moulding 11 to return ink from the after-rinsing chamber 
31 to the pre-wash chamber 21. The width of this bypass slot may for 
example be changed by the assembly mounting 16 for the moulding 11 and 
retained by spacer rings 45 on the bolt for the assembly mounting 16. 
The moulding 11 further has a separating wall 27 projecting into the 
pre-wash chamber 21, the lower longitudinal edge 46 of which runs at a 
small lateral distance in parallel with the inside of the lower side wall 
22 of ink chamber 4, and leaves an opening narrowing and again widening in 
the nature of a venturi valve in the flow direction of the ink 
(longitudinal slot 28) to the pre-wash chamber 21. 
Especially good flow is achieved if the lower separating wall 27 of the 
profile body 11 adjoining the bypass slot 44 slopes away in the direction 
of flow of the ink towards the pre-wash chamber 21 and is rounded as 
against the inside of the lower side wall 22 of the ink chamber 4. 
The flow in the pre-wash chamber 21 may be further improved if the lower 
separating wall 27 of the moulding 11 is so inclined as against the 
positive doctor blade 5 that the pre-wash chamber 21 displays a gradually 
widening cross section in the direction of flow of the ink. 
In all the embodiments shown, the doctor blades adjoining the ink chamber 4 
in the circumferential direction of the circular cylindrical body 2 may 
take the form of negative doctor blades instead of positive doctor blades 
5 or of positive doctor blades instead of the negative doctor blades 6, 
entirely according to the various coating requirements made. 
As with doctor blade presses, chamber doctor blades of this kind can also 
be advantageously used for applying thin layers of adhesive to strip 
material and for applying magnetic coatings to tape material for recording 
tapes and video cassettes and for other comparable coating purposes. 
List of reference symbols 
1. Ink chamber doctor blade 
2. Circular cylindrical body 
3. Doctor blade box 
4. Ink chamber 
5. Positive doctor blade 
6. Negative doctor blade 
7. Direction of rotation 
8. Inlet 
9. Outlet 
10. Pressure nozzle 
11. Moulding 
12. Flow gap 
14. Rebound 
15. Axis of rotation 
16. Assembly mounting 
17. Bottle 
18. Injection duct 
19. Leading edge 
20. Injection chamber 
21. Pre-washing chamber 
22. Lower side wall 
23. Passage 
24. Upper side wall 
25. Injection bore/Injection slot 
26. Return chamber 
27. Lower separating wall 
28. Longitudinal slot 
29. Upper separating wall 
30. Longitudinal slot 
31. After-rinsing chamber 
32. Return slot 
33. Rounding 
34. Wall section 
35. Flow deflection (Positive doctor blade) 
36. Flow deflection (Negative doctor blade) 
40. Venting slot 
41. Swirling gutter 
42. Venting edge 
43. Vaulted area 
44. Bypass slot 
45. Spacer ring 
46. Longitudinal edge